Taking into account spins, we classify all two-body non-relativistic Dark Matter annihilation channels to the allowed polarization states of Standard Model particles, computing the energy spectra of the stable nal-state particles relevant for indirect DM detection. We study the DM masses, annihilation channels and cross sections that can reproduce the PAMELA indications of an e + excess consistently with the PAMELA p data and the ATIC/PPB-BETS e + +e data. From the PAMELA data alone, two solutions emerge: (i) either the DM particles that annihilate into W;Z;h must be heavier than about 10 TeV or (ii) the DM must annihilate only into leptons. Thus in both cases a DM particle compatible with the PAMELA excess seems to have quite unexpected properties. The solution (ii) implies a peak in the e + +e

Model-independent implications of the e , p cosmic ray spectra on properties of Dark Matter (updated including AMS 2013 data)

It is commonly assumed that the energy density of the Universe was dominated by radiation between reheating after inflation and the onset of matter domination 54,000 years later While the abundance of light elements indicates that the Universe was radiation dominated during Big Bang Nucleosynthesis (BBN), there is scant evidence that the Universe was radiation dominated prior to BBN It is therefore possible that the cosmological history was more complicated, with deviations from the standard radiation domination during the earliest epochs Indeed, several interesting proposals regarding various topics such as the generation of dark matter, matter-antimatter asymmetry, gravitational waves, primordial black holes, or microhalos during a nonstandard expansion phase have been recently made In this paper, we review various possible causes and consequences of deviations from radiation domination in the early Universe - taking place either before or after BBN - and the constraints on them, as they have been discussed in the literature during the recent years

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The first three seconds: A Review of Possible Expansion Histories of the early Universe

Stars as laboratories for fundamental physics

We show that the electron recoil excess around 2 keV claimed by the Xenon Collaboration can be fitted by dark matter (DM) or DM-like particles having a fast component with velocity of order $\ensuremath{\sim}01$ Those particles cannot be part of the cold DM halo of our Galaxy, so we speculate about their possible nature and origin, such as fast-moving DM subhalos, semiannihilations of DM and relativistic axions produced by a nearby axion star Feasible new physics scenarios must accommodate exotic DM dynamics and unusual DM properties

Dark Matter and the XENON1T electron recoil excess

Author(s): Ren, T; Kwa, A; Kaplinghat, M; Yu, HB | Abstract: Galactic rotation curves exhibit diverse behavior in the inner regions while obeying an organizing principle; i.e., they can be approximately described by a radial acceleration relation or the modified Newtonian dynamics phenomenology. We analyze the rotation curve data from the SPARC sample and explicitly demonstrate that both the diversity and uniformity are naturally reproduced in a hierarchical structure formation model with the addition of dark matter self-interactions. The required concentrations of the dark matter halos are fully consistent with the concentration-mass relation predicted by the Planck cosmological model. The inferred stellar mass-to-light (3.6 μm) ratios scatter around 0.5 Mâ™/Lâ™, as expected from population synthesis models, leading to a tight radial acceleration relation and a baryonic Tully-Fisher relation. The inferred stellar-halo mass relation is consistent with the expectations from abundance matching. These results provide compelling arguments in favor of the idea that the inner halos of galaxies are thermalized due to dark matter self-interactions.

Reconciling the Diversity and Uniformity of Galactic Rotation Curves with Self-Interacting Dark Matter

The freeze-out of dark matter (DM) depends on the evolution of the DM temperature. The DM temperature does not have to follow the standard model one, when the elastic scattering is not sufficient to maintain the kinetic equilibrium. We study the temperature evolution of the semiannihilating DM, where a pair of the DM particles annihilate into one DM particle and another particle coupled to the standard model sector. We find that the kinetic equilibrium is maintained solely via semiannihilation until the last stage of the freeze-out. After the freeze-out, semiannihilation converts the mass deficit to the kinetic energy of DM, which leads to nontrivial evolution of the DM temperature. We argue that the DM temperature redshifts like radiation as long as the DM self-interaction is efficient. We dub this novel temperature evolution as self-heating. Notably, the structure formation is suppressed at subgalactic scales like keV-scale warm DM but with GeV-scale self-heating DM if the self-heating lasts roughly until the matter-radiation equality. The long duration of the self-heating requires the large self-scattering cross section, which in turn flattens the DM density profile in inner halos. Consequently, self-heating DM can be a unified solution to apparent failures of cold DM to reproduce the observed subgalactic scale structure of the Universe.

Self-Heating Dark Matter via Semiannihilation.

It was recently pointed out that semiannihilating dark matter (DM) may experience a novel temperature evolution dubbed as self-heating. Exothermic semiannihilation converts the DM mass to the kinetic energy. This yields a unique DM temperature evolution, ${T}_{\ensuremath{\chi}}\ensuremath{\propto}1/a$, in contrast to ${T}_{\ensuremath{\chi}}\ensuremath{\propto}1/{a}^{2}$ for free-streaming nonrelativistic particles. Self-heating continues as long as self-scattering sufficiently redistributes the energy of DM particles. In this paper, we study the evolution of cosmological perturbations in self-heating DM. We find that sub-GeV self-heating DM leaves a cutoff on the subgalactic scale of the matter power spectrum when the self-scattering cross section is ${\ensuremath{\sigma}}_{\mathrm{self}}/{m}_{\ensuremath{\chi}}\ensuremath{\sim}\mathcal{O}(1)\text{ }\text{ }{\mathrm{cm}}^{2}/\mathrm{g}$. Then we present a particle physics realization of the self-heating DM scenario. The model is based on recently proposed strongly interacting massive particles with pionlike particles in a QCD-like sector. Pionlike particles semiannihilate into an axionlike particle, which is thermalized with dark radiation. The dark radiation temperature is smaller than the standard model temperature, evading the constraint from the effective number of neutrino degrees of freedom. It is easily realized when the dark sector is populated from the standard model sector through a small coupling.

Self-heating of strongly interacting massive particles

We study self-interacting dark matter (SIDM) scenarios, where the s-wave self-scattering cross section almost saturates the Unitarity bound. Such self-scattering cross sections are singly parameterized by the dark matter mass, and are featured by strong velocity dependence in a wide range of velocities. They may be indicated by observations of dark matter halos in a wide range of masses, from Milky Way’s dwarf spheroidal galaxies to galaxy clusters. We pin down the model parameters that saturates the Unitarity bound in well-motivated SIDM models: the gauged Lμ − Lτ model and composite asymmetric dark matter model. We discuss implications and predictions of such model parameters for cosmology like the H0 tension and dark-matter direct-detection experiments, and particle phenomenology like the beam-dump experiments.

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Maximally self-interacting dark matter: models and predictions

Exothermic scatterings of dark matter (DM) produce DM particles with significant kick velocities inside DM halos. In collaboration with DM self-interaction, the excess kinetic energy of the produced DM particles is distributed to the others, which self-heats the DM particles as a whole. The DM self-heating is efficient towards the halo center, and the heat injection is used to enhance the formation of a uniform density core inside halos. The effect of DM self-heating is expected to be more significant in smaller halos for two reasons: 1) the exothermic cross section times the relative velocity, $\left\langle\sigma_{\rm exo}v_{\rm rel}\right\rangle$, is constant; 2) and the ratio of the injected heat to the velocity dispersion squared gets larger towards smaller halos. For the first time, we quantitatively investigate the core formation from DM self-heating for halos in a wide mass range ($10^{9}$-$10^{15}\,{\rm M}_\odot$) using the gravothermal fluid formalism. Notably, we demonstrate that the core formation is sharply escalating towards smaller halos by taking the self-heating DM (i.e., DM that semi-annihilates and self-interacts) as an example. We show that the sharp escalation of core formation may cause a tension in simultaneously explaining the observed central mass deficit of Milky Way satellites, and field dwarf/low surface brightness spiral galaxies. While the details of the self-heating effect may differ among models, we expect that the sharp halo-mass dependence of the core formation is a general feature of exothermic DM.

Escalating core formation with dark matter self-heating

The latest $\mathrm{Lyman}\text{\ensuremath{-}}\ensuremath{\alpha}$ forest data severely constrain the conventional warm dark matter solution to small-scale issues in the cold dark matter paradigm. It has been also reported that unconstrained astrophysical processes may address the issues. In response to this situation, we revisit the decaying dark matter solution to the issues, discussing possible signatures to discriminate decaying dark matter from astrophysical processes as a solution to small-scale issues. We consider an axinolike particle (ALPino) decaying into an axionlike particle (ALP) and gravitino with the lifetime around the age of the Universe. The ALPino mass is sub-PeV and slightly ($\mathrm{\ensuremath{\Delta}}m/m\ensuremath{\sim}{10}^{\ensuremath{-}4}$) larger than the gravitino mass, and thus the dark matter abundance does not alter virtually after the ALPino decays. On the other hand, the gravitino produced from the ALPino decay obtains a kick velocity of $\ensuremath{\sim}30\text{ }\text{ }\mathrm{km}/\mathrm{s}$, which is sufficiently larger than a circular velocity of dwarf galaxies to impact their dark matter distributions. The $\mathrm{Lyman}\text{\ensuremath{-}}\ensuremath{\alpha}$ forest constraints are relieved since only a small fraction ($\ensuremath{\sim}10%$) of dark matter experiences the decay at that time. Decaying dark matter is thus promoted to a viable solution to small-scale issues. The ALPino relic abundance is determined predominantly by the decay of the lightest ordinary supersymmetric particle. The monochromatic ALP emission from the ALPino decay is converted to $\ensuremath{\sim}50\text{ }\text{ }\mathrm{GeV}$ photon under the Galactic magnetic field. The morphology of the gamma-ray flux shows a distinctive feature of the model when compared to decaying dark matter that directly decays into photons. Once detected, such distinctive signals discriminate the decaying dark matter solution to small-scale issues from unconstrained astrophysical processes.

Hee Jung Kim

Papers

Self-Heating Dark Matter via Semiannihilation.

Self-heating of strongly interacting massive particles

Maximally self-interacting dark matter: models and predictions

Escalating core formation with dark matter self-heating

Decaying axinolike dark matter: Discriminative solution to small-scale issues