Search

A dark QCD sector is a relatively minimal extension of the Standard Model (SM) that admits Dark Matter (DM) candidates, but requires no portal to the visible sector beyond gravitational interactions: a "nightmare scenario"for DM detection. We consider a secluded dark sector containing a single flavor of light, vector-like dark quark gauged under (N). In the large-N limit, this single-flavor theory becomes highly predictive, generating two DM candidates whose masses and dynamics are described by few parameters: a light quark-antiquark bound state, the dark analog of the η' meson, and a heavy bound state of N quarks, the dark analog of the Δ++ baryon. We show that the latter may freeze-in with an abundance independent of the confinement scale, forming DM-like relics for N ≲ 10, while the former may generate DM via cannibalization and freeze-out. We study the interplay of this two-component DM system, and determine the characteristic ranges of the confinement scale, dark-visible sector temperature ratio, and N that admit non-excluded DM, once effects of self-interaction constraints and bounds on effective degrees of freedom at the BBN and CMB epochs are included.

We explore the dark matter phenomenology of a weak-scale right-handedneutrino in the context of a Two Higgs Doublet Model. The expected signal atdirect detection experiments is different from the usual spin-independent andspin-dependent classification since the scattering with quarks depends on thedark matter spin. The dark matter relic density is set by thermal freeze-outand in the presence of non-standard cosmology, where an Abelian gauge symmetryis key for the dark matter production mechanism. We show that such symmetryallows us to simultaneously address neutrino masses and the flavor problempresent in general Two Higgs Doublet Model constructions. Lastly, we outlinethe region of parameter space that obeys collider, perturbative unitarity anddirect detection constraints.

The evaporation of primordial black holes with a mass in the $1\ {\rmgram}\lesssim M_{\rm PBH}\lesssim$1000 kg range can lead to the production ofdark matter particles of almost any mass in the range $0.1\ {\rm MeV}\lesssimm_{\rm DM}\lesssim 10^{18}$ GeV with the right relic density at very earlytimes, $\tau\lesssim 10^{-10}$ s. We calculate, as a function of the primordialblack holes mass and initial abundance, the combination of dark matter particlemasses and number of effective dark degrees of freedom leading to the rightabundance of dark matter today, whether or not evaporation stops around thePlanck scale. In addition, since black hole evaporation can also lead to theproduction of a baryon asymmetry, we calculate where dark matter production andbaryogenesis can concurrently happen, under a variety of assumptions:baryogenesis via grand unification boson decay, via leptogenesis, or viaasymmetric co-genesis of dark matter and ordinary matter. Finally, we commenton possible ways to test this scenario.

We discuss the cosmology of models in which the standard model Yukawa couplings depend on scalar field(s), often referred to as flavons. We find that thermal corrections of the flavon potential tend to decrease the Yukawa couplings, providing an important input to model-building. Working in the specific framework of Froggatt-Nielsen models, we compute the abundance of flavons in the early universe generated both via freeze-in and from coherent oscillations induced by thermal corrections to their potential, and discuss constraints on flavon models from cosmology. We find that cosmology places important constraints on theories containing flavons even for regions of parameter space inaccessible to collider searches.

We discuss the phenomenology of an MeV-scale Dirac fermion coupled to theStandard Model through a dark photon with kinetic mixing with theelectromagnetic field. We compute the dark matter relic density and explore theinterplay of direct detection and accelerator searches for dark photons. Weshow that precise measurements of the temperature and polarization powerspectra of the Cosmic Microwave Background Radiation lead to stringentconstraints, leaving a small window for the thermal production of this MeV darkmatter candidate. The forthcoming MeV gamma-ray telescope e-ASTROGAM will offerimportant and complementary opportunities to discover dark matter particleswith masses below 10 MeV. Lastly, we discuss how a late-time inflation episodeand freeze-in production could conspire to yield the correct relic densitywhile being consistent with existing and future constraints.

If the dark matter is produced in the early universe prior to Big Bangnucleosynthesis, a modified cosmological history can drastically affect theabundance of relic dark matter particles. Here, we assume that an additionalspecies to radiation dominates at early times, causing the expansion rate at agiven temperature to be larger than in the standard radiation-dominated case.We demonstrate that, if this is the case, dark matter production via freeze-in(a scenario when dark matter interacts very weakly, and is dumped in the earlyuniverse out of equilibrium by decay or scattering processes involvingparticles in the thermal bath) is dramatically suppressed. We illustrate andquantitatively and analytically study this phenomenon for three differentparadigmatic classes of freeze-in scenarios. For the frozen-in dark matterabundance to be as large as observations, couplings between the dark matter andvisible-sector particles must be enhanced by several orders of magnitude. Thissheds some optimistic prospects for the otherwise dire experimental andobservational outlook of detecting dark matter produced by freeze-in.

We consider a modification to the standard cosmological history consisting ofintroducing a new species $\phi$ whose energy density red-shifts with the scalefactor $a$ like $\rho_\phi \propto a^{-(4+n)}$. For $n>0$, such a red-shift isfaster than radiation, hence the new species dominates the energy budget of theuniverse at early times while it is completely negligible at late times. Ifequality with the radiation energy density is achieved at low enoughtemperatures, dark matter can be produced as a thermal relic during the newcosmological phase. Dark matter freeze-out then occurs at higher temperaturescompared to the standard case, implying that reproducing the observed abundancerequires significantly larger annihilation rates. Here, we point out acompletely new phenomenon, which we refer to as $\textit{relentless}$ darkmatter: for large enough $n$, unlike the standard case where annihilation endsshortly after the departure from thermal equilibrium, dark matter particleskeep annihilating long after leaving chemical equilibrium, with a significantdepletion of the final relic abundance. Relentless annihilation occurs for $n\geq 2$ and $n \geq 4$ for s-wave and p-wave annihilation, respectively, and itthus occurs in well motivated scenarios such as a quintessence with a kinationphase. We discuss a few microscopic realizations for the new cosmologicalcomponent and highlight the phenomenological consequences of our calculationsfor dark matter searches.

We present a comprehensive review of keV-scale sterile neutrino Dark Matter, collecting views and insights from all disciplines involved - cosmology, astrophysics, nuclear, and particle physics - in each case viewed from both theoretical and experimental/observational perspectives. After reviewing the role of active neutrinos in particle physics, astrophysics, and cosmology, we focus on sterile neutrinos in the context of the Dark Matter puzzle. Here, we first review the physics motivation for sterile neutrino Dark Matter, based on challenges and tensions in purely cold Dark Matter scenarios. We then round out the discussion by critically summarizing all known constraints on sterile neutrino Dark Matter arising from astrophysical observations, laboratory experiments, and theoretical considerations. In this context, we provide a balanced discourse on the possibly positive signal from X-ray observations. Another focus of the paper concerns the construction of particle physics models, aiming to explain how sterile neutrinos of keV-scale masses could arise in concrete settings beyond the Standard Model of elementary particle physics. The paper ends with an extensive review of current and future astrophysical and laboratory searches, highlighting new ideas and their experimental challenges, as well as future perspectives for the discovery of sterile neutrinos.

Dark matter (DM) with sizeable self-interactions mediated by a light species offers a compelling explanation of the observed galactic substructure; furthermore, the direct coupling between DM and a light particle contributes to the DM annihilation in the early universe. If the DM abundance is due to a dark particle-antiparticle asymmetry, the DM annihilation cross-section can be arbitrarily large, and the coupling of DM to the light species can be significant. We consider the case of asymmetric DM interacting via a light (but not necessarily massless) Abelian gauge vector boson, a dark photon. In the massless dark photon limit, gauge invariance mandates that DM be multicomponent, consisting of positive and negative dark ions of different species which partially bind in neutral dark atoms. We argue that a similar conclusion holds for light dark photons; in particular, we establish that the multi-component and atomic character of DM persists in much of the parameter space where the dark photon is sufficiently light to mediate sizeable DM self-interactions. We discuss the cosmological sequence of events in this scenario, including the dark asymmetry generation, the freeze-out of annihilations, the dark recombination and the phase transition which gives mass to the dark photon. We estimate the effect of self-interactions in DM haloes, taking into account this cosmological history. We place constraints based on the observed ellipticity of large haloes, and identify the regimes where DM self-scattering can affect the dynamics of smaller haloes, bringing theory in better agreement with observations. Moreover, we estimate the cosmological abundance of dark photons in various regimes, and derive pertinent bounds.