Search

We consider models of pure gravity mediation in which scalar mass universality is imposed at the grand unified scale and gaugino masses are generated through loops. The minimal model requires a very restricted range for tanβ ≈ 2-3 and scalar masses (set by the gravitino mass) of order 300 TeV-1.5 PeV in order to obtain a Higgs mass near 126 GeV. Here we augment the minimal model with one or more sets of vector multiplets (either a 10 and 10 pair or one or more 5 and 5 pairs). If coupled to the minimal supersymmetric standard model Higgs, these allow for radiative electroweak symmetry breaking over a significantly larger range of tanβ ≈2-40 and can fit the Higgs mass with much smaller values of the gravitino mass. In these models, the lightest supersymmetric particle is often the bino, and in order to satisfy the relic density constraint, the bino must be nearly degenerate with either the wino or gluino. In the models considered here, bino gluino coannihilations determine the relic density and since the two are nearly degenerate, LHC limits on the gluino mass are greatly relaxed allowing light relatively gravitinos and gluino masses well within the reach of the LHC. [ABSTRACT FROM AUTHOR]

We consider the effect of the coupled variations of fundamental constants on the nucleon magnetic moment. The nucleon g-factor enters into the interpretation of the measurements of variations in the fine-structure constant, α, in both the laboratory (through atomic clock measurements) and in astrophysical systems (e.g. through measurements of the 21 cm transitions). A null result can be translated into a limit on the variation of a set of fundamental constants, that is usually reduced to α. However, in specific models, particularly unification models, changes in α are always accompanied by corresponding changes in other fundamental quantities such as the QCD scale, ΛQCD. This work tracks the changes in the nucleon g-factors induced from changes in ΛQCD and the light quark masses. In principle, these coupled variations can improve the bounds on the variation of α by an order of magnitude from existing atomic clock and astrophysical measurements. Unfortunately, the calculation of the dependence of g-factors on fundamental parameters is notoriously model-dependent. [ABSTRACT FROM AUTHOR]

We extend our previous studies of the neutrino fluxes expected from neutralino LSP annihilations inside the Sun to include variants of the minimal supersymmetric extension of the Standard Model (MSSM) with squark, slepton and gaugino masses constrained to be universal at the GUT scale, but allowing one or two nonuniversal supersymmetry breaking parameters contributing to the Higgs masses (NUHM 1,2). As in the constrained MSSM (CMSSM) with universal Higgs masses, there are large regions of the NUHM parameter space where the LSP density inside the Sun is not in equilibrium, so that the annihilation rate may be far below the capture rate, and there are also large regions where the capture rate is not dominated by spin-dependent LSP-proton scattering. The spectra possible in the NUHM are qualitatively similar to those in the CMSSM. We calculate neutrino-induced muon fluxes above a threshold energy of 10 GeV, appropriate for the IceCube/DeepCore detector, for points where the NUHM yields the correct cosmological relic density for representative choices of the NUHM parameters. We find that the IceCube/ DeepCore detector can probe regions of the NUHM parameter space in addition to analogues of the focus point strip and the tip of the coannihilation strip familiar from the CMSSM. These include regions with enhanced Higgsino-gaugino mixing in the LSP composition, that occurs where neutralino mass eigenstates cross over. On the other hand, rapid-annihilation funnel regions in general yield neutrino fluxes that are unobservably small. [ABSTRACT FROM AUTHOR]

We consider the signatures of a domain wall produced in the spontaneous symmetry breaking involving a dilaton-like scalar field coupled to electromagnetism. Domains on either side of the wall exhibit slight differences in their respective values of the fine-structure constant, alpha. If such a wall is present within our Hubble volume, absorption spectra at large redshifts may or may not provide a variation in alpha relative to the terrestrial value, depending on our relative position with respect to the wall. This wall could resolve the "contradiction'' between claims of a variation of alpha based on Keck/Hires data and of the constancy of alpha based on VLT data. We derive the properties of the wall and the parameters of the underlying microscopic model required to reproduce the possible spatial variation of alpha. We discuss the constraints on the existence of the low-energy domain wall and describe its observational implications concerning the variation of the fundamental constants. [ABSTRACT FROM AUTHOR]

We consider the direct s-channel gravitational production of dark matter during the reheating process. Independent of the identity of the dark matter candidate or its nongravitational interactions, the gravitational process is always present and provides a minimal production mechanism. During reheating, a thermal bath is quickly generated with a maximum temperature Tmax, and the temperature decreases as the inflaton continues to decay until the energy densities of radiation and inflaton oscillations are equal, at TRH. During these oscillations, s-channel gravitational production of dark matter occurs. We show that the abundance of dark matter (fermionic or scalar) depends primarily on the combination T4max/TRHM³P. We find that a sufficient density of dark matter can be produced over a wide range of dark matter masses: from 1 GeV to 1 ZeV. [ABSTRACT FROM AUTHOR]

The reported spatial variation in the fine structure constant at high redshift, if physical, could be due to the presence of dilatonic domains, and one or more domain walls inside our horizon. An absorption spectrum of an object in a different domain from our own would be characterized by a different value of α. We show that while a single-wall solution is statically comparable to a dipole fit, and is a big improvement over a weighted mean (despite adding three parameters), a two-wall solution is a far better fit (despite adding three parameters over the single-wall solution). We derive a simple model accounting for the two domain wall solution. The goodness of these fits is, however, dependent on the extra random error which was argued to account for the large scatter in most of the data. When this error is omitted, all the above solutions are poor fits to the data. When included, the solutions that exhibit a spatial dependence agree with the data much more significantly than the standard model; however, the standard model itself is not a terrible fit to the data, having a p value of ~20%. [ABSTRACT FROM AUTHOR]

Unlike minimal SU(5), SO(10) provides a straightforward path towards gauge coupling unification by modifying the renormalization group evolution of the gauge couplings above some intermediate scale which may also be related to the seesaw mechanism for neutrino masses. Unification can be achieved for several different choices of the intermediate gauge group below the SO(10) breaking scale. In this work, we consider in detail the possibility that SO(10) unification may also provide a natural dark matter candidate, stability being guaranteed by a leftover Z2 symmetry. We systematically examine the possible intermediate gauge groups which allow a nondegenerate, fermionic, Standard Model singlet dark matter candidate while at the same time respecting gauge coupling unification. Our analysis is done at the two-loop level. Surprisingly, despite the richness of SO(10), we find that only two models survive the analysis of phenomenological constraints, which include suitable neutrino masses, proton decay, and reheating. [ABSTRACT FROM AUTHOR]

We study a minimal extension of the Standard Model where a scalar field is coupled to the right-handed neutrino responsible for the seesaw mechanism for neutrino masses. In the absence of other couplings, below 8 TeV the scalar A has a unique decay mode A → νν, ν being the physical observed light neutrino state. Above 8 TeV (11 TeV), the 3-body (4-body) decay modes dominate. Imposing constraints on neutrino masses mν from atmospheric and solar experiments implies a long lifetime for A, much larger than the age of the Universe, making it a natural dark matter candidate. Its lifetime can be as large as 1029 seconds, and its signature below 8 TeV would be a clear monochromatic neutrino signal, which can be observed by ANTARES or IceCube. Under certain conditions, the scalar A may be viewed as a Goldstone mode of a complex scalar field whose vacuum expectation value generates the Majorana mass for νR. In this case, we expect the dark matter scalar to have a mass ≲ 10 GeV. [ABSTRACT FROM AUTHOR]

We discuss the proton lifetime in pure gravity mediation models with nonuniversal Higgs soft masses. Pure gravity mediation olfers a simple framework for studying SU(5) grand unified theories with a split supersymmetrylike spectra. We find that for much of the parameter space gauge coupling unification is quite good leading to rather long lifetimes for the proton. However, for m3/2 ~ 60 TeV and tan β ~ 4, for which gauge coupling unification is also good, the proton lifetime is short enough that it could be in reach of future experiments. [ABSTRACT FROM AUTHOR]

Pure gravity mediation, with two free parameters, is a minimalistic approach to supergravity models, yet it is capable of incorporating radiative electroweak symmetry breaking, a Higgs mass in agreement with the experimental measurement, without violating any phenomenological constraints. The model may also contain a viable dark matter candidate in the form of a wino. Here, we extend the minimal model by allowing the g term to be a free parameter equivalent to allowing the two Higgs soft masses, m1 and m2, to differ from other scalar masses, which are set by the gravitino mass. In particular, we examine the region of parameter space where μ « m3/2, in which case the Higgsino becomes the lightest supersymmetric particle and a dark matter candidate. We also consider a generalization of pure gravity mediation that incorporates a Peccei-Quinn symmetry which determines the g term dynamically. In this case we show that the dark matter may either be in the form of an axion and/or a neutralino and that the lightest supersymmetric particle may be either a wino, bino, or Higgsino. [ABSTRACT FROM AUTHOR]

We propose a minimal model framework for physics below the Planck scale with the following features: (i) it is based on no-scale supergravity, as favored in many string compactifications, (ii) it incorporates Starobinsky-like inflation, and hence is compatible with constraints from the Planck satellite, (iii) the inflaton may be identified with a singlet field in a seesaw model for neutrino masses, providing an efficient scenario for reheating and leptogenesis, (iv) supersymmetry breaking occurs with an arbitrary scale and a cosmological constant that vanishes before radiative corrections, and (v) regions of the model parameter space are compatible with all LHC, Higgs boson, and dark matter constraints. [ABSTRACT FROM AUTHOR]

We consider the phenomenological consequences of fixing compactification moduli. In the simplest Kachru-Kallosh-Linde-Trivedi constructions, stabilization of internal dimensions is rather soft: weak scale masses for moduli are generated, and are of order m&sgr; ∼ m3/2. As a consequence one obtains a pattern of soft supersymmetry breaking masses found in gravity and/or anomaly mediated supersymmetry breaking (AMSB) models. These models may lead to destabilization of internal dimensions in the early universe, unless the Hubble constant during inflation is very small. Fortunately, strong stabilization of compactified dimensions can be achieved by a proper choice of the superpotential (e.g., in the Kallosh- Linde model with a racetrack superpotential). This allows for a solution of the cosmological moduli problem and for a successful implementation of inflation in supergravity. We show that strong moduli stabilization leads to a very distinct pattern of soft supersymmetry breaking masses. In general, we find that soft scalar masses remain of order the gravitino mass, while gaugino masses nearly vanish at the tree level; i.e., they are of order m23/2/mσ. Radiative corrections generate contributions to gaugino masses reminiscent of AMSB models and a decoupled spectrum of scalars reminiscent of split supersymmetry. This requires a relatively large gravitino mass [ ∼ 0(100) TeV], resolving the cosmological gravitino problem and problems with tachyonic staus in AMSB models [ABSTRACT FROM AUTHOR]

We investigate the recently proposed class of chaotic inflation models in supergravity with an arbitrary inflaton potential V(φ). These models are extended to include matter fields in the visible sector and we employ a mechanism of supersymmetry breaking based on a particular phenomenological version of the KKLT mechanism (the KL model). We describe specific features of reheating in this class of models and show how one can solve the cosmological moduli and gravitino problems in this context. [ABSTRACT FROM AUTHOR]

We explore a nuclear physics resolution to the discrepancy between the predicted standard big-bang nucleosynthesis (BBN) abundance of 7Li and its observational determination in metal-poor stars. The theoretical 7Li abundance is 3-4 times greater than the observational values, assuming the baryon-to-photon ratio, ηwmap, determined by WMAP. The 7Li problem could be resolved within the standard BBN picture if additional destruction of A=7 isotopes occurs due to new nuclear reaction channels or upward corrections to existing channels. This could be achieved via missed resonant nuclear reactions, which is the possibility we consider here. We find some potential candidate resonances which can solve the lithium problem and specify their required resonant energies and widths. For example, a 1- or 2- excited state of 10C sitting at approximately 15.0 MeV above its ground state with an effective width of order 10 keV could resolve the 7Li problem; the existence of this excited state needs experimental verification. Other examples using known states include 7Be+t→10B(18.80??MeV), and 7Be+d→9B(16.71??MeV). For all of these states, a large channel radius (a>10??fm) is needed to give sufficiently large widths. Experimental determination of these reaction strengths is needed to rule out or confirm these nuclear physics solutions to the lithium problem. [ABSTRACT FROM AUTHOR]

We consider a spin-3/2 particle and show that with a Planck reduced coupling, we can obtain a sufficiently long lifetime making the spin-3/2 particle a good dark matter candidate. We show that this dark matter candidate can be produced during inflationary reheating through the scattering of Standard Model particles. The relic abundance as determined by Planck and other experimental measurements is attained for reasonable values of the reheating temperature TRH≳108 GeV. We consider two possible gauge invariant couplings to the extended Standard Model. We find a large range of masses are possible which respect the experimental limits on its decay rate. We expect smoking-gun signals in the form of a monochromatic photon with a possible monochromatic neutrino, which can be probed in the near future in IceCube and other indirect detection experiments. [ABSTRACT FROM AUTHOR]

No-scale supergravity provides a successful framework for Starobinsky-like inflation models. Two classes of models can be distinguished depending on the identification of the inflaton with the volume modulus, T (C models), or a matterlike field, (WZ models). When supersymmetry is broken, the inflationary potential may be perturbed, placing restrictions on the form and scale of the supersymmetry breaking sector. We consider both types of inflationary models in the context of high-scale supersymmetry. We further distinguish between models in which the gravitino mass is below and above the inflationary scale. We examine the mass spectra of the inflationary sector. We also consider, in detail, mechanisms for leptogenesis for each model when a right-handed neutrino sector, used in the seesaw mechanism to generate neutrino masses, is employed. In the case of C models, reheating occurs via an inflaton decay to two Higgs bosons. However, there is a direct decay channel to the lightest right-handed neutrino which leads to nonthermal leptogenesis. In the case of WZ models, in order to achieve reheating, we associate the matterlike inflaton with one of the right-handed sneutrinos whose decay to the lightest right-handed neutrino simultaneously reheats the Universe and generates the baryon asymmetry through leptogenesis. [ABSTRACT FROM AUTHOR]

We consider both "bottom-up" and "top-down" approaches to the origin of gauge kinetic mixing. We focus on the possibilities for obtaining kinetic mixings e which are consistent with experimental constraints and are much smaller than the naive estimates (e~10-2-10-1) at the one-loop level. In the bottom-up approach, we consider the possible suppression from multiloop processes. Indeed we argue that kinetic mixing through gravity alone, requires at least six loops and could be as large as ~10-13. In the top-down approach we consider embedding the Standard Model and a U(1)X in a single grand-unified gauge group as well as the mixing between Abelian and non-Abelian gauge sectors. [ABSTRACT FROM AUTHOR]

We present a minimal SU(2,1)/SU(2)×U(1) no-scale model that unifies modulus fixing, Starobinsky-like inflation, an adjustable scale for supersymmetry breaking, and the possibility of a small cosmological constant, a.k.a. dark energy. [ABSTRACT FROM AUTHOR]

We compare dark matter production from the thermal bath in the early universe with its direct production through the decay of the inflaton. We show that even if dark matter does not possess a direct coupling with the inflaton, Standard Model loop processes may be sufficient to generate the correct relic abundance. [ABSTRACT FROM AUTHOR]

We show that R² gravity coupled conformally to scalar fields is equivalent to the real bosonic sector of SU(N, 1)/SU(N) × U(1) no-scale supergravity, where the conformal factor can be identified with the Kähler potential, and we review the construction of Starobinsky-like models of inflation within this framework. [ABSTRACT FROM AUTHOR]

In the first stages of inflationary reheating, the temperature of the radiation produced by inflaton decays is typically higher than the commonly defined reheating temperature TRH∼(ΓϕMP)1/2 where Γϕ is the inflaton decay rate. We consider the effect of particle production at temperatures at or near the maximum temperature attained during reheating. We show that the impact of this early production on the final particle abundance depends strongly on the temperature dependence of the production cross section. For ⟨σv⟩∼Tn/Mn+2, and for n<6, any particle produced at Tmax is diluted by the later generation of entropy near TRH. This applies to cases such as gravitino production in low scale supersymmetric models (n=0) or NETDM models of dark matter (n=2). However, for n≥6 the net abundance of particles produced during reheating is enhanced by over an order of magnitude, dominating over the dilution effect. This applies, for instance to gravitino production in high scale supersymmetry models where n=6. [ABSTRACT FROM AUTHOR]

Big bang nucleosynthesis (BBN) describes the production of the lightest nuclides via a dynamic interplay among the four fundamental forces during the first seconds of cosmic time. A brief overview of the essentials of this physics is given, and new calculations presented of light-element abundances through 6Li and 7Li, with updated nuclear reactions and uncertainties including those in the neutron lifetime. Fits are provided for these results as a function of baryon density and of the number of neutrino flavors Nμ. Recent developments are reviewed in BBN, particularly new, precision Planck cosmic microwave background (CMB) measurements that now probe the baryon density, helium content, and the effective number of degrees of freedom Neff. These measurements allow for a tight test of BBN and cosmology using CMB data alone. Our likelihood analysis convolves the 2015 Planck data chains with our BBN output and observational data. Adding astronomical measurements of light elements strengthens the power of BBN. A new determination of the primordial helium abundance is included in our likelihood analysis. New D/H observations are now more precise than the corresponding theoretical predictions and are consistent with the standard model and the Planck baryon density. Moreover, D/H now provides a tight measurement of Nμ when combined with the CMB baryon density and provides a 2σ upper limit Nμ<3.2. The new precision of the CMB and D/H observations together leaves D/H predictions as the largest source of uncertainties. Future improvement in BBN calculations will therefore rely on improved nuclear cross-section data. In contrast with D/H and 4He, 7Li predictions continue to disagree with observations, perhaps pointing to new physics. This paper concludes with a look at future directions including key nuclear reactions, astronomical observations, and theoretical issues. [ABSTRACT FROM AUTHOR]

We investigate the effect of a variation of fundamental constants on primordial element production in big bang nucleosynthesis (BBN). We focus on the effect of a possible change in the nucleon-nucleon interaction on nuclear reaction rates involving the A=5 (5Li and 5He) and A=8 (8Be) unstable nuclei. The reaction rates for ³He(d,p)4He and ³H(d,n)4He are dominated by the properties of broad analog resonances in 5He and 5Li compound nuclei, respectively. While the triple alpha process 4He(αα,γ)12C is normally not effective in BBN, its rate is very sensitive to the position of the "Hoyle state" and could in principle be drastically affected if 8Be were stable during BBN. The nuclear properties (resonance energies in 5He and 5Li nuclei, and the binding energies of 8Be and D) are all computed in a consistent way using a microscopic cluster model. The n(p,γ)d, ³He(d,p)4He, ³H(d,n)4He, and 4He(αα,γ)12C1 reaction rates are subsequently calculated as a function of the nucleon-nucleon interaction that can be related to the fundamental constants. We found that the effect of the variation of constants on the ³He(d,p)4He, ³H(d,n)4He, and 4He(αα,γ)12C reaction rates is not sufficient to induce a significant effect on BBN, even if 8Be was stable. In particular, no significant production of carbon by the triple alpha reaction is found when compared to standard BBN. Finally, we complement our earlier work on the effect of coupled variation of fundamental constants inducing variations of the binding energy of deuterium, the Fermi constant, and the neutron-proton mass difference, that affect the weak rates and the n(p,γ)d, A=2 bottleneck reaction. [ABSTRACT FROM AUTHOR]

A recent global fit to the constrained minimal supersymmetric extension of the Standard Model incorporating current constraints on supersymmetry, including missing transverse energy searches at the LHC, BR(Bs → μ+μ-) and the direct XENON100 search for dark matter, favors points towards the end of the stau-neutralino (ι~l-χ) coannihilation strip with relatively large m1/2 and 10 ≲ tanß ≲ 40 and points in the H/A rapid-annihilation funnel with tan?ß ~ 50. The coannihilation points typically have mιl-mx ≲ GeV, and a significant fraction, including the most-favored point, has mιl-mx < mι. In such a case, the ι1 lifetime would be so long that the ιl would be detectable as a long-lived massive charged particle that may decay inside or outside the apparatus. We show that CMSSM scenarios close to the tip of the coannihilation strip for tan ß ≲ 40 are already excluded by LHC searches for massive charged particles and discuss the prospects for their detection in the CMS and ATLAS detectors via time-of-flight measurements, anomalous heavy ionization or decays into one or more soft charged particles. [ABSTRACT FROM AUTHOR]

Residual late-time dark matter particle annihilations during and after big-bang nucleosynthesis may alter the predicted cosmological abundances of the light elements. Within the constrained minimal supersymmetric extension of the standard model with a neutralino as the lightest supersymmetric particle, we find negligible effects on the abundances of deuterium, 3He, 4He, and 7Li predicted by homogeneous big-bang nucleosynthesis, but potentially a large enhancement in the predicted abundance of 6Li. This enhancement may be as much as 2 orders of magnitude in the focus-point WMAP strip and in the coannihilation and funnel regions for large tanβ for small m1/2, and the effect is still significant at large m1/2-However, the potential 6Li enhancement is negligible in the part of the coannihilation strip for tanβ = 10 that survives the latest LHC constraints. A similar enhancement of the 6Li abundance may also be found in a model with common, nonuniversal Higgs masses (the NUHM1). [ABSTRACT FROM AUTHOR]

It has been argued that supergravity models of inflation with vanishing sound speeds, cs, lead to an unbounded growth in the production rate of gravitinos. We consider several models of inflation to delineate the conditions for which cs=0. In models with unconstrained superfields, we argue that the mixing of the Goldstino and inflatino in a time-varying background prevents the uncontrolled production of the longitudinal modes. This conclusion is unchanged if there is a nilpotent field associated with supersymmetry breaking with constraint S2=0, i.e., (s)Goldstino-less models. Models with a second orthogonal constraint, S(Φ-¯Φ)=0, where Φ is the inflaton superfield, which eliminates the inflatino, may suffer from the overproduction of gravitinos. However, we point out that these models may be problematic if this constraint originates from a UV Lagrangian, as this may require using higher derivative operators. These models may also exhibit other pathologies, such as cs>1, which are absent in theories with the single constraint or unconstrained fields. [ABSTRACT FROM AUTHOR]

We perform a systematic analysis of dark matter production during postinflationary reheating. Following the period of exponential expansion, the inflaton begins a period of damped oscillations as it decays. These oscillations and the evolution of temperature of the thermalized decay products depend on the shape of the inflaton potential V (F). We consider potentials of the form, F k. Standard matter-dominated oscillations occur for k = 2. In general, the production of dark matter may depend on either (or both) the maximum temperature after inflation, or the reheating temperature, where the latter is defined when the Universe becomes radiation dominated. We show that dark matter production is sensitive to the inflaton potential and depends heavily on the maximum temperature when k > 2 . We also consider the production of dark matter with masses larger than the reheating temperature. [ABSTRACT FROM AUTHOR]

We propose a model where a long-lived pseudoscalar EeV particle can be produced with sufficient abundance so as to account for the cold dark matter density, despite having a Planck mass suppressed coupling to the thermal bath. Connecting this state to a hidden sterile neutrino sector through derivative couplings, induced by higher dimensional operators, allows one to account for light neutrino masses while having a lifetime that can be much larger than the age of the Universe. Moreover, the same derivative coupling accounts for the production of dark matter in the very first instant of the reheating. Given the sensitivity of the IceCube and ANITA collaborations, we study the possible signatures of such a model in the form of ultrahigh-energy cosmic rays in the neutrino sector, and show that such signals could be detected in the near future. [ABSTRACT FROM AUTHOR]

We revisit the limits on R -parity violation in the minimal supersymmetric standard model. In particular, we focus on the high-scale supersymmetry scenario in which all the sparticles are in excess of the inflationary scale of approximately 1013 GeV, and thus no sparticles ever come into thermal equilibrium. In this case, the cosmological limits, stemming from the preservation of the baryon asymmetry that have been previously applied for weak-scale supersymmetry, are now relaxed. We argue that even when sparticles are never in equilibrium, R-parity violation is still constrained via higher dimensional operators by neutrino and nucleon experiments and/or insisting on the preservation of a nonzero B - L asymmetry. [ABSTRACT FROM AUTHOR]

Gauge coupling unification and the stability of the Higgs vacuum are among two of the cherished features of low-energy supersymmetric models. Putting aside questions of naturalness, supersymmetry might only be realized in nature at very high energy scales. If this is the case, the preservation of gauge coupling unification and the stability of the Higgs vacuum would certainly require new physics, but it need not necessarily be at weak scale energies. New physics near the unification scale could, in principle, ensure grand unification, while new physics below 1010 GeV could ensure the stability of the Higgs vacuum. Surprisingly however, we find that in the context of a supersymmetric SO(10) grand unified theory, gauge coupling unification and the Higgs vacuum stability, when taken in conjunction with existing phenomenological constraints, require the presence of O(TeV)-scale physics. This weak-scale physics takes the form of a complex scalar SU(2)L triplet with zero hypercharge, originating from the 210 of SO(10). [ABSTRACT FROM AUTHOR]

We consider the effects of R-parity violation due to the inclusion of a bilinear μ'LHu superpotential term in high-scale supersymmetric models with an EeV scale gravitino as dark matter. Although the typical phenomenological limits on this coupling (e.g., due to lepton number violation and the preservation of the baryon asymmetry) are relaxed when the supersymmetric mass spectrum is assumed to be heavy (in excess of the inflationary scale of 3×1013 GeV), the requirement that the gravitino be sufficiently long lived so as to account for the observed dark matter density, leads to a relatively strong bound on μ'≲20 GeV. The dominant decay channels for the longitudinal component of the gravitino are Z, W±l±, and hν. To avoid an excess neutrino signal in IceCube, our limit on μ' is then strengthened to μ'≲50 keV. When the bound is saturated, we find that there is a potentially detectable flux of monochromatic neutrinos with EeV energies. [ABSTRACT FROM AUTHOR]

We generalize models invoking a spin-2 particle as a mediator between the dark sector and the standard model. We show that a massive spin-2 messenger can efficiently play the role of a portal between the two sectors. The dark matter is then produced via a freeze-in mechanism during the reheating epoch. In a large part of the parameter space, production through the exchange of a massive spin-2 mediator dominates over processes involving a graviton with Planck suppressed couplings. We perform a systematic analysis of such models for different values of the spin-2 mass relative to the maximum and the final temperature attained at reheating. [ABSTRACT FROM AUTHOR]

We consider inflation and supersymmetry breaking in the context of a minimal model of supersymmetry in which the only "low" energy remnant of supersymmetry is the gravitino with a mass of order an EeV. In this theory, the supersymmetry breaking scale is above the inflaton mass, m≃3×1013 GeV, as are all sfermion and gaugino masses. In particular, for a no-scale formulation of Starobinsky-like inflation using the volume modulus T, we show that inflation can be accommodated even when the supersymmetry breaking scale is very large. Reheating is driven through a gravitational coupling to the two Higgs doublets and is enhanced by the large µ-parameter. This leads to gravitino cold dark matter where the mass is constrained to be in the range 0.1 EeV≲m3/2≲1000 EeV. [ABSTRACT FROM AUTHOR]