Thermal decoupling and the smallest subhalo mass in dark matter models with Sommerfeld-enhanced annihilation rates

We consider dark matter consisting of weakly interacting massive particles (WIMPs) and revisit in detail its thermal evolution in the early universe, with a particular focus on models where the annihilation rate is enhanced by the Sommerfeld effect. After chemical decoupling, or freeze-out, dark matter no longer annihilates but is still kept in local thermal equilibrium due to scattering events with the much more abundant standard model particles. During kinetic decoupling, even these processes stop to be effective, which eventually sets the scale for a small-scale cutoff in the matter density fluctuations. Afterwards, the WIMP temperature decreases more quickly than the heat bath temperature, which causes dark matter to reenter an era of annihilation if the cross-section is enhanced by the Sommerfeld effect. Here, we give a detailed and self-consistent description of these effects. As an application, we consider the phenomenology of simple leptophilic models that have been discussed in the literature and find that the relic abundance can be affected by as much two orders of magnitude or more. We also compute the mass of the smallest dark matter subhalos in these models and find it to be in the range of about 10^{-10} to 10 solar masses; even much larger cutoff values are possible if the WIMPs couple to force carriers lighter than about 100 MeV. We point out that a precise determination of the cutoff mass allows to infer new limits on the model parameters, in particular from gamma-ray observations of galaxy clusters, that are highly complementary to existing constraints from g-2 or beam dump experiments.Comment: minor changes to match published versio

Free streaming in mixed dark matter

Free streaming in a \emph{mixture} of collisionless non-relativistic dark matter (DM) particles is studied by implementing methods from the theory of multicomponent plasmas. The mixture includes Fermionic, condensed and non condensed Bosonic particles decoupling in equilibrium while relativistic, heavy non-relativistic thermal relics (WIMPs), and sterile neutrinos that decouple \emph{out of equilibrium} when they are relativistic. The free-streaming length $\lambda_{fs}$ is obtained from the marginal zero of the gravitational polarization function, which separates short wavelength Landau-damped from long wavelength Jeans-unstable \emph{collective} modes. At redshift $z$ we find $\frac{1}{\lambda^2_{fs}(z)}= \frac{1}{(1+z)} \big[\frac{0.071}{\textrm{kpc}} \big]^2 \sum_{a}\nu_a g^{2/3}_{d,a}({m_a}/{\mathrm{keV}})^2 I_a$,where $0\leq \nu_a \leq 1$ are the \emph{fractions} of the respective DM components of mass $m_a$ that decouple when the effective number of ultrarelativistic degrees of freedom is $g_{d,a}$, and $I_a$ only depend on the distribution functions at decoupling, given explicitly in all cases. If sterile neutrinos produced either resonantly or non-resonantly that decouple near the QCD scale are the \emph{only} DM component,we find $\lambda_{fs}(0) \simeq 7 \mathrm{kpc} (\mathrm{keV}/m)$ (non-resonant), $\lambda_{fs}(0) \simeq 1.73 \mathrm{kpc} (\mathrm{keV}/m)$ (resonant).If WIMPs with $m_{wimp} \gtrsim 100 \mathrm{GeV}$ decoupling at $T_d \gtrsim 10 \mathrm{MeV}$ are present in the mixture with $\nu_{wimp} \gg 10^{-12}$,$\lambda_{fs}(0) \lesssim 6.5 \times 10^{-3} \mathrm{pc}$ is \emph{dominated} by CDM. If a Bose Einstein condensate is a DM component its free streaming length is consistent with CDM because of the infrared enhancement of the distribution function.Comment: 19 pages, 2 figures. More discussions same conclusions and results. Version to appear in Phys. Rev.

Alterations of nocturnal activity in rats following subchronic oral administration of the neurotoxin 1-trichloromethyl-1,2,3,4-tetrahydro-β-carboline

1-Trichloromethyl-1,2,3,4-tetrahydro-β-carboline (TaClo) is neurotoxic when administered to the brain and alters motor behaviour following intraperitoneal administration. We have assessed the long-term effects of oral TaClo administration on nocturnal motor behaviour in rats. Two groups of rats received TaClo orally at a dose of either 0.2 or 0.4 mg/kg twice daily for 7 weeks. The control group was given saline. No change in locomotor activity was observed 4–9 days after the end of the 7-week administration of TaClo. In addition, the spontaneous motor activity was altered dose-dependently 9 months after oral TaClo administration, with an increase in the low-dose TaClo group and a decrease in the high-dose group. Oral administration of TaClo in rats may be useful in investigating the hypothesis that in Parkinson’s disease, an unknown pathogenic factor crossing the intestinal mucosa barrier can induce neurodegenerative processes eventually affecting the entire brain

Dark Matter signals from Draco and Willman 1: Prospects for MAGIC II and CTA

The next generation of ground-based Imaging Air Cherenkov Telescopes (IACTs) will play an important role in indirect dark matter searches. In this article, we consider two particularly promising candidate sources for dark matter annihilation signals, the nearby dwarf galaxies Draco and Willman 1, and study the prospects of detecting such a signal for the soon-operating MAGIC II telescope system as well as for the planned installation of CTA, taking special care of describing the experimental features that affect the detectional prospects. For the first time in such a study, we fully take into account the effect of internal bremsstrahlung, which has recently been shown to considerably enhance, in some cases, the gamma-ray flux at the high energies where Atmospheric Cherenkov Telescopes operate, thus leading to significantly harder annihilation spectra than traditionally considered. While the detection of the spectral features introduced by internal bremsstrahlung would constitute a smoking gun signature for dark matter annihilation, we find that for most models the overall flux still remains at a level that will be challenging to detect unless one adopts rather (though by no means overly) optimistic astrophysical assumptions about the distribution of dark matter in the dwarfs.Comment: 10 pages, 4 figures, minor changes, matches the published version (JCAP

TeV cosmic-ray proton and helium spectra in the myriad model

Recent measurements of cosmic ray proton and helium spectra show a hardening above a few hundreds of GeV. This excess is hard to understand in the framework of the conventional models of Galactic cosmic ray production and propagation. We propose here to explain this anomaly by the presence of local sources (myriad model). Cosmic ray propagation is described as a diffusion process taking place inside a two-zone magnetic halo. We calculate the proton and helium fluxes at the Earth between 50 GeV and 100 TeV. Improving over a similar analysis, we consistently derive these fluxes by taking into account both local and remote sources for which a unique injection rate is assumed. We find cosmic ray propagation parameters compatible with B/C measurements and for which the proton and helium spectra remarkably agree with the PAMELA and CREAM measurements over four decades in energy.Comment: 5 pages, 3 figure

From (p)reheating to nucleosynthesis

This article gives a brief qualitative description of the possible evolution of the early Universe between the end of an inflationary epoch and the end of Big Bang nucleosynthesis. After a general introduction, establishing the minimum requirements cosmologists impose on this cosmic evolutionary phase, namely, successful baryogenesis, the production of cosmic dark matter, and successful light-element nucleosynthesis, a more detailed discussion on some recent developments follows. This latter includes the physics of preheating, the putative production of (alternative) dark matter, and the current status of Big Bang nucleosynthesis.Comment: 18 pages, 6 figures, to be published in "Classical and Quantum Gravity", article based on a talk presented at ``The Early Universe and Cosmological Observations: a Critical Review'', Cape Town, July 200

Gamma Lines without a Continuum: Thermal Models for the Fermi-LAT 130 GeV Gamma Line

Recent claims of a line in the Fermi-LAT photon spectrum at 130 GeV are suggestive of dark matter annihilation in the galactic center and other dark matter-dominated regions. If the Fermi feature is indeed due to dark matter annihilation, the best-fit line cross-section, together with the lack of any corresponding excess in continuum photons, poses an interesting puzzle for models of thermal dark matter: the line cross-section is too large to be generated radiatively from open Standard Model annihilation modes, and too small to provide efficient dark matter annihilation in the early universe. We discuss two mechanisms to solve this puzzle and illustrate each with a simple reference model in which the dominant dark matter annihilation channel is photonic final states. The first mechanism we employ is resonant annihilation, which enhances the annihilation cross-section during freezeout and allows for a sufficiently large present-day annihilation cross section. Second, we consider cascade annihilation, with a hierarchy between p-wave and s-wave processes. Both mechanisms require mass near-degeneracies and predict states with masses closely related to the dark matter mass; resonant freezeout in addition requires new charged particles at the TeV scale.Comment: 17 pages, 8 figure

Atropselective syntheses of (-) and (+) rugulotrosin A utilizing point-to-axial chirality transfer

Chiral, dimeric natural products containing complex structures and interesting biological properties have inspired chemists and biologists for decades. A seven-step total synthesis of the axially chiral, dimeric tetrahydroxanthone natural product rugulotrosin A is described. The synthesis employs a one-pot Suzuki coupling/dimerization to generate the requisite 2,2'-biaryl linkage. Highly selective point-to-axial chirality transfer was achieved using palladium catalysis with achiral phosphine ligands. Single X-ray crystal diffraction data were obtained to confirm both the atropisomeric configuration and absolute stereochemistry of rugulotrosin A. Computational studies are described to rationalize the atropselectivity observed in the key dimerization step. Comparison of the crude fungal extract with synthetic rugulotrosin A and its atropisomer verified that nature generates a single atropisomer of the natural product.P50 GM067041 - NIGMS NIH HHS; R01 GM099920 - NIGMS NIH HHS; GM-067041 - NIGMS NIH HHS; GM-099920 - NIGMS NIH HH

Two photon annihilation of Kaluza-Klein dark matter

We investigate the fermionic one-loop cross section for the two photon annihilation of Kaluza-Klein (KK) dark matter particles in a model of universal extra dimensions (UED). This process gives a nearly mono-energetic gamma-ray line with energy equal to the KK dark matter particle mass. We find that the cross section is large enough that if a continuum signature is detected, the energy distribution of gamma-rays should end at the particle mass with a peak that is visible for an energy resolution of the detector at the percent level. This would give an unmistakable signature of a dark matter origin of the gamma-rays, and a unique determination of the dark matter particle mass, which in the case studied should be around 800 GeV. Unlike the situation for supersymmetric models where the two-gamma peak may or may not be visible depending on parameters, this feature seems to be quite robust in UED models, and should be similar in other models where annihilation into fermions is not helicity suppressed. The observability of the signal still depends on largely unknown astrophysical parameters related to the structure of the dark matter halo. If the dark matter near the galactic center is adiabatically contracted by the central star cluster, or if the dark matter halo has substructure surviving tidal effects, prospects for detection look promising.Comment: 17 pages, 3 figures; slightly revised versio

The detection of sub-solar mass dark matter halos

Dark matter halos of sub-solar mass are the first bound objects to form in cold dark matter theories. In this article, I discuss the present understanding of "microhalos'', their role in structure formation, and the implications of their potential presence, in the interpretation of dark matter experiments.Comment: 18 pages, 7 figures. Invited contribution to NJP Focus Issue on "Dark Matter and Particle Physics