If dark matter is embedded in a non-trivial dark sector, it may annihilate and decay to lighter dark-sector states which subsequently decay to the Standard Model. Such scenarios - with annihilation followed by cascading dark-sector decays - can explain the apparent excess GeV gamma-rays identified in the central Milky Way, while evading bounds from dark matter direct detection experiments. Each 'step' in the cascade will modify the observable signatures of dark matter annihilation and decay, shifting the resulting photons and other final state particles to lower energies and broadening their spectra. We explore, in a model-independent way, the effect of multi-step dark-sector cascades on the preferred regions of parameter space to explain the GeV excess. We find that the broadening effects of multi-step cascades can admit final states dominated by particles that would usually produce too sharply peaked photon spectra; in general, if the cascades are hierarchical (each particle decays to substantially lighter particles), the preferred mass range for the dark matter is in all cases 20-150 GeV. Decay chains that have nearly-degenerate steps, where the products are close to half the mass of the progenitor, can admit much higher DM masses. We map out the region of mass/cross-section parameter space where cascades (degenerate, hierarchical or a combination) can fit the signal, for a range of final states. In the current work, we study multi-step cascades in the context of explaining the GeV excess, but many aspects of our results are general and can be extended to other applications.
The apparent excess of gamma rays in an extended region in the direction of the galactic center has a spatial distribution and amplitude that are suggestive of dark matter annihilations. If this excess is indeed due to dark matter annihilations, it would indicate the presence of both dark matter and an additional particle beyond the Standard Model that mediates the interactions between the dark matter and Standard Model states. We introduce reference models describing dark matter annihilation to pairs of these new mediators, which decouples the SM-mediator coupling from the thermal annihilatio…
Many particle dark matter models predict that the dark matter undergoes cascade annihilations, i.e. the annihilation products are 4-body final states. In the context of model-independent cascade annihilation models, we study the compatibility of the dark matter interpretation of the Fermi- LAT Galactic center gamma-ray emission with null detections from dwarf spheroidal galaxies. For canonical values of the Milky Way density profile and the local dark matter density, we find that the dark matter interpretation to the Galactic center emission is strongly constrained. However, uncertainties in t…
An excess in gamma-rays from the galactic center observed by the Fermi Large Area Telescope has been proposed as a possible signal of dark matter annihilation. Recently, the Fermi collaboration showed that systematic errors broaden the range of spectral shapes for this excess. We demonstrate fits to this range for (1) flavor-violating annihilations to top-charm pairs and (2) annihilations to on-shell bosonic mediators which decay to Standard Model quarks in a boosted frame. Annihilation of 40 - 100 GeV DM to pairs of spin-1 mediators provide a good fit to the Fermi-LAT spectrum with a normaliz…
The tentative 1.4 TeV excess in the $e^+e^-$ spectrum measured by The DArk Matter Particle Explorer (DAMPE) motivates the possible existence of one or more local dark matter concentrated regions. In particular, Ultra-compact Micro Halos (UCMHs) seeded by large density perturbations in the early universe, allocated within ~0.3 kpc from the solar system, could provide the potential source of electrons and positrons produced from dark matter annihilation, enough to explain the DAMPE signal. Here we consider a UCMH with density profile assuming radial in-fall and explore the preferred halo paramet…
We incorporate Milky Way dark matter halo profile uncertainties, as well as an accounting of diffuse gamma-ray emission uncertainties in dark matter annihilation models for the Galactic Center Extended gamma-ray excess (GCE) detected by the Fermi Gamma Ray Space Telescope. The range of particle annihilation rate and masses expand when including these unknowns. However, two of the most precise empirical determinations of the Milky Way halo's local density and density profile leave the signal region to be in considerable tension with dark matter annihilation searches from combined dwarf galaxy a…
Precision measurements of the positron flux in cosmic ray have revealed an unexplained bump in the spectrum around $E\simeq 300\,\mathrm{GeV}$, not clearly attributable to known astrophysical processes. We propose annihilation of dark matter of mass $m_χ= 780\,\mathrm{GeV}$ with a late-time cross section $σv = 4.63\times 10^{-24}\,\mathrm{cm^3\,s^{-1}}$ as a possible source. The nonmonotonic dependence of the annihilation rate on dark matter velocity, owing to a selective $p$-wave Sommerfeld enhancement, allows such a large signal from the Milky Way without violating corresponding constraints …
A possible dark matter (DM) explanation about the long-standing issue of the Galactic 511 keV line is explored in this paper. For DM cascade annihilations of concern, a DM pair $π_d^{+} π_d^{-}$ annihilates into unstable $π_d^{0} π_d^{0}$, and $π_d^{0}$ decays into $e^+ e^-$ with new interactions suggested by the $^8$Be anomaly. Considering the constraints from the effective neutrino number $N_{\mathrm{eff}}$ and the 511 keV gamma-ray emission, a range of DM is obtained, $11.6 \lesssim m_{π_d^{\pm}} \lesssim 15$ MeV. The typical DM annihilation cross section today is about 3.3 $\times$ $10^{-2…
The two messenger results of the GeV gamma-ray excess at the Galactic center and a probable antiproton excess in the recent AMS-02 observation suggest that these two anomalies may be owing to the same origin --- the dark matter (DM) annihilation into $b \bar b$, while these results seem in tension with the dwarf spheroidal galaxy observations. To give a compatible explanation about it, we consider the pseudoscalar DM particles $S_d^+ S_d^-$ annihilating via $S_d^+ S_d^- \rightarrow S_d^0 S_d^0$, with the process mediated by a new scalar $ϕ$ and $S_d^0$ quickly decaying into $b \bar{b}$. For th…
We calculate the extragalactic diffuse emission originating from the up-scattering of cosmic microwave photons by energetic electrons and positrons produced in particle dark matter annihilation events at all redshifts and in all halos. We outline the observational constraints on this emission and we study its dependence on both the particle dark matter model (including the particle mass and its dominant annihilation final state) and on assumptions on structure formation and on the density profile of halos. We find that for low-mass dark matter models, data in the X-ray band provide the most st…
Evidence for an excess of gamma rays with O(GeV) energy coming from the center of our galaxy has been steadily accumulating over the past several years. Recent studies of the excess in data from the Fermi telescope have cast doubt on an explanation for the excess arising from unknown astrophysical sources. A potential source of the excess is the annihilation of dark matter into standard model final states, giving rise to gamma ray production. The spectrum of the excess is well fit by 30 GeV dark matter annihilating into a pair of b quarks with a cross section of the same order of magnitude as …
We give theoretical predictions for the radio emission of a dark matter candidate annihilating into 2-lepton and 4-lepton final states. We then compare our results with the known radio measurements of the sky temperature as a function of the frequency. In particular, we calculate the radio emission for some dark matter candidates annihilating into intermediate bosons that subsequently decay into a 4-lepton channel with a thermal annihilation cross-section. We show that within the range of frequencies from $20\,{\rm MHz}$ to $5\,{\rm GHz}$, this channel can produce a stronger signature than dir…
We have built a lepton-specific next-to-minimal two-Higgs-doublet-portal vector dark matter model. The vector dark matter in the hidden sector does not directly couple to the visible sector, but instead annihilates into the hidden Higgs bosons which decay through a small coupling into the CP-odd Higgs bosons. In this model, the Galactic center gamma-ray excess is mainly due to the 2-step cascade annihilation with $τ$'s in the final state. The obtained mass of the CP-odd Higgs $A$ in the Galactic center excess fit can explain the muon $g-2$ anomaly at the 2$σ$ level without violating the string…
The process of electron-positron pair production by a photon with subsequent annihilation to a single photon in a strong magnetic field has been studied. The general amplitude has been calculated and the process rate have been found in the low Landau levels approximation (resonant and nonresonant cases). The comparison of resonant and nonresonant cases shows a significant excess of the resonant rate. The polarization of the final photon in a strong magnetic field has also been found. It has been shown that polarizations of the initial and the final photons are independent except for the case o…
The recent high energy electron and positron flux observed by the DAMPE experiment indicates possible excess events near 1.4 TeV. Such an excess may be evidence of dark matter annihilations or decays in a dark matter subhalo that is located close to the solar system. We give here an analysis of this excess from annihilations of Dirac fermion dark matter which is charged under a new $U(1)_X$ gauge symmetry. The interactions between dark matter and the standard model particles are mediated the $U(1)_X$ gauge boson. We show that dark matter annihilations from a local subhalo can explain the exces…
The Milky Way's Galactic Center harbors a gamma-ray excess that is a candidate signal of annihilating dark matter. Dwarf galaxies remain predominantly dark in their expected commensurate emission. In this work we quantify the degree of consistency between these two observations through a joint likelihood analysis. In doing so we incorporate Milky Way dark matter halo profile uncertainties, as well as an accounting of diffuse gamma-ray emission uncertainties in dark matter annihilation models for the Galactic Center Extended gamma-ray excess (GCE) detected by the Fermi Gamma-Ray Space Telescope…
We analyze publicly available Fermi-LAT high-energy gamma-ray data and confirm the existence of clear spectral feature peaked at E=130GeV. Scanning over the Galaxy we identify several disconnected regions where the observed excess originates from. Our best optimized fit is obtained for the central region of Galaxy with a clear peak at 130GeV with local statistical significance 4.5 sigma. The observed excess is not correlated with Fermi bubbles. We compute the photon spectra induced by dark matter annihilations into two and four standard model particles, the latter via two light intermediate st…
Several groups have identified an extended excess of gamma rays over the modeled foreground and background emissions towards the Galactic center (GC) based on observations with the Fermi Large Area Telescope. This excess emission is compatible in morphology and spectrum with a telltale sign from dark matter (DM) annihilation. Here, we present a critical reassessment of DM interpretations of the GC signal in light of the foreground and background uncertainties that some of us recently outlaid in Calore et al. 2014. We find that a much larger number of DM models fits the gamma-ray data than prev…
The presence of an excess gamma-ray signal toward the Galactic center (GC) has now been well established, and is known as the GC excess. Leading explanations for the signal include mis-modeling of the Galactic diffuse emission along the line of sight, an unresolved population of millisecond pulsars, and/or the annihilation of dark matter (DM). Recently, evidence for another excess gamma-ray signal has been reported toward the outer halo of M31. In this work we interpret the excess signals from both the GC and outer halo of M31 in the framework of DM annihilation, and show that the two spectra …
In models of dark matter (DM) with Sommerfeld-enhanced annihilation, where the annihilation rate scales as the inverse velocity, N-body simulations of DM structure formation suggest that the local annihilation signal may be dominated by small, dense, cold subhalos. This contrasts with the usual assumption of a signal originating from the smooth DM halo, with much higher velocity dispersion. Accounting for local substructure modifies the parameter space for which Sommerfeld-enhanced annihilating DM can explain the PAMELA and Fermi excesses. Limits from the inner galaxy and the cosmic microwave …
We show that Q-ball decay in Affleck-Dine baryogenesis models can account for dark matter when the annihilation cross-section is sufficiently enhanced to explain the positron and electron excesses observed by PAMELA, ATIC and PPB-BETS. For Affleck-Dine baryogenesis along a d = 6 flat direction, the reheating temperature is approximately 30 GeV and the Q-ball decay temperature is in the range 10-100 MeV. The LSPs produced by Q-ball decay annihilate down to the observed dark matter density if the cross-section is enhanced by a factor ~ 10^3 relative to the thermal relic cross-section.
Several experiments have reported regions in the TeV sky with an excess of cosmic rays. Here we consider the possibility that the excess cosmic rays are coming from dark matter annihilation in nearby subhalos. We provide motivation for dark matter as the source of the excess and show that dark matter annihilations can naturally produce the cosmic ray anisotropy without the need for exotic dark matter models. We show that viable dark matter explanations of the cosmic ray excess are consistent with current measurements of antiprotons, positrons, and gamma-rays. Additionally, we show that the dar…
An excess of gamma rays at GeV energies has been detected in the Fermi-LAT data. This signal comes from a narrow region around the Galactic Center and has been interpreted as possible evidence for light (30 GeV) dark matter particles. Focussing on the prompt gamma-ray emission, previous works found that the best fit to the data corresponds to annihilations proceeding into b quarks, with a dark matter profile going as r^{-1.2}. We show that this is not the only possible annihilation set-up. More specifically, we show how including the contributions to the gamma-ray spectrum from inverse Compton…
We show that the cosmic-ray positron excess measured by PAMELA and AMS could be induced by Dark Matter annihilations in a local over-density. In such a context leptophilic DM is not needed and good fits to positron data, in agreement with antiproton and gamma-ray measurements, are obtained for DM annihilations to $WW$, $hh$, $ZZ$, $ t \bar t$, $b \bar b$, $q\bar q$ channels. The classic Dark Matter candidates, such as the pure supersymmetric Wino with standard thermal annihilation cross-section, can fit the positron excess, without invoking any additional assumption on Dark Matter properties.
In this paper, we will discuss a specific case that the dark matter particles annihilate into right-handed neutrinos. We calculate the predicted gamma-ray excess from the galactic center and compare our results with the data from the Fermi-LAT. An approximately 10-60 GeV right-handed neutrino with heavier dark matter particle can perfectly explain the observed spectrum. The annihilation cross section $\langle σv \rangle$ falls within the range $0.5$-$4 \times 10^{-26} \text{ cm}^3/\text{s}$, which is roughly compatible with the WIMP annihilation cross section.
The cosmic-ray (CR) $e^\pm$ excess observed by AMS-02 can be explained by dark matter (DM) annihilation. However, the DM explanation requires a large annihilation cross section which is strongly disfavored by other observations, such as the Fermi-LAT gamma-ray observation of dwarf galaxies and the Planck observation of the cosmic microwave background (CMB). Moreover, the DM annihilation cross section required by the CR $e^\pm$ excess is also too large to generate the correct DM relic density with thermal production. In this work we use the Breit-Wigner mechanism with a velocity dependent DM an…
We investigate the possibility of the Z3 scalar singlet model explaining the Fermi galactic centre excess. We find a good fit to the measured spectral excess in the region where the dark matter mass is comparable to the Higgs and the Higgs portal coupling $λ_{HS}\sim 0.04$. This preferred region is consistent with constraints from vacuum stability and current dark matter experiments, and will be discovered or falsified soon by future dark matter direct detection experiment.
Dark matter (DM) annihilations have been widely studied as a possible explanation of excess gamma rays from the galactic center seen by Fermi/LAT. However most such models are in conflict with constraints from dwarf spheroidals. Motivated by this tension, we show that p-wave annihilating dark matter can easily accommodate both sets of observations due to the lower DM velocity dispersion in dwarf galaxies. Explaining the DM relic abundance is then challenging. We outline a scenario in which the usual thermal abundance is obtained through s-wave annihilations of a metastable particle, that event…
We consider dark matter annihilation into a general set of final states of Standard Model particles, including two-body and four-body final states that result from the decay of intermediate states. For dark matter masses ~10-10^5 GeV, we use updated data from Planck and from high gamma-ray experiments such as Fermi-LAT, MAGIC, and VERITAS to constrain the annihilation cross section for each final state. The Planck constraints are the most stringent over the entire mass range for annihilation into light leptons, and the Fermi-LAT constraints are the most stringent for four-body final states up …
The direct measurements of the cosmic electron-positron spectrum around 1 TeV made by DAMPE have induced many theoretical speculations about possible excesses in the data above the standard astrophysical predictions that might have the dark matter (DM) origin. These attempts mainly fall into two categories: i) DM annihilation (or decay) in the Galactic halo producing the broad spectrum excess; ii) DM annihilation in the nearby compact subhalo producing the sharp peak at 1.4 TeV. We investigate the gamma-ray emission accompanying $e^+e^-$ production in DM annihilation, as well as various theore…
Annihilating dark matter (DM) models based on a scalar hidden sector with Higgs portal-like couplings to the Standard Model are considered as a possible explanation for recently observed cosmic ray excesses. Two versions of the model are studied, one with non-thermal DM as the origin of the boost factor and one with Sommerfeld enhancement. In the case of non-thermal DM, four hidden sector scalars which transform under a U(1)_{X} symmetry are added. The heaviest scalars decouple and later decay to DM scalars, so providing the boost factor necessary to explain the present DM annihilation rate. T…
In hidden sector models, dark matter does not directly couple to the particle content of the Standard Model, strongly suppressing rates at direct detection experiments, while still allowing for large signals from annihilation. In this paper, we conduct an extensive study of hidden sector dark matter, covering a wide range of dark matter spins, mediator spins, interaction diagrams, and annihilation final states, in each case determining whether the annihilations are s-wave (thus enabling efficient annihilation in the universe today). We then go on to consider a variety of portal interactions th…
The cosmic electron energy spectrum recently observed by the DAMPE experiment exhibits two interesting features, including a break around 0.9 TeV and a sharp resonance near 1.4 TeV. In this analysis, we propose a dark matter explanation to both exotic features seen by DAMPE. In our model, dark matter annihilates in the galaxy via two different channels that lead to both a narrow resonance spectrum near 1.4 TeV and electron excess events over an extended energy range thus generating the break structure around TeV. The two annihilation channels are mediated by two gauge bosons that interact both…
We show the presence of a potentially detectable gamma-ray line in the Fermi Galactic center excess in light of the secluded (vector) dark matter (DM) model in which the hidden scalar, nearly degenerate with DM in mass, mediates the interaction of the secluded DM with the Standard Model (SM) due to its mixing with the SM Higgs. We find that the parameter region $m_X\in[60, 132]$ GeV can provide a good fit to the Fermi Galactic center gamma-ray excess spectrum, appearing a prominent gamma-ray line with the energy $\in [30, 66]$ GeV. The best fit gives $m_X\simeq m_S \simeq 86$ GeV with a $p$-va…
An excess of gamma rays at GeV energies has been pointed out in the Fermi-LAT data. This signal comes from a narrow region centred around the Galactic center and has been interpreted as possible evidence for light dark matter particles annihilating either into a mixture of leptons-antileptons and b-bbar or into b-bbar only. Focusing on the prompt gamma-ray emission, previous works found that the best fit to the data corresponds to annihilations proceeding predominantly into b-bbar. However, here we show that omitting the photon emission originating from primary and secondary electrons produced…
If dark matter inhabits an expanded "hidden sector", annihilations may proceed through sequential decays or multi-body final states. We map out the potential signals and current constraints on such a framework in indirect searches, using a model-independent setup based on multi-step hierarchical cascade decays. While remaining agnostic to the details of the hidden sector model, our framework captures the generic broadening of the spectrum of secondary particles (photons, neutrinos, e+e- and antiprotons) relative to the case of direct annihilation to Standard Model particles. We explore how ind…
In this paper we show that positron data from AMS seems 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 c…
We compute in detail the rate at which energy injected by dark matter annihilation heats and ionizes the photon-baryon plasma at z ~ 1000, and provide accurate fitting functions over the relevant redshift range for a broad array of annihilation channels and DM masses. The resulting perturbations to the ionization history can be constrained by measurements of the CMB temperature and polarization angular power spectra. We show that models which fit recently measured excesses in 10-1000 GeV electron and positron cosmic rays are already close to the 95% confidence limits from WMAP. The recently la…
Previous attempts at explaining the gamma-ray excess near the Galactic Centre have focussed on dark matter annihilation directly into Standard Model particles. This results in a preferred dark matter mass of 30-40 GeV (if the annihilation is into b quarks) or 10 GeV (if it is into leptons). Here we show that the gamma-ray excess is also consistent with heavier dark matter particles; in models of secluded dark matter, dark matter with mass up to 76 GeV provides a good fit to the data. This occurs if the dark matter first annihilates to an on-shell particle that subsequently decays to Standard M…
We update the constraint on the dark matter annihilation cross section by using the recent measurements of the CMB anisotropy by the Planck satellite. We fully calculate the cascade of dark matter annihilation products and their effects on ionization, heating and excitation of the hydrogen, hence do not rely on any assumption on the energy fractions that cause these effects.
Recently, ATLAS and CMS collaboration reported an excess in the diphoton events, which can be explained by a new resonance with mass around 750 GeV. In this work, we explored the possibility of identifying if the hypothetical new resonance is produced through gluon-gluon fusion or quark-antiquark annihilation, or tagging the beam. Three different observables for beam tagging, namely the rapidity and transverse momentum distribution of the diphoton, and one tagged bottom-jet cross section, are proposed. Combining the information gained from these observables, a clear distinction of the producti…
Sommerfeld-enhanced dark matter (DM) annihilation through $s$-wave has been widely considered as a consistent explanation for both the observed cosmic-ray (CR) positron excess and the DM thermal relic density. However, as the $s$-wave Sommerfeld-enhanced annihilation cross section increases monotonically with decreasing DM velocity, severe constraints appear from the data of gamma rays from dwarf spheroidal satellite galaxies (dSphs) and the cosmic microwave background (CMB), as the relevant typical DM velocities are even lower than that in the Galactic halo. In this work, we consider Sommerfe…
Recently data from PAMELA, ATIC, FERMI-LAT and HESS show that there are $e^{\pm}$ excesses in the cosmic ray energy spectrum. PAMELA observed excesses only in $e^+$, but not in anti-proton spectrum. ATIC, FERMI-LAT and HESS observed excesses in $e^++e^-$ spectrum, but the detailed shapes are different which requires future experimental observations to pin down the correct data set. Nevertheless a lot of efforts have been made to explain the observed $e^\pm$ excesses, and also why PAMELA only observed excesses in $e^+$ but not in anti-proton. In this brief review we discuss one of the most popu…
Observations by the Fermi-LAT telescope have uncovered a significant $γ$-ray excess toward the Milky Way Galactic Center. There has been no detection of a similar signal in the direction of the Milky Way dwarf spheroidal galaxies. Additionally, astronomical observations indicate that dwarf galaxies and other faint galaxies are less dense than predicted by the simplest cold dark matter models. We show that a self-interacting dark matter model with a particle mass of roughly 50 GeV annihilating to the mediator responsible for the strong self-interaction can simultaneously explain all three obser…
In this paper, we study rare decays $B_c\rightarrow D^{(*)}_{s,d}l\bar{l}$ within the Standard Model. The penguin, box, annihilation, color-favored cascade and color-suppressed cascade contributions are included. Based on our calculation, the annihilation and color-favored cascade diagrams play important roles in the differential branching fractions, forward-backward asymmetries, longitudinal polarizations of the final vector mesons and leptonic longitudinal polarization asymmetries. More importantly, color-favored cascade decays largely enhance the resonance cascade contributions. To avoid th…
This article is an exploration of gamma ray signals of annihilating Higgs-portal singlet scalar and vector dark matter. Gamma ray signals are considered in the context of contributions from annihilations of singlets in the galactic halo to the Isotropic Gamma Ray Background (IGRB), in the context of the Galactic center excess, and in the context of observations of dwarf spheroidal galaxies. We find that Higgs-portal singlets of both species with a mass of $~$65 GeV can explain the Galactic center excess with reasonable accuracy, but that this mass range is in tension with current direct detect…
We entertain the exotic possibility that dark matter (DM) decays or annihilations taking place in our galaxy may produce a flux of relativistic very weakly-coupled bosons, axions or dark photons. We show that there exist several upper bounds for this flux on Earth assuming generic minimal requirements for DM, such as a lifetime longer than the age of the Universe or an annihilation rate that leaves unaffected the background evolution during matter domination. These bounds do not depend on the identity or the couplings of the bosons. We then show that this new flux cannot be large enough to exp…
We present the effective $J$-factors for the Milky Way for scenarios in which dark matter annihilation is p-wave or d-wave suppressed. We find that the velocity suppression of dark matter annihilation can have a sizable effect on the morphology of a potential dark matter annihilation signal in the Galactic Center. The gamma-ray flux from the innermost region of the Galactic Center is in particular suppressed. We find that for dark matter density profiles with steep inner slopes, the morphology of the Inner Galaxy gamma-ray emission in p-wave models can be made similar to the morphology in stan…
Observations of the extragalactic radio background have uncovered a significant isotropic emission across multiple frequencies spanning from 22 MHz to 10 GHz. The intensity of this non-thermal emission component significantly exceeds the expected contribution from known astrophysical sources. Interestingly, models have indicated that the annihilation of dark matter particles may reproduce both the flux and spectrum of the excess. However, the lack of a measurable anisotropy in the residual emission remains challenging for both dark matter and standard astrophysical interpretations of the ARCAD…
We provide conservative bounds on the dark matter cross-section and lifetime from final state radiation produced by annihilation or decay into charged leptons, either directly or via an intermediate particle $ϕ$. Our analysis utilizes the experimental gamma-ray flux upper limits from four Milky Way dwarf satellites: HESS observations of Sagittarius and VERITAS observations of Draco, Ursa Minor, and Willman 1. Using 90% confidence level lower limits on the integrals over the dark matter distributions, we find that these constraints are largely unable to rule out dark matter annihilations or dec…
Dark matter (DM) annihilation in the galactic halo can be enhanced relative to that in the early Universe due to the Breit-Wigner enhancement, if the DM particles annihilate through a narrow resonance. Although the $s$-wave Breit-Wigner enhancement can provide a consistent explanation for both the observed cosmic-ray (CR) positron excess and the DM thermal relic density, it is severely constrained by the observations of gamma rays from dwarf spheroidal satellite galaxies (dSphs) and the cosmic microwave background (CMB), which have relatively lower allowed DM annihilation cross section and typ…
Recent results from experiments like PAMELA have pointed to excesses of e+e- in cosmic rays. If interpreted in terms of Dark Matter annihilations, they imply the existence of an abundant population of e+e- in the galactic halo at large. We consider the high energy gamma ray fluxes produced by Inverse Compton scattering of interstellar photons on such e+e-, and compare them with the available data from EGRET and some preliminary data from FERMI. We consider different observation regions of the sky and a range of DM masses, annihilation channels and DM profiles. We find that large portions of th…
It has recently been shown that dark-matter annihilation to bottom quarks provides a good fit to the galactic-center gamma-ray excess identified in the Fermi-LAT data. In the favored dark matter mass range $m\sim 30-40$ GeV, achieving the best-fit annihilation rate $σv \sim 5\times 10^{-26}$ cm$^{3}$ s$^{-1}$ with perturbative couplings requires a sub-TeV mediator particle that interacts with both dark matter and bottom quarks. In this paper, we consider the minimal viable scenarios in which a Standard Model singlet mediates s-channel interactions only between dark matter and bottom quarks, fo…
AMS-02 provided the unprecedented statistics in the measurement of the positron fraction from cosmic rays. That may offer a unique opportunity to distinguish the positron spectrum coming from various dark matter (DM) annihilation channels, if DM is the source of this positron excess. Therefore, we consider the scenario that the DM can annihilate into leptonic, quark, and massive gauge boson channels simultaneously with floating branching ratios to test this hypothesis. We also study the impacts from MAX, MED, MIN, and DC diffusion models as well as from isothermal, NFW, and Einasto DM density …
