Search

A new relaxion mechanism is proposed where a small electroweak scale is preferably selected earlier than the larger one due to a potential instability, which is different from previously proposed stopping mechanisms by either Hubble friction from an increasing periodic barrier or thermal friction from gauge boson production. The sub-Planckian field excursion of an axion can be achieved without violating the bound on the e-folding number from a quantum gravity perspective; our relaxion can be identified as a QCD axion, preserving the Peccei-Quinn solution to the strong CP problem as well as making up all the cold dark matter in our current Universe. [ABSTRACT FROM AUTHOR]

White dwarfs (WD) capture dark matter (DM) as they orbit within their host halos. These captured particles may subsequently annihilate, heating the stellar core and preventing the WD from cooling. The potential wells of WDs are considerably deeper and core temperatures significantly cooler than those of main sequence stars. Consequently, DM evaporation is less important in WDs and DM with masses Mχ≳100 keV, and annihilation cross sections orders of magnitude below the canonical thermal cross section (σav≳10−46 cm³/s) can significantly alter WD cooling in particular astrophysical environments. We consider WDs in globular clusters (GCs) and dwarf galaxies. If the parameters of the DM particle are known, then the temperature of the coolest WD in a GC can be used to constrain the DM density of the cluster's halo (potentially even ruling out the presence of a halo if the inferred density is of order the ambient Galactic density). Recently, several direct detection experiments have seen signals whose origins might be due to low mass DM. In this paper, we show that if these claims from CRESST, DAMA, CDMS-Si, and CoGeNT could be interpreted as DM, then observations of NGC 6397 limit the fraction of DM in that cluster to be fDM≲10−3. This would be an improvement over existing constraints of 3 orders of magnitude and would clearly rule out a significant DM halo for this cluster. More generally, we show how such observations constrain combinations of DM and GC properties. Building on previous work, we also show how observations of WDs in dwarf galaxies, such as Segue I, can provide novel constraints on low-mass DM or DM with very low contemporary annihilation cross sections as may be realized in models in which s-wave annihilation is suppressed and p-wave annihilation dominates. This paper provides further motivation for high-quality observations of stellar populations as a probe of dark matter. [ABSTRACT FROM AUTHOR]

In performing cosmological N-body simulations, it is widely appreciated that the growth of structure on the largest scales within a simulation box will be inhibited by the finite size of the simulation volume. Following ideas set forth by Seto Astrophys. J. 523, 24 (1999), this paper shows that standard (also known as one-loop) cosmological perturbation theory (SPT) [E. T. Vishniac, Mon. Not. R. Astron. Soc. 203, 345 (1983)] can be used to predict, in an approximate way, the deleterious effect of the box scale on the power spectrum of density fluctuations in simulation volumes. Alternatively, this approach can be used to quickly estimate post facto the effect of the box scale on power spectrum results from existing simulations. In this way SPT can help determine whether larger box sizes or other more-sophisticated methods are needed to achieve a particular level of precision for a given application (e.g. simulations to measure the nonlinear evolution of baryon acoustic oscillations). I focus on SPT in this paper and show that its predictions differ only by about a factor of 2 or less from the measured suppression inferred from both power law and ACDM

The standard cosmological model assumes that more than 85% of matter is in the form of collisionless and pressureless dark matter. Unstable decaying dark matter has been proposed in the literature as an extension to the standard cold dark matter model. In this paper, we investigate a scenario when dark matter decays, and the resultant particle moves with respect to the dark matter. A covariant hydrodynamical model is developed in which the decay is modeled by the transfer of energy-momentum between two dark dust fluid components. We parametrize the model in terms of the decay rate Γ and injection velocity vi of the resultant dark matter particles. We apply the framework to study the evolution of cosmic voids which are environments with low content of baryonic matter. Thus, unlike baryon-rich environments, voids provide an opportunity to measure dark matter signals that are less contaminated by complex baryonic processes. We find that the growth of S-type voids is modified by the dark matter decay, leading to imprints at the present day. This paper serves as a proof of concept that cosmic voids can be used to study dark mater physics. We argue that future cosmological observations of voids should focus on signs of reported features to either confirm or rule out the decaying dark matter scenario. Lack of presence of reported features could put constraints of the decay of dark matter in terms of Γ>H-10 and vi<10 km/s. [ABSTRACT FROM AUTHOR]

Solar neutrinos upscattering inside the Earth can source unstable particles that subsequently decay inside large volume detectors (e.g., neutrino experiments). Contrary to naive expectations, when the decay length is much shorter than the radius of the Earth (rather than the length of the detector), the event rate is independent of the decay length. In this paper, we study a neutrino-dipole portal (transition dipole operator) and show that existing data from Borexino and Super-Kamiokande probes previously untouched parameter space in the 0.5-20 MeV regime, complementing recent cosmological and supernova bounds. We discuss similarities and differences with luminous dark matter and comment on future prospects for analogous signals stemming from atmospheric neutrinos. A companion paper explores an analogous mass-mixing portal. [ABSTRACT FROM AUTHOR]

The present paper is the first in a series that addresses the calculation of the full one-loop corrections of dark matter (DM) annihilation cross sections in the low mass region of the inert doublet model (IDM). This series is a sequel to our recent publication concerning these corrections in the high mass region. We first review the renormalization of the model both in a fully on shell (OS) scheme as well as in a mixed scheme that combines on shell (for the masses) and a MS approach when the partial invisible width is closed and does not allow the use of a full OS scheme. The scale dependence introduced by the mixed scheme is shown to be tracked through an analysis of a parametrization of the tree-level cross section and the β constant of a specific coupling; this analysis could be followed in theories. We discuss how to minimize the scale dependence. The theoretical uncertainty brought by the scale dependence leads us to introduce a new criterion on the perturbativity of the IDM. This criterion further delimits the allowed parameter space, which we investigate carefully by including a host of constraints, both theoretical and experimental, including in particular, new data from the LHC. We come up with a set of benchmark points that cover three different mechanisms for a viable relic density of DM: (i) a dominance of coannihilation into a fermion pair, (ii) annihilation into two vector bosons of which one is off shell that requires the calculation of a 2 → 3 process, (iii) annihilation that proceeds through the very narrow standard model Higgs resonance. Since the 2 → 3 vector boson channel features in all three channels and is essentially a buildup on the simpler annihilation to OS vector bosons, we study the latter in detail in the present paper. We confirm again that the corrected cross sections involve a parameter that can be considered as rescattering in the dark sector, which a tree-level computation is not sensitive to. The setup of the renormalization detailed in the present paper will be the backbone of the accompanying papers where each mechanism requires, calculationally, a specific treatment. One-loop corrections to 2 → 3 processes for DM annihilation are technically challenging and have not been attempted before. We dedicate one of the accompanying papers to such a computation. The one-loop correction in the presence of a resonance will be presented separately since we need to supplement our general schemes with a complex scheme. For the coannihilation into fermions, our study will show that the annihilation cross sections can be excellently parametrized through simple effective couplings. [ABSTRACT FROM AUTHOR]

In all inflationary scenarios of primordial black hole (PBH) formation, amplified scalar perturbations inevitably accompany an induced stochastic gravitational wave background (ISGWB) at smaller scales. In this paper, we study the ISGWB originating from the inflationary model, introduced in our previous paper [N. Bhaumik and R. K. Jain, Primordial black holes dark matter from inflection point models of inflation and the effects of reheating, J. Cosmol. Astropart. Phys. 01 (2020) 037] wherein PBHs can be produced with a nearly monochromatic mass fraction in the asteroid mass window accounting for the total dark matter in the universe. We numerically calculate the ISGWB in our scenario for frequencies ranging from nano-Hz to kHz that covers the observational scales corresponding to future space-based gravitational wave (GW) observatories such as IPTA, LISA, DECIGO, and Einstein Telescope. Interestingly, we find that ultralight PBHs (MPBH∼10-20 M⊙), which shall completely evaporate by today with an exceedingly small contribution to dark matter, would still generate an ISGWB that may be detected by a future design of the ground-based Advanced LIGO detector. Using a model-independent approach, we obtain a stringent lower mass limit for ultralight PBHs which would be valid for a large class of ultra slow roll inflationary models. Further, we extend our formalism to study the imprints of a reheating epoch on both the ISGWB and the derived lower mass bound. We find that any noninstantaneous reheating leads to an even stronger lower bound on the PBH mass and an epoch of a prolonged matter-dominated reheating shifts the ISGWB spectrum to smaller frequencies. In particular, we show that an epoch of an early matter-dominated phase leads to a secondary amplification of the ISGWB at a much smaller scale corresponding to the smallest comoving scale leaving the horizon during inflation or the end of the inflation scale. Finally, we discuss the prospects of the ISGWB detection by the proposed and upcoming GW observatories. [ABSTRACT FROM AUTHOR]

passes smoothly it, without any catastrophic effects. Then the question is if the effects of a type IV singularity can be detected in the process of cosmic evolution. In this paper we address this question in the context of F{R) gravity. As we demonstrate, the effects of a type IV singularity appear in the Hubble flow parameters, which determine the dynamical evolution of the cosmological system. So we study various inflation models incorporating a type IV singularity, with the singularity occurring at the end of inflation. Particularly we study a toy model and a singular version of the R² gravity Hubble rate. As we evince, some of the Hubble flow parameters become singular at the singularity, an effect which indicates that at that point a dynamical instability occurs. This dynamical instability eventually indicates the graceful exit from inflation. We demonstrate that the toy model has an unstable de Sitter point at the singularity, so indeed graceful exit could be triggered. In the case of the singular inflation model, graceful exit proceeds in the standard way. In addition, we investigate how the form of the F(R) gravity affects the singularity structure of the Hubble flow parameters. In the case of the singular inflation model, we found various scenarios for singular evolution, most of which are compatible with observations, and only one leads to severe instabilities. In addition, in one of these scenarios, the presence of the type IV singularity slightly modifies the spectral index of primordial curvature perturbations. We also compare the ordinary Starobinsky with the singular inflation model, and we point out the qualitative and quantitative differences. Finally, we study the late-time dynamics of the toy model and of the singular inflation model and we demonstrate that the unification of early and late-time acceleration can be achieved. We also show that it is possible to achieve late-time acceleration similar to the A-cold dark matter model. [ABSTRACT FROM AUTHOR]

A nonminimal coupling between the dark matter and dark energy components may offer a way of solving the so-called coincidence problem. In this paper we propose a low-z test for such hypothesis using measurements of the gas mass fraction f gas in relaxed and massive galaxy clusters. The test applies to any model whose dilution of dark matter is modified with respect to the standard a-3 scaling, as usual in interacting models, where a is the cosmological scale factor. We apply the test to current fgas data and perform Monte Carlo simulations to forecast the necessary improvements in number and accuracy of upcoming observations to detect a possible interaction in the cosmological dark sector. Our results show that improvements in the present relative error Ψgas/fgas are more effective to achieve this goal than an increase in the size of the fgas sample. [ABSTRACT FROM AUTHOR]

Cosmological constraints are usually derived under the assumption of a six-parameter ACDM theoretical framework or simple one-parameter extensions. In this paper we present, for the first time, cosmological constraints in a significantly extended scenario, varying up to 12 cosmological parameters simultaneously, including the sum of neutrino masses, the neutrino effective number, the dark energy equation of state, the gravitational wave background and the running of the spectral index of primordial perturbations. Using the latest Planck 2015 data release (with polarization), we found no significant indication for extensions to the standard ACDM scenario, with the notable exception of the angular power spectrum lensing amplitude, Alens' which is larger than the expected value at more than 2 standard deviations, even when combining the Planck data with BAO and supemovae type la external data sets. In our extended cosmological framework, we find that a combined Planck + BAO analysis constrains the value of the rms density fluctuation parameter to σ

Using 137,562 quasars in the redshift range 2.1 ≤ z ≤ 3.5 from the data release 11 (DR11) of the baryon oscillation spectroscopic survey (BOSS) of Sloan Digital Sky Survey (SDSS)-III, the BOSS-SDSS collaboration estimated the expansion rate H[z = 2.34) = 222 ± 7 km/s/Mpc of the Universe, and reported that this value is in tension with the predictions of flat ΛCDM model at around a 2.5a level. In this paper, we briefly describe some attempts made in the literature to relieve the tension, and show that the tension can naturally be alleviated in a nonflat ΛCDM model with positive curvature. We also perform the observational consistency check by considering the constraints on the nonflat ΛCDM model from Planck, WP and B AO data. We find that the nonflat ΛCDM model constrained with Planck + WP data fits better to the line of sight measurement H(z = 2.34) = 222 ± 7 km/s/Mpc, but only at the expense of still having a poor fit to the BAO transverse measurements. [ABSTRACT FROM AUTHOR]

This paper treats nonrelativistic matter and a scalar field ϕ with a monotonically decreasing potential minimally coupled to gravity in flat Friedmann-Lemaître-Robertson-Walker cosmology. The field equations are reformulated as a three-dimensional dynamical system on an extended compact state space, complemented with cosmographic diagrams. A dynamical systems analysis provides global dynamical results describing possible asymptotic behavior. It is shown that one should impose global and asymptotic bounds on λ = -V-1 dV/dϕ to obtain viable cosmological models that continuously deform ACDM cosmology. In particular we introduce a regularized inverse power-law potential as a simple specific example. [ABSTRACT FROM AUTHOR]

This paper presents a search for Higgs bosons decaying to four leptons, either electrons or muons, via one or two light exotic gauge bosons Zd, H → ZZd → 4l or H → ZdZd 4l. The search was performed using pp collision data corresponding to an integrated luminosity of about 20 fb-1 at the center-of-mass energy of √s = 8 TeV recorded with the ATLAS detector at the Large Hadron Collider. The observed data are well described by the Standard Model prediction. Upper bounds on the branching ratio of H → ZZd → 4l and on the kinetic mixing parameter between the Zd and the Standard Model hypercharge gauge boson are set in the range (1-9) × 10-5 and (4-17) × 10-5 respectively, at 95% confidence level assuming the Standard Model branching ratio of H → ZZ* → 4l, for Zd masses between 15 and 55 GeV. Upper bounds on the effective mass mixing parameter between the Z and the Zd are also set using the branching ratio limits in the H → ZZd → 4l search, and are in the range (1.5-8.7) × 10-4 for 15 < mZd < 35 GeV. Upper bounds on the branching ratio of H → ZdZd → 4l and on the Higgs portal coupling parameter, controlling the strength of the coupling of the Higgs boson to dark vector bosons are set in the range (2-3) × 10-5 and (1-10) × 10-5 respectively, at 95% confidence level assuming the Standard Model Higgs boson production cross sections, for Zd masses between 15 and 60 GeV. [ABSTRACT FROM AUTHOR]

We present a new model of stealth dark matter: a composite baryonic scalar of an SU(ND) strongly coupled theory with even ND ≥ 4. All mass scales are technically natural, and dark matter stability is automatic without imposing an additional discrete or global symmetry. Constituent fermions transform in vectorlike representations of the electroweak group that permit both electroweak-breaking and electroweak- preserving mass terms. This gives a tunable coupling of stealth dark matter to the Higgs boson independent of the dark matter mass itself. We specialize to SU(4), and investigate the constraints on the model from dark meson decay, electroweak precision measurements, basic collider limits, and spinindependent direct detection scattering through Higgs exchange. We exploit our earlier lattice simulations that determined the composite spectrum as well as the effective Higgs coupling of stealth dark matter in order to place bounds from direct detection, excluding constituent fermions with dominantly electroweakbreaking masses. A lower bound on the dark baryon mass mB ≿ 300 GeV is obtained from the indirect requirement that the lightest dark meson not be observable at LEP II. We briefly survey some intriguing properties of stealth dark matter that are worthy of future study, including collider studies of dark meson production and decay; indirect detection signals from annihilation; relic abundance estimates for both symmetric and asymmetric mechanisms; and direct detection through electromagnetic polarizability, a detailed study of which will appear in a companion paper. [ABSTRACT FROM AUTHOR]

This paper examines the properties of "lattice universes" wherein point masses are arranged in a regular lattice on spacelike hypersurfaces; open, flat, and closed universes are considered. The universes are modeled using the Lindquist-Wheeler (LW) approximation scheme, which approximates the space-time in each lattice cell by Schwarzschild geometry. Extending Lindquist and Wheeler's work, we derive cosmological scale factors describing the evolution of all three types of universes, and we use these scale factors to show that the universes' dynamics strongly resemble those of Friedmann-Lemaitre-Robertson- Walker (FLRW) universes. In particular, we use the scale factors to make more salient the resemblance between Clifton and Ferreira's Friedmann-like equations for the LW models and the actual Friedmann equations of FLRW space-times. Cosmological redshifts for such universes are then determined numerically, using a modification of Clifton and Ferreira's approach; the redshifts are found to closely resemble their FLRW counterparts, though with certain differences attributable to the "lumpiness" in the underlying matter content. Most notably, the LW redshifts can differ from their FLRW counterparts by as much as 30%, even though they increase linearly with FLRW redshifts, and they exhibit a nonzero integrated Sachs-Wolfe effect, something which would not be possible in matter-dominated FLRW universes without a cosmological constant. [ABSTRACT FROM AUTHOR]

The transit of primordial black holes through a white dwarf causes localized heating around the trajectory of the black hole through dynamical friction. For sufficiently massive black holes, this heat can initiate runaway thermonuclear fusion causing the white dwarf to explode as a supernova. The shape of the observed distribution of white dwarfs with masses up to 1.25M☉ rules out primordial black holes with masses ∼1019-1020 gm as a dominant constituent of the local dark matter density. Black holes with masses as large as 1024 gm will be excluded if recent observations by the NuStar Collaboration of a population of white dwarfs near the galactic center are confirmed. Black holes in the mass range 1020-1022 gm are also constrained by the observed supernova rate, though these bounds are subject to astrophysical uncertainties. These bounds can be further strengthened through measurements of white dwarf binaries in gravitational wave observatories. The mechanism proposed in this paper can constrain a variety of other dark matter scenarios such as Q balls, annihilation/collision of large composite states of dark matter and models of dark matter where the accretion of dark matter leads to the formation of compact cores within the star. White dwarfs, with their astronomical lifetimes and sizes, can thus act as large spacetime volume detectors enabling a unique probe of the properties of dark matter, especially of dark matter candidates that have low number density. This mechanism also raises the intriguing possibility that a class of supernova may be triggered through rare events induced by dark matter rather than the conventional mechanism of accreting white dwarfs that explode upon reaching the Chandrasekhar mass. [ABSTRACT FROM AUTHOR]

We propose a new class of dark matter models with unusual phenomenology. What is ordinary about our models is that dark matter particles are weakly interacting massive particles; they are weakly coupled to the standard model and have weak scale masses. What is unusual is that they come in multiplets of a new dark non-Abelian gauge group with milliweak coupling. The massless dark gluons of this dark gauge group contribute to the energy density of the Universe as a form of weakly self-interacting dark radiation. In this paper we explore the consequences of having (i) dark matter in multiplets, (ii) self-interacting dark radiation, and (iii) dark matter which is weakly coupled to dark radiation. We find that (i) dark matter cross sections are modified by multiplicity factors which have significant consequences for collider searches and indirect detection, and (ii) dark gluons have thermal abundances which affect the cosmic microwave background (CMB) as dark radiation. Unlike additional massless neutrino species the dark gluons are interacting and have vanishing viscosity and (iii) the coupling of dark radiation to dark matter represents a new mechanism for damping the large scale structure power spectrum. A combination of additional radiation and slightly damped structure is interesting because it can remove tensions between global ACDM fits from the CMB and direct measurements of the Hubble expansion rate (H0) and large scale structure (σ8). [ABSTRACT FROM AUTHOR]

In this paper we present a new scenario where massive primordial black holes (PBHs) are produced from the collapse of large curvature perturbations generated during a mild-waterfall phase of hybrid inflation. We determine the values of the inflaton potential parameters leading to a PBH mass spectrum peaking on planetary like masses at matter-radiation equality and producing abundances comparable to those of dark matter today, while the matter power spectrum on scales probed by cosmic microwave background (CMB) anisotropics agrees with Planck data. These PBHs could have acquired large stellar masses today, via merging, and the model passes both the constraints from CMB distortions and microlensing. This scenario is supported by Chandra observations of numerous BH candidates in the central region of Andromeda. Moreover, the tail of the PBH mass distribution could be responsible for the seeds of supermassive black holes at the center of galaxies, as well as for ultraluminous x-ray sources. We find that our effective hybrid potential can originate e.g. from D-term inflation with a Fayet-Iliopoulos term of the order of the Planck scale but sub-Planckian values of the inflaton field. Finally, we discuss the implications of quantum diffusion at the instability point of the potential, able to generate a Swiss-cheese-like structure of the Universe, eventually leading to apparent accelerated cosmic expansion. [ABSTRACT FROM AUTHOR]

The gamma-ray excess observed by the Fermi-LAT in the Galactic Center can be interpreted by the dark matter annihilation to bb via a light pseudoscalar in the next-to-minimal supersymmetric standard model (NMSSM). It is interesting to note that the corresponding singlet scalar is useful to achieve a strongly firstorder phase transition required by the electroweak baryogenesis. In this paper, we investigate the possibility that the NMSSM model can simultaneously accommodate these two issues. The phase transition strength can be characterized by the vacua energy gap at zero temperature and be sufficiently enhanced by the treelevel effect in the NMSSM. We find that the annihilation of singlino/Higgsino dark matter (DM) particles occurring close to the light pseudoscalar resonance is favored by the Galactic Center excess and the observed DM relic density, and some resulting regions in the parameter space with a small κ/λ and a negative Aκ can simultaneously account for a successful strongly first-order electroweak phase transition. [ABSTRACT FROM AUTHOR]

It may well happen that the two main components of the dark sector of the Universe, dark matter and dark energy, do not evolve separately but interact nongravitationally with one another. However, given our current lack of knowledge of the microscopic nature of these two components, there is no clear theoretical path to determine their interaction. Yet, over the years, phenomenological interaction terms have been proposed on mathematical simplicity and heuristic arguments. In this paper, based on the likely evolution of the ratio between the energy densities of these dark components, we lay down reasonable criteria to obtain phenomenological, useful, expressions of the said term independent of any gravity theory. We illustrate this with different proposals which seem compatible with the known evolution of the Universe at the background level. Likewise, we show that two possible degeneracies with noninteracting models are only apparent as they can be readily broken at the background level. Further, we analyze some interaction terms that appear in the literature. [ABSTRACT FROM AUTHOR]

In canonical quantum cosmology, the wave function of the Universe lacks explicit time dependence. However, time evolution may be present implicitly through the semiclassical superspace variables, which themselves depend on time in classical dynamics. In this paper, we apply this approach to an oscillating universe model recently introduced by Graham et al. [A simple harmonic universe, J. High Energy Phys. 02 (2014) 029.] By extending the model to include a massless, minimally coupled scalar field ɸ which has little effect on the dynamics but can play the role of a "clock," we determine the decay rate of the oscillating universe. [ABSTRACT FROM AUTHOR]

We consider a light supersymmetric top-quark (top-squark) scenario, where a top squark and a neutralino are the lightest supersymmetric particles and the top-squark mass is close to the sum of the neutralino mass and the top-quark mass. In this scenario, the top quark and the neutralino coming from the decay of a top squark have almost equal velocity vectors, and hence the missing transverse momentum in top-squark pair production events at colliders is suppressed, which makes the top-squark search challenging, as in the degenerate scenario where the top-squark mass and the neutralino mass are similar. In this paper, we propose a novel analysis technique aimed at discovering the top-squark pair production signal in such an "equal-velocity" scenario. The key is to look for events where the missing transverse momentum vector is proportional to the transverse momentum vector of the top-quark pair with specific values for the proportionality coefficient, as this coefficient is equal to the ratio of the neutralino mass over the top-quark mass in the equal-velocity limit. We examine the possibility that the top-squark signal can be identified at the √s = 14 TeV LHC using our analysis method. [ABSTRACT FROM AUTHOR]

A number of groups have employed radio observations of the Galactic center to derive stringent constraints on the annihilation cross section of weakly interacting dark matter. In this paper, we show that electron energy losses in this region are likely to be dominated by inverse Compton scattering on the interstellar radiation field, rather than by synchrotron, considerably relaxing the constraints on the dark matter annihilation cross section compared to previous works. Strong convective winds, which are well motivated by recent observations, may also significantly weaken synchrotron constraints. After taking these factors into account, we find that radio constraints on annihilating dark matter are orders of magnitude less stringent than previously reported, and are generally weaker than those derived from current gamma-ray observations. [ABSTRACT FROM AUTHOR]

We show that the observed rotation curves of spiral galaxies constrain the sound speed of the dark matter to be cs < 10-4c, where c is the speed of light in vacuum. Using the modified Chaplygin gas as a representative example of a class of unified dark energy models incorporating an effective dark matter component with a nonzero sound speed, we determine the most stringent constraint to date on the value of the constant contribution to the equation of state parameter in this class of models. Finally, we explain the reason why previous constraints using the cosmic microwave background and baryonic acoustic oscillations were not as competitive as the one presented in this paper and discuss the limitations of the recently proposed extended Chaplygin gas. [ABSTRACT FROM AUTHOR]

Models in which dark matter particles can scatter into a slightly heavier state which promptly decays to the lighter state and a photon (known as eXciting Dark Matter, or XDM) have been shown to be capable of generating the 3.55 keV line observed from galaxy clusters, while suppressing the flux of such a line from smaller halos, including dwarf galaxies. In most of the XDM models discussed in the literature, this up-scattering is mediated by a new light particle, and dark matter annihilations proceed into pairs of this same light state. In these models, the dark matter and the mediator effectively reside within a hidden sector, without sizable couplings to the Standard Model. In this paper, we explore a model of XDM that does not include a hidden sector. Instead, the dark matter both up-scatters and annihilates through the near resonant exchange of an O(10²) GeV pseudoscalar with large Yukawa couplings to the dark matter and smaller, but non-neglibile, couplings to Standard Model fermions. The dark matter and the mediator are each mixtures of Standard Model singlets and SU(2)W doublets. We identify parameter space in which this model can simultaneously generate the 3.55 keV line and the gamma-ray excess observed from the Galactic center, without conflicting with constraints from colliders, direct detection experiments, or observations of dwarf galaxies. [ABSTRACT FROM AUTHOR]

We consider the possibility that dark matter halos are described by the Fermi-Dirac distribution at finite temperature. This is the case if dark matter is a self-gravitating quantum gas made of massive neutrinos at statistical equilibrium. This is also the case if dark matter can be treated as a self-gravitating collisionless gas experiencing Lynden-Bell's type of violent relaxation. In order to avoid the infinite mass problem and carry out a rigorous stability analysis, we consider the fermionic King model. In this paper, we study the nondegenerate limit leading to the classical King model. This model was initially introduced to describe globular clusters. We propose to apply it also to large dark matter halos where quantum effects are negligible. We determine the caloric curve and study the thermodynamical stability of the different configurations. Equilibrium states exist only above a critical energy Ec in the microcanonical ensemble and only above a critical temperature Tc in the canonical ensemble. For E

The Alpha Magnetic Spectrometer (AMS-02) has just published the unprecedentedly precise measurement of the cosmic electron and positron spectra. In this paper, we try to give a quantitative study on the AMS-02 results by a global fitting to the electron and positron spectra, together with the updated positron fraction data. The Markov chain Monte Carlo algorithm is adopted to do the fitting. The primary electron spectrum and the parameters for pulsars or dark matter that contribute extra positrons are determined simultaneously. We find that there is a hardening of the primary electron spectrum at ~60 GeV. With such a new feature at the background spectrum, both the pulsars and dark matter can explain the AMS-02 results very well. The dark matter scenario shows a drop at the positron fraction at ~300 GeV but suffers very strong constraints from Fermi γ-ray observations. The fitting results also suggest that the propagation model with convection may be more favored by the lepton data than the reacceleration model. [ABSTRACT FROM AUTHOR]

Among laboratory probes of dark matter, fixed-target neutrino experiments are particularly well suited to search for light weakly coupled dark sectors. In this paper, we show that the DAE5ALUS source setup--an 800 MeV proton beam impinging on a target of graphite and copper--can improve the present LSND bound on dark photon models by an order of magnitude over much of the accessible parameter space for light dark matter when paired with a suitable neutrino detector such as LENA. Interestingly, both DAE5ALUS and LSND are sensitive to dark matter produced from off-shell dark photons. We show for the first time that LSND can be competitive with searches for visible dark photon decays and that fixed-target experiments have sensitivity to a much larger range of heavy dark photon masses than previously thought. We review the mechanism for dark matter production and detection through a dark photon mediator, discuss the beam-off and beam-on backgrounds, and present the sensitivity in dark photon kinetic mixing for both the DAE5ALUS/LENA setup and LSND in both the on- and off-shell regimes. [ABSTRACT FROM AUTHOR]

Cosmology based on large scale peculiar velocity prefers volume weighted velocity statistics. However, measuring the volume weighted velocity statistics from inhomogeneously distributed galaxies (simulation particles/halos) suffers from an inevitable and significant sampling artifact. We study this sampling artifact in the velocity power spectrum measured by the nearest particle velocity assignment method by Zheng et al., [Phys. Rev. D 88, 103510 (2013).]. We derive the analytical expression of leading and higher order terms. We find that the sampling artifact suppresses the z = 0 E-mode velocity power spectrum by ~10% at k = 0.1 h/Mpc, for samples with number density 10-3 (Mpc/h)-3. This suppression becomes larger for larger k and for sparser samples. We argue that this source of systematic errors in peculiar velocity cosmology, albeit severe, can be self-calibrated in the framework of our theoretical modelling. We also work out the sampling artifact in the density-velocity cross power spectrum measurement. A more robust evaluation of related statistics through simulations will be presented in a companion paper by Zheng et al., [Sampling artifact in volume weighted velocity measurement. II. Detection in simulations and comparison with theoretical modelling, arXiv: 1409.6809.]. We also argue that similar sampling artifact exists in other velocity assignment methods and hence must be carefully corrected to avoid systematic bias in peculiar velocity cosmology. [ABSTRACT FROM AUTHOR]

Sterile neutrinos in the mass range of a few keV are candidates for both cold and warm dark matter. An admixture of a heavy neutrino mass eigenstate to the electron neutrino would result in a minuscule distortion-a kink-in a β-decay spectrum. In this paper we show that a wavelet transform is a very powerful shape analysis method to detect this signature. For a tritium source strength, similar to what is expected from the KATRIN experiment, a statistical sensitivity to active-to-sterile neutrino mixing down to sin2θ = 10-6 (90% C.L.) can be obtained after three years of measurement time. It is demonstrated that the wavelet approach is largely insensitive to systematic effects that result in smooth spectral modifications. To make full use of this analysis technique a high-resolution measurement (FWHM of ~ 100 eV) of the tritium β-decay spectrum is required. [ABSTRACT FROM AUTHOR]

Axions and similar very weakly interacting particles are increasingly compelling candidates for the cold dark matter of the Universe. Having very low mass and being produced nonthermally in the early universe, axions feature extremely high occupation numbers. It has been suggested that this leads to the formation of a Bose-Einstein condensate with potentially significant impact on observation and direct detection experiments. In this paper we aim to clarify that if Bose-Einstein condensation occurs for light and very weakly interacting dark matter particles, it does not happen in thermal equilibrium but is described by a far from equilibrium state. In particular we point out that the dynamics is characterized by two very different time scales, such that condensation occurs on a much shorter time scale than full thermalization. [ABSTRACT FROM AUTHOR]

Bayesian model comparison penalizes models with more free parameters that are allowed to vary over a wide range, and thus offers the most robust method to decide whether some given data require new parameters. In this paper, we ask a simple question: do current cosmological data require extensions of the simplest single-field inflation models? Specifically, we calculate the Bayesian evidence of a totally anticorrelated isocurvature perturbation and a running spectral index of the scalar curvature perturbation. These parameters are motivated by recent claims that the observed temperature anisotropy of the cosmic microwave background on large angular scales is too low to be compatible with the simplest inflation models. Both a subdominant, anticorrelated cold dark matter isocurvature component and a negative running index succeed in lowering the large-scale temperature power spectrum. We show that the introduction of isocurvature perturbations is disfavored, whereas that of the running spectral index is only moderately favored, even when the BICEP2 data are included in the analysis without any foreground subtraction. [ABSTRACT FROM AUTHOR]

We introduce a set of minimal simplified models for dark matter interactions with the Standard Model, connecting the two sectors via either a scalar or pseudoscalar particle. These models have a wider regime of validity for dark matter searches at the LHC than the effective field theory approach, while still allowing straightforward comparison to results from noncollider dark matter detection experiments. Such models also motivate dark matter searches in multiple correlated channels. In this paper, we constrain scalar and pseudoscalar simplified models with direct and indirect detection experiments, as well as from existing LHC searches with missing energy plus tops, bottoms, or jets, using the exact loop-induced coupling with gluons. This calculation significantly affects key differential cross sections at the LHC, and must be properly included. We make connections with the Higgs sector, and conclude with a discussion of future searches at the LHC. [ABSTRACT FROM AUTHOR]

In this paper, we show that positron data from AMS seem to rule out the explanation of the ARCADE isotropic radio background excess in terms of self-annihilating dark matter. In earlier works it was found that leptonic annihilation channels of light dark matter provide a good fit to the excess due to synchrotron emission of the final state particles. However, limits on the self-annihilation cross section derived from the positron data of AMS now severely constrain light self-annihilating dark matter and cross sections below that of a thermal relic are already tested for leptonic annihilation channels. Combining these two results, we conclude that an explanation of the excess in the radio background in terms of self-annihilating dark matter is excluded. [ABSTRACT FROM AUTHOR]

Recently, several works have investigated the coupling to matter in ghost-free massive bigravity and multigravity and a new effective coupling to matter has been proposed. In this paper we clarify some confusion on the existence and the implications of a ghost above the strong coupling scale. We confirm that the standard constraint which is otherwise typically present in this type of theories disappears on generic backgrounds as soon as this new coupling is considered. This implies the reemergence of the Boulware-Deser ghost. Nevertheless the absence of ghost in the decoupling limit implies that the cutoff scale (if identified with the scale at which the ghost enters) is higher than the strong coupling scale. Therefore there is a valid interesting region of applicability for these couplings at scales below the cutoff. [ABSTRACT FROM AUTHOR]

As a first step to generalize the structure of loop quantum cosmology to the theories with the spacetime dimension other than four, the isotropic model of loop quantum cosmology in 2 + 1 dimension is studied in this paper. We find that the classical big bang singularity is again replaced by a quantum bounce in the model. The similarities and differences between the (2 + 1)-dimensional model and the (3 + 1)- dimensional one are also discussed. [ABSTRACT FROM AUTHOR]

Understanding the relation between underlying matter distribution and biased tracers such as galaxies or dark matter halos is essential to extract cosmological information from ongoing or future galaxy redshift surveys. At sufficiently large scales such as the baryon acoustic oscillation (BAO) scale, a standard approach for the bias problem on the basis of the perturbation theory (PT) is to assume the "local bias" model in which the density field of biased tracers is deterministically expanded in terms of matter density field at the same position. The higher-order bias parameters are then determined by combining the power spectrum with higher-order statistics such as the bispectrum. As is pointed out by recent studies, however, nonlinear gravitational evolution naturally induces nonlocal bias terms even if initially starting only with purely local bias. As a matter of fact, previous works showed that the second-order nonlocal bias term, which corresponds to the gravitational tidal field, is important to explain the characteristic scale-dependence of the bispectrum. In this paper we extend the nonlocal bias term up to third order, and investigate whether the PT-based model including nonlocal bias terms can simultaneously explain the power spectrum and the bispectrum of simulated halos in N-body simulations. The bias renormalization procedure ensures that only one additional term is necessary to be introduced to the power spectrum as a next-to-leading order correction, even if third-order nonlocal bias terms are taken into account. We show that the power spectrum, including density and momentum, and the bispectrum between halo and matter in N-body simulations can be simultaneously well explained by the model including up to third-order nonlocal bias terms at k≲0.1h/Mpc. Also, the results are in a good agreement with theoretical predictions of a simple coevolution picture, although the agreement is not perfect. These trend can be found for a wide range of halo mass, 0.7≲Mhalo[1013M☉/h]≲20 at various redshifts, 0≤z≤1. These demonstrations clearly show a failure of the local bias model even at such large scales, and we conclude that nonlocal bias terms should be consistently included in order to accurately model statistics of halos. [ABSTRACT FROM AUTHOR]

One working hypothesis on which analyses of cosmological data are based is the zero ensemble mean hypothesis, which is related to the statistical homogeneity of cosmological perturbations. This hypothesis, however, should be tested by observational data in the current era of precision cosmology. Herein, we test the hypothesis by analyzing recent, foreground-reduced cosmic miσowave background (CMB) maps, combining the spherical harmonic coefficients of the masked CMB temperature anisotropies in such a way that the combined variables can be treated as statistically independent samples. We find evidence against the zero mean hypothesis in two particular ranges of multipoles, with significance levels of 2.5σ and 3. lσ in the multipole ranges of ϵ ≈ 61-86 and 213-256, respectively, for both the Planck and Wilkinson Miσowave Anisotropy Probe maps. The latter signal is consistent with our previous result found by using brute-force Monte Carlo simulations. However, within the method employed in this paper we conclude that the zero mean hypothesis is consistent with the current CMB data on the basis of Stouffer's weighted Z statistics, which takes multiple testing into account. [ABSTRACT FROM AUTHOR]

The High Altitude Water Cherenkov (HAWC) observatory is a wide field-of-view detector sensitive to gamma rays of 100 GeV to a few hundred TeV. Located in central Mexico at 19° North latitude and 4100 m above sea level, HAWC will observe gamma rays and cosmic rays with an array of water Cherenkov detectors. The full HAWC array is scheduled to be operational in Spring 2015. In this paper, we study the HAWC sensitivity to the gamma-ray signatures of high-mass (multi-TeV) dark matter annihilation. The HAWC observatory will be sensitive to diverse searches for dark matter annihilation, including annihilation from extended dark matter sources, the diffuse gamma-ray emission from dark matter annihilation, and gamma-ray emission from nonluminous dark matter subhalos. Here we consider the HAWC sensitivity to a subset of these sources, including dwarf galaxies, the M31 galaxy, the Virgo cluster, and the Galactic center. We simulate the HAWC response to gamma rays from these sources in several well-motivated dark matter annihilation channels. If no gamma-ray excess is observed, we show the limits HAWC can place on the dark matter cross section from these sources. In particular, in the case of dark matter annihilation into gauge bosons, HAWC will be able to detect a narrow range of dark matter masses to cross sections below thermal. HAWC should also be sensitive to nonthermal cross sections for masses up to nearly 1000 TeV. The constraints placed by HAWC on the dark matter cross section from known sources should be competitive with current limits in the mass range where HAWC has similar sensitivity. HAWC can additionally explore higher dark matter masses than are currently constrained. [ABSTRACT FROM AUTHOR]

In a companion paper Detmold et al. [Phys. Rev. D 90, 114506 (2014)], lattice field theory methods are used to show that in two-color, two-flavor QCD there are stable nuclear states in the spectrum. As a commonly studied theory of composite dark matter, this motivates the consideration of possible nuclear physics in this and other composite dark sectors. In this work, early Universe cosmology and indirect detection signatures are explored for both symmetric and asymmetric dark matter, highlighting the unique features that arise from considerations of dark nuclei and associated dark nuclear processes. The present day dark matter abundance may be composed of dark nucléons and/or dark nuclei, where the latter are generated through dark nucleosynthesis. For symmetric dark matter, indirect detection signatures are possible from annihilation, dark nucleosynthesis, and dark nuclear capture and we present a novel explanation of the Galactic center gamma ray excess based on the latter. For asymmetric dark matter, dark nucleosynthesis may alter the capture of dark matter in stars, allowing for captured particles to be processed into nuclei and ejected from the star through dark nucleosynthesis in the core. Notably, dark nucleosynthesis realizes a novel mechanism for indirect detection signals of asymmetric dark matter from regions such as the Galactic center, without having to rely on a symmetric dark matter component. [ABSTRACT FROM AUTHOR]

In this paper we compute all contributions to the muon magnetic moment stemming from several 3-3-1 models, namely, minimal 331, 331 with right-handed neutrinos, 331 with heavy neutral leptons, 331 with charged exotic leptons, 331 economical and 331 with two Higgs triplets. Further, we exploit the complementarity among current electroweak, dark matter and collider constraints to outline the relevant parameter space of the models capable of explaining the anomaly. Lastly, assuming that the experimental anomaly has been otherwise resolved, we derive robust Iσ bounds using the current and projected measurements. [ABSTRACT FROM AUTHOR]

The discovery of a void of size ~200h-1 Mpc and average density contrast of ~-0.1 aligned with the cold spot direction has been recently reported. It has been argued that, although the first-order integrated Sachs-Wolfe (ISW) effect of such a void on the cosmic microwave background is small, the second-order Rees-Sciama (RS) contribution exceeds this by an order of magnitude and can entirely explain the observed cold spot temperature profile. In this paper we examine this surprising claim using both an exact calculation with the spherically symmetric Lemaître-Tolman-Bondi metric, and perturbation theory about a background Friedmann-Robertson-Walker metric. We show that both approaches agree well with each other, and both show that the dominant temperature contribution of the postulated void is an unobservable dipole anisotropy. If this dipole is subtracted, we find that the remaining temperature anisotropy is dominated by the linear ISW signal, which is orders of magnitude larger than the second-order RS effect, and that the total magnitude is too small to explain the observed cold spot profile. We calculate the density and size of a void that would be required to explain the cold spot, and show that the probability of existence of such a void is essentially zero in ACDM. We identify the importance of a posteriori selection effects in the identification of the cold spot, but argue that even after accounting for them, a supervoid explanation of the cold spot is always disfavored relative to a random statistical fluctuation on the last scattering surface. [ABSTRACT FROM AUTHOR]

Recent experimental results from the LHC have placed strong constraints on the masses of colored superpartners. The MSSM parameter space is also constrained by the measurement of the Higgs boson mass, and the requirement that the relic density of lightest neutralinos be consistent with observations. Although large regions of the MSSM parameter space can be excluded by these combined bounds, leptophilic versions of the MSSM can survive these constraints. In this paper we consider a scenario in which the requirements of minimal flavor violation, vanishing CP-violation, and mass universality are relaxed, specifically focusing on scenarios with light sleptons. We find a large region of parameter space, analogous to the original bulk region, for which the lightest neutralino is a thermal relic with an abundance consistent with that of dark matter. We find that these leptophilic models are constrained by measurements of the magnetic and electric dipole moments of the electron and muon, and that these models have interesting signatures at a variety of indirect detection experiments. [ABSTRACT FROM AUTHOR]

In this paper we present a new search technique for electroweakinos, the superpartners of electroweak gauge and Higgs bosons, based on final states with missing transverse energy, a photon, and a dilepton pair, ℓ+ℓ- + γ + ...T. Unlike traditional electroweakino searches, which perform best when mχ02,3 - mχ01, mχ± - mχ01 > mZ, our search favors nearly degenerate spectra; degenerate electroweakinos typically have a larger branching ratio to photons, and the cut mℓℓ ≪ mZ effectively removes on shell Z boson backgrounds while retaining the signal. This feature makes our technique optimal for "well-tempered" scenarios, where the dark matter relic abundance is achieved with interelectroweakino splittings of ~ 20-70 GeV. Additionally, our strategy applies to a wider range of scenarios where the lightest neutralinos are almost degenerate, but only make up a subdominant component of the dark matter--a spectrum we dub well forged. Focusing on bino-Higgsino admixtures, we present optimal cuts and expected efficiencies for several benchmark scenarios. We find bino-Higgsino mixtures with mχ02,3 ≲ 190??GeV and mχ02,3 - mχ01 ≅ 30 GeV can be uncovered after roughly 600 fb-1 of luminosity at the 14 TeV LHC. Scenarios with lighter states require less data for discovery, while scenarios with heavier states or larger mass splittings are harder to discriminate from the background and require more data. Unlike many searches for supersymmetry, electroweakino searches are one area where the high luminosity of the next LHC run, rather than the increased energy, is crucial for discovery. [ABSTRACT FROM AUTHOR]

The possibility of sending the LISA Pathfinder spacecraft through the Sun-Earth saddle point following its nominal mission around LI has now been studied for a few years. The principal motivation for doing so is to search for anomalous gravity gradients predicted by several alternative theories of gravity. In turn, these have originally been motivated by the dark matter problem, and predict deviations from General Relativity in regions of low acceleration. All signal estimates to date have ignored the presence of the spacecraft mass distribution and its self-gravity, on the basis that the gravitational field due to Sun and Earth is larger than that due to the spacecraft itself, for any realistic saddle point fly-by distances. In this paper, we show that at least for one of the theoretical frameworks, Quasilinear Modified Newtonian Dynamics (QMOND), the presence of the local mass distribution cannot be ignored. Using simplified representations of the spacecraft mass distribution, we demonstrate that internal self-gravity, in particular internal gravitational gradients, can enhance the QMOND signals by more than 3 orders of magnitude. These preliminary results indicate that the parameter space accessible to LISA Pathfinder may be significantly larger than previously thought. We find further that the details of the matter distribution as well as of the trajectory can affect the expected signal shape, due to the coupling between internal and external gravitational fields and field gradients. We hope that this work will motivate a more comprehensive investigation of the effect, not just in QMOND, but also in the context of other theoretical frameworks. [ABSTRACT FROM AUTHOR]

In this paper, we study the prospects for determining the nature of neutrinos in the context of a supersymmetric B-L extension of the standard model by using dark matter indirect detection signals and bounds on Neff from the cosmic microwave background data. The model contains two new dark matter candidates whose dominant annihilation channels produce more neutrinos than neutralino dark matter in the minimal supersymmetric standard model. The photon and neutrino counts may then be used to discriminate between the two models. If the dark matter comes from the B-L sector, its indirect signals and impact on the cosmic microwave background can shed light on the nature of the neutrinos. When the light neutrinos are of Majorana type, the indirect neutrino signal from the Sun and the galactic center may show a prompt neutrino box-feature, as well as an earlier cut-off in both neutrino and gamma ray energy spectra. When the light neutrinos are of Dirac type, their contribution to the effective number of neutrinos Neff is at a detectable level. [ABSTRACT FROM AUTHOR]

The varying speed of light theory is controversial. It succeeds in explaining some cosmological problems, but, on the other hand, it is excluded by mainstream physics because it will shake the foundation of physics. In the present paper, we devote ourselves to testing whether the speed of light is varying from the observational data of the type la supernova, baryon acoustic oscillation, observational H(z) data, and cosmic microwave background. We select the common form c(t) = c0an(t) with the contribution of dark energy and matter, where c0 is the current value of speed of light and n is a constant, and consequently we construct a varying speed of light dark energy model (VSLDE). The combined observational data show a trivial constraint n = -0.0033 ± 0.0045 at 68.3% confidence level, which indicates that the speed of light may be a constant with high significance. By reconstructing the time variable c(t), we find that the speed of light almost has no variation for redshift z < 10-1. For high-z observations, they are more sensitive to the VSLDE model, but the variation of speed of light is only in order of 10-2. We also introduce the geometrical diagnostic Om(z) to show the difference between the VSLDE and A cold dark matter (ACDM) models. The result shows that the current data make it difficult to differentiate them. All the results show that the observational data favor the constant speed of light. [ABSTRACT FROM AUTHOR]

The correlation between the invisible Higgs branching ratio (Binvh) versus dark matter (DM) direct detection cross section (σSIp) in Higgs portal singlet fermion DM (SFDM) or vector DM (VDM) models is usually presented in the effective field theory (EFT) framework. In this paper, we derive the explicit expressions for this correlation within UV completions of SFDM and VDM models with Higgs portals, and we discuss the limitations of the EFT approach. We show that there are at least two additional hidden parameters in sSIp in the UV completions: the singletlike scalar mass m2 and its mixing angle α with the SM Higgs boson (h). In particular, if the singletlike scalar is lighter than the SM Higgs boson (m2 < mhcosα/√1+cos²α), the collider bound becomes weaker than the one based on EFT. [ABSTRACT FROM AUTHOR]

Coy dark matter removes the tension between the traditional WIMP paradigm of dark matter and the latest exclusion bounds from direct detection experiments. In this paper we present a leptophilic coy dark matter model that, on top of explaining the spatially extended 1-5 GeV ?-ray excess detected at the galactic center, reconciles the measured anomalous magnetic moment of muon with the corresponding standard model prediction. The annihilation channel of dark matter is ???tt with the dark matter mass m?=9.43(0.52+.063stat)(±1.2sys)??GeV given by best-fit of the ?-ray excess. Fitting the measured anomalous magnetic moment of the muon requires instead a pseudoscalar mediator with a minimal mass ma=12-3+7 GeV. [ABSTRACT FROM AUTHOR]

The search for sharp features in the gamma-ray spectrum is a promising approach to identify a signal from dark matter annihilations over the astrophysical backgrounds. In this paper we investigate the generation of gamma-ray lines and internal bremsstrahlung signals in a toy model where the dark matter particle is a real scalar that couples to a lepton and an exotic fermion via a Yukawa coupling. We show that the Fermi-LAT and H.E.S.S. searches for linelike spectral features severely constrain regions of the parameter space where the scalar dark matter is thermally produced. Finally, we also discuss the complementarity of the searches for sharp spectral features with other indirect dark matter searches, as well as with direct and collider searches. [ABSTRACT FROM AUTHOR]