Anisotropies of the cosmic microwave background (CMB) have proven to be a very powerful tool to constrain dark matter annihilation at the epoch of recombination. However, CMB constraints are currently derived using a number of reasonable but yet un-tested assumptions that could potentially lead to a misestimation of the true bounds. In this paper we examine the potential impact of these systematic effects. In particular, we separately study the propagation of the secondary particles produced by annihilation in two energy regimes; first following the shower from the initial particle energy to the keV scale, and then tracking the resulting secondary particles from this scale to the absorption of their energy as heat, ionization, or excitation of the medium. We improve both the high and low energy parts of the calculation, in particular finding that our more accurate treatment of losses to sub-10.2 eV photons produced by scattering of high-energy electrons weakens the constraints on particular DM annihilation models by up to a factor of two. On the other hand, we find that the uncertainties we examine for the low energy propagation do not significantly affect the results for current and upcoming CMB data. We include the evaluation of the precise amount of excitation energy, in the form of Lyman-alpha photons, produced by the propagation of the shower, and examine the effects of varying the Helium fraction and Helium ionization fraction. In the recent literature, simple approximations for the fraction of energy absorbed in different channels have often been used to derive CMB constraints: we assess the impact of using accurate versus approximate energy fractions. Finally we check that the choice of recombination code (between RECFAST v1.5 and COSMOREC), to calculate the evolution of the free electron fraction in the presence of dark matter annihilation, introduces negligible differences.
We study the effects of dark matter annihilation during and after the cosmic recombination epoch on the cosmic microwave background anisotropy, taking into account the detailed energy deposition of the annihilation products. It is found that a fairly stringent constraint on the annihilation cross section is imposed for TeV scale dark matter masses from WMAP observations.
I summarize the recent advances in determining the effects of self-annihilating WIMP dark matter on the modification of the recombination history, at times earlier than the formation of astrophysical objects. Depending on mass and self-annihilation cross section, WIMP DM can reproduce sizable amounts of the total free electron abundance at z > 6; as known, this affects the CMB temperature and polarization correlation spectra, and can be used to place stringent bounds in the particle mass vs cross-section plane. WMAP5 data already strongly disfavor the region capable to explain the recent cosmi…
To reveal natures of the dark matter (DM) particles, a gamma-ray signal produced in annihilation processes of DM into the standard model particles has been one of the major probes. The cross-correlation between highly DM dominated structures, such as local dwarf galaxies, and observed photons in the direction of the structures, has been explored and provided stringent constraints on the annihilation rate. In our previous work, we have shown that it is sufficient to know the distance distribution of the galaxy sample and individual distance measurement is not required for constraining the annih…
Constraining Primordial Black Holes via p-wave annihilation in light of CMB Spectral Distortion and 21-cm global signal
National Institute of Technology, Meghalaya（梅加拉亚国立技术学院）；Hangzhou Institute for Advanced Study, UCAS（杭州高等研究院）；University of Chinese Academy of Sciences（中国科学院大学）
In a large class of models we show that the light scalar field responsible for the Sommerfeld enhancement in the annihilation of dark matter leads to observable direct detection rates, due to its mixing with the standard model Higgs. As a result the large annihilation cross-section of dark matter at present epoch, required to explain the observed cosmic ray anomalies, can be strongly constrained by direct searches. In particular Sommerfeld boost factors of order of a few hundred are already out of the CDMS-II upper bound at 90% confidence level for reasonable values of the model parameters.
Most proposed dark matter candidates are stable and are produced thermally in the early Universe. However, there is also the possibility of unstable (but long-lived) dark matter, produced thermally or otherwise. We propose a strategy to distinguish between dark matter annihilation and/or decay in the case that a clear signal is detected in gamma-ray observations of Milky Way dwarf spheroidal galaxies with gamma-ray experiments. The sole measurement of the energy spectrum of an indirect signal would render the discrimination between these cases impossible. We show that by examining the dependen…
In the cold dark matter scenario, galactic dark matter halos are populated with a large number of smaller subhalos. Previous work has shown that dark matter annihilations in subhalos can generate a distinctive, non-Poisson signal in the gamma-ray photon counts probability distribution function (PDF). Here we show that the gamma-ray PDF also carries information about the velocity dependence of the dark matter annihilation cross section. After calculating the PDF assuming $s$-wave and Sommerfeld-enhanced annihilation, we perform a mock data analysis to illustrate how current and future observati…
Cold dark matter models predict the existence of a large number of substructures within dark matter halos. If the cold dark matter consists of weakly interacting massive particles, their annihilation within these substructures could lead to diffuse GeV emission that would dominate over the annihilation signal of the host halo. In this work we search for GeV emission from three nearby galaxy clusters: Coma, Virgo and Fornax. We first remove known extragalactic and galactic diffuse gamma-ray backgrounds and point sources from the Fermi 2-year catalog and find a significant residual diffuse emiss…
The self-annihilation of dark matter particles with mass in the MeV range can produce gamma rays via prompt or secondary radiation. The annihilation rate for such light dark matter particles is however tightly constrained by cosmic microwave background (CMB) data. Here we explore the possibility of discovering MeV dark matter annihilation with future MeV gamma-ray telescopes taking into account the latest and future CMB constraints. We study the optimal energy window as a function of the dominant annihilation final state. We consider both the (conservative) case of the dwarf spheroidal galaxy …
Although most proposed dark matter candidates are stable, in order for dark matter to be present today, the only requirement is that its lifetime is longer than the age of the Universe, t_U ~ 4 10^17 s. Moreover, the dark matter particle could be produced via non-thermal processes and have a larger annihilation cross section from the canonical value for thermal dark matter, <sigma v> ~ 3 10^{-26} cm3/s. We propose a strategy to distinguish between dark matter annihilation and/or decay in the case that a clear signal is detected in future gamma-ray observations of Milky Way dwarf galaxies with …
We use the latest cosmic microwave background (CMB) observations to provide updated constraints on the dark matter lifetime as well as on p-wave suppressed annihilation cross sections in the 1 MeV to 1 TeV mass range. In contrast to scenarios with an s-wave dominated annihilation cross section, which mainly affect the CMB close to the last scattering surface, signatures associated with these scenarios essentially appear at low redshifts ($z \lesssim 50$) when structure began to form, and thus manifest at lower multipoles in the CMB power spectrum. We use data from Planck, WMAP9, SPT and ACT, a…
Searches for dark matter annihilation signals have been carried out in a number of target regions such as the Galactic Center and Milky Way dwarf spheroidal galaxies (dSphs), among a few others. Here we propose low surface brightness galaxies (LSBGs) asnovel targets for the indirect detection of dark matter emission. In particular, LSBGs are known to have very large dark matter contents and be less contaminated by extragalactic gamma-ray sources (e.g., blazars) compared to star forming galaxies. We report on an analysis that uses eight LSBGs (detected by Subaru Hyper Suprime-Cam survey data) w…
We present the first search for signatures of brane-world extra-dimensional dark matter (DM) in the very-high-energy gamma-ray band by scrutinizing observations of the dwarf spheroidal galaxy Segue 1 with the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope system. Branons are new degrees of freedom that appear within flexible brane-world models: they are weakly interacting massive particles and natural DM candidates. The ground-based gamma-ray telescopes MAGIC could indirectly detect branon DM in the multi-TeV mass range by observing secondary products of DM annihilation into Stand…
The presence of dark matter in the halo of our galaxy could be revealed through indirect detection of annihilation products. Dark matter annihilation is one of the possible interpretations of the recent measured excesses in positron and electron fluxes, once boost factors of the order of 10^3 or more are taken into account. Such boost factors are actually achievable through the velocity-dependent Sommerfeld enhancement of the annihilation cross-section. Here we study the expected gamma-ray flux from two local dwarf galaxies for which air Cerenkov measurements are available, namely Draco and Sa…
The nature of the Isotropic $γ$-ray Background (IGRB) measured by the Large Area Telescope (LAT) on the Fermi $γ$-ray space Telescope ({\it Fermi}) remains partially unexplained. Non-negligible contributions may originate from extragalactic populations of unresolved sources such as blazars, star-forming galaxies or galactic milli-second pulsars. A recent prediction of the diffuse $γ$-ray emission from Active Galactic Nuclei (AGN) with a large viewing angle with respect to the line-of-sight (l.o.s.) has demonstrated that this faint but numerous population is also expected to contribute signific…
The cosmic microwave background (CMB) observation by the Planck satellite precisely determines primordial curvature fluctuations on larger scales than $\mathcal O(1)\,\mathrm{Mpc}$, while the small-scale curvature fluctuation is still less constrained. The constraint on small-scale fluctuations is highly improved if we assume the standard thermal relic dark matter scenario. When small-scale fluctuations are large enough, dense regions collapse to form small halos even in a redshift $z\gtrsim10^3$, which is called ultracompact minihalos. These minihalos enhance the annihilation of the dark matt…
We investigate the possibilities of constraining the light gravitino mass m_{3/2} from future cosmic microwave background (CMB) surveys. A model with light gravitino with the mass m_{3/2}<O(10) eV is of great interest since it is free from the cosmological gravitino problem and, in addition, can be compatible with many baryogenesis/leptogenesis scenarios such as the thermal leptogenesis. We show that the lensing of CMB anisotropies can be a good probe for m_{3/2} and obtain an expected constraint on m_{3/2} from precise measurements of lensing potential in the future CMB surveys, such as the P…
It is commonly assumed that the stochastic background of gravitational waves on cosmological scales follows an almost scale-independent power spectrum, as generically predicted by the inflationary paradigm. However, it is not inconceivable that the spectrum could have strongly scale-dependent features, generated, e.g., via transient dynamics of spectator axion-gauge fields during inflation. Using the temperature and polarisation maps from the \textit{Planck} and BICEP/Keck datasets, we search for such features, taking the example of a log-normal bump in the primordial tensor spectrum at CMB sc…
Unveiling the nature of cosmic dark matter (DM) is an urgent issue in cosmology. Here we make use of a strategy based on the search for the imprints left on the cosmic microwave background temperature and polarization spectra by the energy deposition due to annihilations of the most promising dark matter candidate, a stable WIMP of mass 1-20 GeV. A major improvement with respect to previous similar studies is a detailed treatment of the annihilation cascade and its energy deposition in the cosmic gas. This is vital as this quantity is degenerate with the annihilation cross-section <σv>. The st…
We optimise the parameters of the Population Monte Carlo algorithm using numerical simulations. The optimisation is based on an efficiency statistic related to the number of samples evaluated prior to convergence, and is applied to a D-dimensional Gaussian distribution to derive optimal scaling laws for the algorithm parameters. More complex distributions such as the banana and bimodal distributions are also studied. We apply these results to a cosmological parameter estimation problem that uses CMB anisotropy data from the WMAP nine-year release to constrain a six parameter adiabatic model an…
Analyses have found a "haze" of anomalous microwave emission surrounding the Galactic Center in the WMAP sky maps. A recent study using Fermi data detected a similar haze in the gamma-ray. Several studies have modeled these hazes as radiation from the leptonic byproducts of dark matter annihilations, and arguably no convincing astrophysical alternative has been suggested. We discuss the characteristics of astrophysical cosmic ray sources that could potentially explain this microwave and gamma-ray emission. The most promising astrophysical scenarios involve cosmic ray sources that are clustered…
We examine how the properties of dark matter, parameterised by an equation of state parameter $w$ and two perturbative Generalised Dark Matter (GDM) parameters $c^2_s$ (the sound speed) and $c^2_\text{vis}$ (the viscosity), are constrained by existing cosmological data, particularly the Planck 2015 data release. We find that the GDM parameters are consistent with zero, and are strongly constrained, showing no evidence for extending the dark matter model beyond the Cold Dark Matter (CDM) paradigm. The dark matter equation of state is constrained to be within $-0.000896<w<0.00238$ at the $99.7\%…
Photons produced in the annihilations of dark matter particles can be detected by gamma-ray telescopes; this technique of indirect detection serves as a cornerstone of the upcoming assault on the dark matter paradigm. The main obstacle to the extraction of information about dark matter from the annihilation photons is the presence of large and uncertain gamma-ray backgrounds. We present a new technique for using gamma-ray data to constrain the properties of dark matter that makes minimal assumptions about the dark matter and the backgrounds. The technique relies on two properties of the expect…
We consider the imprint of superradiant instabilities of nonevaporating primordial black holes (PBHs) on the spectrum of the cosmic microwave background (CMB). In the radiation dominated era, PBHs are surrounded by a roughly homogeneous cosmic plasma which endows photons with an effective mass through the plasma frequency. In this setting, spinning PBHs are unstable to a spontaneous spindown through the well-known "black-hole bomb" mechanism. At linear level, the photon density is trapped by the effective photon mass and grows exponentially in time due to superradiance. As the plasma density d…
We investigate constraints on the time variation of the fine structure constant between the recombination epoch and the present epoch, Δα/α\equiv (α_{rec} - α_{now})/α_{now}, from cosmic microwave background (CMB) taking into account simultaneous variation of other physical constants, namely the electron mass m_{e} and the proton mass m_{p}. In other words, we consider the variation of Yukawa coupling and the QCD scale Λ_{QCD} in addition to the electromagnetic coupling. We clarify which parameters can be determined from CMB temperature anisotropy in terms of singular value decomposition. Assu…
We consider the propagation and energy losses of protons and anti-protons produced by dark matter annihilation at redshifts 100<z<~2000. In the case of dark matter annihilations into quarks, gluons and weak gauge bosons, protons and anti-protons carry about 20% of the energy injected into e^\pm and γ's, but their interactions are normally neglected when deriving cosmic microwave background bounds from altered recombination histories. Here, we follow numerically the energy-loss history of typical protons/antiprotons in the cosmological medium. We show that about half of their energy is channele…
We present the first branon dark matter (DM) search in the very high-energy gamma-ray band with observations of the dwarf spheroidal galaxy Segue~1 carried out by the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope system. Branons are new degrees of freedom that appear in flexible brane-world models corresponding to brane fluctuations. They behave as weakly interacting massive particles, which are natural DM candidates. In the absence of a gamma-ray signal in the Segue~1 data, we place constraints on the branon DM parameter space by using a binned likelihood analysis. Our most cons…
In the past decade, the properties of annihilating dark matter models were examined by various kinds of data, including the data of gamma rays, radio waves, X-ray, positrons, electrons, antiprotons and neutrinos. In particular, most of the studies focus on the data of our Galaxy, nearby galaxies (e.g. M31 galaxy) or nearby galaxy clusters (e.g. Fornax cluster). In this article, we examine the archival radio continuum spectral data of a relatively high-redshift galaxy cluster (A697 cluster) to constrain the properties of annihilating dark matter. We find that leptophilic annihilation channels (…
The high positron production rate required to explain the flux of 511 keV gamma rays from the galactic center has inspired many models in which dark matter creates positrons. These models include the annihilation of light dark matter and scattering of dark matter with excited states (exciting dark matter). We show that existing cosmic microwave background data robustly constrains such models when the annihilation or scattering cross section is not velocity suppressed depending on the model of the galactic dark matter halo. Upcoming data from the Planck mission can exclude the fiducial Via Lact…
We constrain the deviation of adiabatic evolution of the Universe using the data on the Cosmic Microwave Background (CMB) temperature anisotropies measured by the {\it Planck} satellite and a sample of 481 X-ray selected clusters with spectroscopically measured redshifts. To avoid antenna beam effects, we bring all the maps to the same resolution. We use a CMB template to subtract the cosmological signal while preserving the Thermal Sunyaev-Zeldovich (TSZ) anisotropies; next, we remove galactic foreground emissions around each cluster and we mask out all known point sources. If the CMB black-b…
We derive cosmological constraints on the annihilation cross section of dark matter with velocity-dependent structure, motivated by annihilating dark matter models through Sommerfeld or Breit-Wigner enhancement mechanisms. In models with annihilation cross section increasing with decreasing dark matter velocity, big-bang nucleosynthesis and cosmic microwave background give stringent constraints.
We forecast the constraints on the parameters of neutrino physics with the constructions of Cosmic Microwave Background (CMB) temperature, E-mode polarization and lensing spectra for the ground-based Ali Cosmic Microwave Background Polarization Telescope (AliCPT). To implement the forecast calculations, we perform numerical simulations which show that AliCPT would yield the result $σ(N_{\mathrm{eff}})=0.42$ and $σ(M_ν)=0.18$ for the first year observation. Moreover, we investigate how the instrumental parameters, such as noise level, full width at half maxima (FWHM), and sky coverage can affec…
The precision measurements of the cosmic microwave background power spectrum put a strong constraint on the dark matter annihilation cross section since the electromagnetic energy injection by the dark matter annihilation affects the ionization history of the universe. In this paper, we update our previous simulation code for calculating the ionization history with the effect of dark matter annihilation by including Helium interactions and improving the precision of calculations. We give an updated constraint on the annihilation cross section and mass of dark matter using the modified RECFAST …
Detecting the dark matter annihilation signal from Galactic substructure, or subhalos, is an important challenge for high-energy gamma-ray experiments. In this paper we discuss detection prospects by combining two different aspects of the gamma-ray signal: the angular distribution and the photon counts probability distribution function (PDF). The true PDF from subhalos has been shown recently (by Lee et al.) to deviate from Poisson; we extend this analysis and derive the signal PDF from a detailed Lambda-CDM-based model for the properties of subhalos. We combine our PDF with a model for Galact…
Gamma rays and microwave observations of the Galactic Center and surrounding areas indicate the presence of anomalous emission, whose origin remains ambiguous. The possibility of dark matter (DM) annihilation explaining both signals through prompt emission at gamma-rays and secondary emission at microwave frequencies from interactions of high-energy electrons produced in annihilation with the Galactic magnetic fields has attracted much interest in recent years. We investigate the DM interpretation of the Galactic Center gamma-ray excess by searching for the associated synchrotron in the WMAP-P…
It was proposed that the massive compact halo objects (MCHOs) would be produced during an earlier epoch of cosmology if the density perturbations are between $3 \times 10^{-4}$ and 0.3. Then these objects can accrete dark matter particles onto them due to their high density. If the dark matter is in the form of the weakly interacting massive particles, the MCHOs can have a significant effect on the evolution of cosmology due to the dark matter annihilation within them. Using the WMAP-7 years data, we investigated the constraints on the current abundance of MCHOs ($f_{MCHOs}$) formed during the…
The injection of secondary particles produced by Dark Matter (DM) annihilation at redshift 100<z<1000 affects the process of recombination, leaving an imprint on Cosmic Microwave Background (CMB) anisotropies. Here we provide a new assessment of the constraints set by CMB data on the mass and self-annihilation cross-section of DM particles. Our new analysis includes the most recent WMAP (7-year) and ACT data, as well as an improved treatment of the time-dependent coupling between the DM annihilation energy with the thermal gas. We show in particular that the improved measurement of the polariz…
The EDGES Collaboration has recently reported the detection of a stronger-than-expected absorption feature in the global 21-cm spectrum, centered at a frequency corresponding to a redshift of z ~ 17. This observation has been interpreted as evidence that the gas was cooled during this era as a result of scattering with dark matter. In this study, we explore this possibility, applying constraints from the cosmic microwave background, light element abundances, Supernova 1987A, and a variety of laboratory experiments. After taking these constraints into account, we find that the vast majority of …
We reanalyse the anisotropic galaxy clustering measurement from the Baryon Oscillation Spectroscopic Survey (BOSS), demonstrating that using the full shape information provides cosmological constraints that are comparable to other low-redshift probes. We find $Ω_\mathrm{m} = 0.317^{+0.015}_{-0.019}$, $σ_8 = 0.710\pm 0.049$, and $h = 0.704\pm 0.024$ for flat $Λ$CDM cosmologies using uninformative priors on $Ω_\mathrm{c}h^2$, $100θ_\mathrm{MC}$, $\ln 10^{10} A_{s}$, and $n_{s}$, and a prior on $Ω_\mathrm{b}h^2$ that is much wider than current constraints. We quantify the agreement between the Pl…
We consider a dark sector consisting of dark matter that is a Dirac fermion and a scalar mediator. This model has been extensively studied in the past. If the scalar couples to the dark matter in a parity conserving manner then dark matter annihilation to two mediators is dominated by the P-wave channel and hence is suppressed at very low momentum. The indirect detection constraint from the anisotropy of the Cosmic Microwave Background is usually thought to be absent in the model because of this suppression. In this letter we show that dark matter annihilation to bound states occurs through th…
Anomalous microwave emission (AME) is a category of Galactic signals that cannot be explained by synchrotron radiation, thermal dust emission, or optically thin free-free radiation. Spinning dust is one variety of AME that could be partially polarized and therefore relevant for ongoing and future cosmic microwave background polarization studies. The Planck satellite mission identified candidate AME regions in approximately $1^\circ$ patches that were found to have spectra generally consistent with spinning dust grain models. The spectra for one of these regions, G107.2+5.2, was also consistent…
Observational limits on $y$- and $μ$-type distortions can constrain properties of magnetic fields in the early universe. For a Gaussian, random, and non-helical field, $μ$ and $y$ are calculated a function of the present-day strength of the field, $B_0$, smoothed over a certain Gaussian width, $k_c^{-1}$, and spectral index, $n_B$, defined by $P_B(k)\propto k^{n_B}$. For $n_B=-2.9$ and $k_c^{-1}=1 {\rm Mpc}$, the COBE/FIRAS limit on $μ$ yields $B_0<40$ nG, whereas the projected PIXIE limit on $μ$ would yield $B_0<0.8$ nG. For non-scale-invariant spectra, constraints can be stronger. For $B_0=1…
We consider the dark matter (DM) scenarios consisting of the mixture of WIMPs and PBHs and study how much fraction of the total DM can be PBHs. In such scenarios, PBHs can accrete the WIMPs and consequently enhance the heating and ionization in the intergalactic medium due to WIMP annihilations. We demonstrate that the CMB data can give the stringent bounds on the allowed PBH fraction which are comparable or even tighter than those from the gamma ray data depending on the DM masses. For instance, the MCMC likelihood analysis using the Planck CMB data leads to the bound on PBH DM fraction with …
We present constraints on decaying and annihilating dark matter (DM) in the 4 keV to 10 GeV mass range, using published results from the satellites HEAO-1, INTEGRAL, COMPTEL, EGRET, and the Fermi Gamma-ray Space Telescope. We derive analytic expressions for the gamma-ray spectra from various DM decay modes, and find lifetime constraints in the range 10^24-10^28 sec, depending on the DM mass and decay mode. We map these constraints onto the parameter space for a variety of models, including a hidden photino that is part of a kinetically mixed hidden sector, a gravitino with R-parity violating d…
Following Kamionkowski (2008), a quadratic estimator of the rotation of the plane of polarization of the CMB is constructed. This statistic can estimate a spatially varying rotation angle. We use this estimator to quantify the prospects of detecting such a rotation field with forthcoming experiments. For PLANCK and CMBPol we find that the estimator containing the product of the E and B components of the polarization field is the most sensitive. The variance of this EB estimator, N(L) is roughly independent of the multipole L, and is only weakly dependent on the instrumental beam. For FWHM of t…
We study the growth of cosmic structure under the assumption that dark matter self-annihilates with an averaged cross section times relative velocity that grows with the scale factor, an increase known as Sommerfeld-enhancement. Such an evolution is expected in models in which a light force carrier in the dark sector enhances the annihilation cross section of dark matter particles, and has been invoked, for instance, to explain anomalies in cosmic ray spectra reported in the past. In order to make our results as general as possible, we assume that dark matter annihilates into a relativistic sp…
