1,720,986 research outputs found
Deciphering Gamma Rays from a Dwarf Galaxy
No full textAre gamma rays from a nearby dwarf galaxy a beacon of dark matter or a false alarm
Implications of a 21-cm signal for dark matter annihilation and decay
Get PDFMeasurements of the temperature of the baryons at the end of the cosmic dark ages can potentially set very precise constraints on energy injection from exotic sources, such as annihilation or decay of the dark matter. However, additional effects that lower the gas temperature can substantially weaken the expected constraints on exotic energy injection, whereas additional radiation backgrounds can conceal the effect of an increased gas temperature in measurements of the 21-cm hyperfine transition of neutral hydrogen. Motivated in part by recent claims of a detection of 21-cm absorption from z∼17 by the EDGES experiment, we derive the constraints on dark matter annihilation and decay that can be placed in the presence of extra radiation backgrounds or effects that modify the gas temperature, such as dark matter (DM)–baryon scattering and early baryon-photon decoupling. We find that if the EDGES observation is confirmed, then constraints on light DM decaying or annihilating to electrons will in most scenarios be stronger than existing state-of-the-art limits from the cosmic microwave background, potentially by several orders of magnitude. More generally, our results allow mapping any future measurement of the global 21-cm signal into constraints on dark matter annihilation and decay, within the broad range of scenarios we consider.United States. Department of Energy (Grant DE-SC00012567)United States. Department of Defense (Grant DE-SC0013999
Indirect dark matter signatures in the cosmic dark ages. I. Generalizing the bound on s-wave dark matter annihilation from Planck results
Get PDFRecent measurements of the cosmic microwave background (CMB) anisotropies by Planck provide a sensitive probe of dark matter annihilation during the cosmic dark ages, and specifically constrain the annihilation parameter f[subscript eff]⟨σv⟩/m[subscript χ]. Using new results (paper II) for the ionization produced by particles injected at arbitrary energies, we calculate and provide f[subscript eff] values for photons and e[superscript +]e[superscript -] pairs injected at keV-TeV energies; the f[subscript eff] value for any dark matter model can be obtained straightforwardly by weighting these results by the spectrum of annihilation products. This result allows the sensitive and robust constraints on dark matter annihilation presented by the Planck collaboration to be applied to arbitrary dark matter models with s-wave annihilation. We demonstrate the validity of this approach using principal component analysis. As an example, we integrate over the spectrum of annihilation products for a range of Standard Model final states to determine the CMB bounds on these models as a function of dark matter mass, and demonstrate that the new limits generically exclude models proposed to explain the observed high-energy rise in the cosmic ray positron fraction. We make our results publicly available at http://nebel.rc.fas.harvard.edu/epsilon.United States. Dept. of Energy (Grant Contract DE-SC00012567)United States. Dept. of Energy (Grant Contract DE-SC0013999
Indirect dark matter signatures in the cosmic dark ages. II. Ionization, heating, and photon production from arbitrary energy injections
Get PDFAny injection of electromagnetically interacting particles during the cosmic dark ages will lead to increased ionization, heating, production of Lyman-α photons and distortions to the energy spectrum of the cosmic microwave background, with potentially observable consequences. In this paper we describe numerical results for the low-energy electrons and photons produced by the cooling of particles injected at energies from keV to multi-TeV scales, at arbitrary injection redshifts (but focusing on the post-recombination epoch). We use these data, combined with existing calculations modeling the cooling of these low-energy particles, to estimate the resulting contributions to ionization, excitation and heating of the gas, and production of low-energy photons below the threshold for excitation and ionization. We compute corrected deposition-efficiency curves for annihilating dark matter, and demonstrate how to compute equivalent curves for arbitrary energy-injection histories. These calculations provide the necessary inputs for the limits on dark matter annihilation presented in the accompanying paper I, but also have potential applications in the context of dark matter decay or deexcitation, decay of other metastable species, or similar energy injections from new physics. We make our full results publicly available at http://nebel.rc.fas.harvard.edu/epsilon, to facilitate further independent studies. In particular, we provide the full low-energy electron and photon spectra, to allow matching onto more detailed codes that describe the cooling of such particles at low energies.United States. Dept. of Energy (Contract DE-SC00012567)United States. Dept. of Energy (Contract DE-SC0013999
Self-scattering for Dark Matter with an excited state
Get PDFSelf-interacting dark matter scenarios have recently attracted much attention, as a possible means to alleviate the tension between N-body simulations and observations of the dark matter distribution on galactic and sub-galactic scales. The presence of internal structure for the dark matter—for example, a nearly-degenerate state in the spectrum that could decay, or be collisionally excited or de-excited—has also been proposed as a possible means to address these discrepancies. Such internal structure can be a source of interesting signatures in direct and indirect dark matter searches, for example providing a novel explanation for the 3.5 keV line recently observed in galaxies and galaxy clusters. We analyze a simple model of dark matter self-scattering including a nearly-degenerate excited state, and develop an accurate analytic approximation for the elastic and inelastic s-wave cross sections, which is valid outside the perturbative regime provided the particle velocity is sufficiently low (this condition is also required for the s-wave to dominate over higher partial waves). We anticipate our results will be useful in incorporating inelastic self-scattering into N-body simulations, in order to study the quantitative impact of nearly-degenerate states in the dark matter spectrum on galactic structure and dynamics, and in computing the indirect signatures of multi-state dark matter.United States. Dept. of Energy (Cooperative Research Agreement Contract DE-FG02-05ER41360)Cameron and Hayden Lord Foundation (Fellowship)National Science Foundation (U.S.). Graduate Research FellowshipHertz Foundation (Fellowship
A latitude-dependent analysis of the leptonic hypothesis for the Fermi Bubbles
No full textThe Fermi Bubbles are giant Galactic structures observed in both gamma-rays and microwaves. Recent studies have found support for the hypothesis that the gamma-ray and microwave emission can both be understood as arising from a hard cosmic ray electron population within the volume of the Bubbles, via inverse Compton scattering and synchrotron radiation, respectively. The relative rates of these processes are set by the relative energy density of the interstellar radiation field and the magnetic field within the Bubbles; consequently, under the hypothesis of a common origin, the combination of the gamma-ray and microwave measurements can be used to estimate the magnetic field within the Bubbles. We revisit the consistency of this hypothesis on a latitude-by-latitude basis, using data from Fermi, WMAP and Planck; estimate the variation of the electron spectrum within the Bubbles; and infer bounds on the magnetic field within the Bubbles as a function of distance from the Galactic plane. We find that while the microwave and gamma-ray spectra are generally consistent with the leptonic hypothesis for few-microGauss magnetic fields, there appears to be a preference for spectral hardening in the microwaves at mid-latitudes (especially in the |b| ∼ 25°–35° range) that is not mirrored in the gamma-rays. This result may hint at a non-leptonic contribution to the gamma-ray spectra; however, the discrepancy can be reconciled in purely leptonic models if the cut-off energy for the electrons is lower in this latitude range and the spectrum below the cut-off is harder. Keywords: ISM: jets and outflows; gamma-rays: ISM; radio continuum: ISMUnited States. Department of Energy (Grant DE-SC00012567)United States. Department of Energy (Grant DE-SC0013999
Current dark matter annihilation constraints from CMB and low-redshift data
Get PDFUpdated constraints on the dark matter cross section and mass are presented combining cosmic microwave background (CMB) power spectrum measurements from Planck, WMAP9, ACT, and SPT as well as several low-redshift data sets (BAO, HST, and supernovae). For the CMB data sets, we combine WMAP9 temperature and polarization data for l ≤ 431 with Planck temperature data for 432 ≤ l ≤ 2500, ACT and SPT data for l > 2500, and Planck CMB four-point lensing measurements. We allow for redshift-dependent energy deposition from dark matter annihilation by using a “universal" energy absorption curve. We also include an updated treatment of the excitation, heating, and ionization energy fractions and provide an updated deposition efficiency factors (f[subscript eff]) for 41 different dark matter models. Assuming perfect energy deposition (f[subscript eff] = 1) and a thermal cross section, dark matter masses below 26 GeV are excluded at the 2σ level. Assuming a more generic efficiency of f[subscript eff] = 0.2, thermal dark matter masses below 5 GeV are disfavored at the 2σ level. These limits are a factor of ∼2 improvement over those from WMAP9 data alone. These current constraints probe, but do not exclude, dark matter as an explanation for reported anomalous indirect detection observations from AMS-02/PAMELA and the Fermi gamma-ray inner-Galaxy data. They also probe relevant models that would explain anomalous direct detection events from CDMS, CRESST, CoGeNT, and DAMA, as originating from a generic thermal weakly interacting massive particle. Projected constraints from the full Planck release should improve the current limits by another factor of ∼2 but will not definitely probe these signals. The proposed CMB Stage IV experiment will more decisively explore the relevant regions and improve upon the Planck constraints by another factor of ∼2.Stony Brook University-Brookhaven National Laboratory (Research Initiatives Seed Grant 37298, Project 1111593)United States. Dept. of Energy (Cooperative Research Agreement Contract DE-FG02-05ER41360
Self-consistent calculation of the Sommerfeld enhancement
No full textA calculation of the Sommerfeld enhancement is presented and applied to the problem of s-wave non-relativistic dark matter annihilation. The difference from previous computations in the literature is that the effect of the underlying short-range scattering process is consistently included together with the long-range force in the effective QM Schrödinger problem. Our procedure satisfies partial-wave unitarity where previous calculations fail. We provide analytic results for some potentials of phenomenological relevance.United States. Department of Energy (grant contract number DE-SC00012567)United States. Department of Energy (grant contract number DE−SC0013999)Japan Society for the Promotion of Science (JSPS Research Fellowships for Young Scientists
Heavy Dark Matter Annihilation from Effective Field Theory
Get PDFWe formulate an effective field theory description for SU(2)[subscript L] triplet fermionic dark matter by combining nonrelativistic dark matter with gauge bosons in the soft-collinear effective theory. For a given dark matter mass, the annihilation cross section to line photons is obtained with 5% precision by simultaneously including Sommerfeld enhancement and the resummation of electroweak Sudakov logarithms at next-to-leading logarithmic order. Using these results, we present more accurate and precise predictions for the gamma-ray line signal from annihilation, updating both existing constraints and the reach of future experiments.United States. Dept. of Energy (Grant DE-SC00012567)United States. Dept. of Energy (Grant DE-SC0011090)Simons Foundation (Investigator Grant 327942
Complementarity for dark sector bound states
No full textWe explore the possibility that bound states involving dark matter particles could be detected by resonance searches at the LHC and the generic implications of such scenarios for indirect and direct detection. We demonstrate that resonance searches are complementary to monojet searches and can probe dark matter masses above 1 TeV with current LHC data. We argue that this parameter regime, in which the bound-state resonance channel is the most sensitive probe of the dark sector, arises most naturally in the context of nontrivial dark sectors with large couplings, nearly degenerate dark matter–like states, and multiple force carriers. If dark sector bound states are present and can be detected at the LHC, annihilation of dark matter particles in our galactic halo may occur either with a minimal Sommerfeld enhancement that may be appreciable or through radiative bound-state formation, leading to large signals in indirect searches. We calculate these complementary constraints, which favor either models in which the bound state–forming dark matter constitutes a small fraction of the total density or models in which the late-time annihilation is suppressed at low velocities or late times. We present concrete examples of models that satisfy all these constraints and in which the LHC resonance search is the most sensitive probe of the dark sector.United States. Department of Energy. High Energy Physics Division (Grant DE-SC00012567)United States. Department of Energy (Grant DE-SC0013999)United States. Department of Energy (Grant DE-SC00015476)MIT Research Support Committe
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