Annihilation Cross Section Research Articles

Sommerfeld enhancement at NLO and the dark matter unitarity bound

We reexamine the consequences of perturbative unitarity on dark matter freeze-out when both Sommerfeld enhancement and bound state formation affect dark matter annihilations. At leading order the annihilation cross section is infrared dominated and the connection between the unitarity bound and the upper bound on the dark matter mass depends only on how the different partial waves are populated. We compute how this picture is modified at next-to-leading order with the goal of assigning a reliable theory uncertainty to the freeze-out predictions. We explicitly compute next-to-leading order corrections in a simple model with Abelian gauge interactions and provide an estimate of the theoretical uncertainty for the thermal masses of heavy electroweak n-plets. Along the way, we clarify the regularization and matching procedure necessary to deal with singular potentials in quantum mechanics with a calculable, relativistic UV completion. Published by the American Physical Society 2024

Searching accretion-enhanced dark matter annihilation signals in the Galactic Centre

This study reanalyzes the detection prospects of dark matter (DM) annihilation signals in the Galactic Center, focusing on velocity-dependent dynamics within a spike density near the supermassive black hole (Sgr A⋆). We investigate three annihilation processes — p-wave, resonance, and forbidden annihilation — under semi-relativistic velocities, leveraging gamma-ray data from Fermi and DAMPE telescopes. Our analysis integrates a fermionic DM model with an electroweak axion-like particle (ALP) portal, exploring annihilation into two or four photons. Employing a comprehensive six-dimensional integration, we precisely calculate DM-induced gamma-ray fluxes near Sgr A⋆, incorporating velocity and positional dependencies in the annihilation cross-section and photon yield spectra. Our findings highlight scenarios of resonance and forbidden annihilation, where the larger ALP-DM-DM coupling constant Caχχ can affect spike density, potentially yielding detectable gamma-ray line spectra within Fermi and DAMPE energy resolution. We set upper limits for Caχχ across these scenarios, offering insights into the detectability and spectral characteristics of DM annihilation signals from the Galactic Center.

Indirect Detection for Higgs Portal Majorana Fermionic Dark Matter

Abstract We study the $\gamma$-ray signal emitted from dark matter (DM) pair annihilation in the Higgs portal Majorana fermion DM model. In the model, a Majorana fermion DM $\chi$ couples with the Standard Model (SM) Higgs field $H$ through a higher-dimensional term $-{\cal L}\supset H^\dagger H \bar{\chi }\chi /\Lambda$, where $\Lambda$ is a cutoff scale [1]. The pair annihilation of $\chi$ through the above term produces the Higgs boson and the longitudinal modes of $W,Z$ gauge bosons. The Milky Way dwarf spheroidal satellite galaxies (dSphs) are used as the most promising targets to search for the $\gamma$-ray signal of the model, due to high DM density and lack of astrophysical backgrounds. The Fermi Large Area Telescope (Fermi-LAT) is used for the search, for its high sensitivity [2]. In this work, we use 14-year Fermi-LAT data from 16 dSphs, to constrain the DM pair annihilation cross section for the DM mass range from 125 GeV to 100 TeV.

Search for dark matter annihilation to gamma-rays from SPT-SZ selected galaxy clusters

We search for dark matter annihilation from galaxy clusters in the energy range from 1–300 GeV using nearly 16 years of Fermi-LAT data. For this purpose, we use 350 galaxy clusters selected fromthe 2500 deg2 SPT-SZ survey. We model the dark matter distribution using the NFW profile for the main halo along with the Einasto profile for the substructure. The largest signal is seen for the cluster SPT-CL J2021-5257 with a significance of around 3σ. The best-fit dark matter mass and annihilation cross-section for this cluster are equal to (60.0 ± 11.8) GeV and ⟨σv⟩ = (6.0 ± 0.6) × 10-25 cm3 s-1 for the b̅ b annihilation channel. However, this central estimate is in conflict with the limits on annihilation cross-section from dwarf spheroidal galaxies, and hence cannot be attributed to dark matter annihilation. Three other clusters show significance between 2-2.5σ, whereas all the remaining clusters show null results. The most stringent 95% c.l. upper limit for the WIMP annihilation cross-section among all the clusters is from SPT-CL J0455-4159, viz. ⟨σv⟩ = 6.44 × 10-26 cm3 s-1 for m χ = 10 GeV and b b̅ annihilation channel.

Significant impact of Galactic dark matter particles on annihilation signals from Sagittarius analogues

We examine the gamma-ray signal from dark matter (DM) annihilation from analogues of the Sagittarius (Sgr) dwarf spheroidal galaxy in the Auriga cosmological simulations. For velocity-dependent annihilation cross sections, we compute emissions from simulated Sgr subhalos and from the Milky Way (MW) foreground. In addition to the annihilation signals from DM particles bound to Sgr, we consider for the first time the annihilation of DM particles bound to the MW that overlap spatially with Sgr. For p-wave models this contribution can enhance the signal by over an order of magnitude, while for d-wave models the enhancement can be over three orders of magnitude. For Sommerfeld and s-wave models, the corresponding emission does not significantly change. For the Sommerfeld model, the Sgr source can be visible above the MW foreground emission, while for s, p and d-wave models, the signal towards Sgr is most likely dominated by foreground MW emission. We interpret our results within the context of the observed gamma-ray emission from Sgr. We find that, given the background emission estimated from this region, the templates from simulations likely have spatial morphology that is too extended to explain the point-like emission that is observed.

Prospects for γ-ray observations of the Perseus galaxy cluster with the Cherenkov Telescope Array

Galaxy clusters are expected to be both dark matter (DM) reservoirs and storage rooms for the cosmic-ray protons (CRp) that accumulate along the cluster's formation history. Accordingly, they are excellent targets to search for signals of DM annihilation and decay at γ-ray energies and are predicted to be sources of large-scale γ-ray emission due to hadronic interactions in the intracluster medium (ICM).In this paper, we estimate the sensitivity of the Cherenkov Telescope Array (CTA) to detect diffuse γ-ray emission from the Perseus galaxy cluster.We first perform a detailed spatial and spectral modelling of the expected signal for both the DM and the CRp components. For each case, we compute the expected CTA sensitivity accounting for the CTA instrument response functions. The CTA observing strategy of the Perseus cluster is also discussed.In the absence of a diffuse signal (non-detection), CTA should constrain the CRp to thermal energy ratio X 500 within the characteristic radius R 500 down to about X 500 < 3 × 10-3, for a spatial CRp distribution that follows the thermal gas and a CRp spectral index αCRp = 2.3. Under the optimistic assumption of a pure hadronic origin of the Perseus radio mini-halo and depending on the assumed magnetic field profile, CTA should measure αCRp down to about ΔαCRp ≃ 0.1 and the CRp spatial distribution with 10% precision, respectively. Regarding DM, CTA should improve the current ground-based γ-ray DM limits from clusters observations on the velocity-averaged annihilation cross-section by a factor of up to ∼ 5, depending on the modelling of DM halo substructure. In the case of decay of DM particles, CTA will explore a new region of the parameter space, reaching models with τ χ > 1027 s for DM masses above 1 TeV.These constraints will provide unprecedented sensitivity to the physics of both CRp acceleration and transport at cluster scale and to TeV DM particle models, especially in the decay scenario.

Gamma-ray signal from ZN≥3 dark matter-companion models

In Ref. [10], we proposed to replace the final dark matter (DM) particle in the semi-annihilation mode DM+DM→antiDM+Higgs boson with its ZN≥3 companion, thus reducing DM number density without DM-nucleon scattering. In this work, we study the indirect detection signals from DM annihilation, the Higgs boson pair with one of them from the companion decay being on- or off- shell, depending on the DM-companion mass splitting. We generate the photon spectrum by using PYTHIA8 and study the properties of the spectrum, to find that the hard part of the spectrum in our model is mainly shaped by the direct Higgs boson and thus does not differ much from that of the conventional semi-annihilation mode. Using the Fermi-LAT data of dwarf spheroidal galaxies, we derive the current limit of the DM annihilation cross section for DM+DM→companion⁎+Higgs boson, and for the relatively light DM, it reaches the typical thermal cross section. However, for the TeV scale DM, we have to rely on the Cherenkov Telescope Array, which is able to rule out the whole parameter space except for the coannihilation region.

Dark Matter physics in general NMSSM

In the General Next-to-Minimal Supersymmetric Standard Model (GNMSSM), singlet particles may form a secluded sector of dark matter (DM), in which Singlino-like DM could achieve the observed relic abundance through various channels such as χ~10χ~10→hshs\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\overset{\\sim }{\\chi}}_1^0{\\overset{\\sim }{\\chi}}_1^0\ o {h}_s{h}_s $$\\end{document}, AsAs, hsAs, where hs and As represent singlet-dominated CP-even and CP-odd Higgs bosons. We provide analytical formulas for both the spin-independent and spin-dependent cross sections of Singlino DM scattering with nucleons, illustrating their dependence on the model’s parameters in a clear manner. We also present analytic expressions for the annihilation cross sections of these three important channels. Based on these preparations, we conducted Bayesian analyses of the GNMSSM and concluded that the theory significantly favored Singlino-dominated DM over Bino-like DM across a much broader range of parameters. The combined results from our numerical analyses and the formulas distinctly highlight crucial aspects of DM physics within the GNMSSM.

NLO thermal corrections to dark matter annihilation cross sections: A novel approach

NLO thermal corrections to dark matter annihilation cross sections: A novel approach

Constraints on Ultraheavy Dark Matter Properties from Dwarf Spheroidal Galaxies with LHAASO Observations.

In this Letter we try to search for signals generated by ultraheavy dark matter at the Large High Altitude Air Shower Observatory (LHAASO) data. We look for possible γ rays by dark matter annihilation or decay from 16 dwarf spheroidal galaxies in the field of view of the LHAASO. Dwarf spheroidal galaxies are among the most promising targets for indirect detection of dark matter that have low fluxes of astrophysical γ-ray background while having large amount of dark matter. By analyzing more than 700days of observational data at LHAASO, no significant dark matter signal from 1TeV to 1EeV is detected. Accordingly we derive the most stringent constraints on the ultraheavy dark matter annihilation cross section up to EeV. The constraints on the lifetime of dark matter in decay mode are also derived.

Determination of dark matter distribution in Ursa Major III and constraints on dark matter annihilation* *Supported by the National Natural Science Foundation of China (11947005, 12175248, 12205388, 12227804), the Science & Technology Development Fund of Tianjin Education Commission for Higher Education (2020KJ003), and the PhD Research Startup Foundation of Tianjin Normal University (52XB1912)

The recently discovered satellite dwarf galaxy Ursa Major III provides a promising opportunity to explore the signatures resulting from dark matter (DM) annihilation owing to its proximity and large J-factor. Given the absence of an excess of γ-ray signatures originating from Ursa Major III, observations of γ-rays, such as those from Fermi-LAT, can be utilized to set constraints on the DM annihilation cross-section. In this study, we determined the DM density profile and considered the relationship between DM density and velocity dispersion at different locations within Ursa Major III through Jeans analysis. We calculated the J-factor of Ursa Major III for s-wave annihilation along with the effective J-factors for p-wave and Sommerfeld enhanced annihilation scenarios. Employing these derived J-factors, we set stringent constraints on DM annihilation cross-sections in three scenarios. Given the substantial impact of member star identification on the J-factor of Ursa Major III, we further calculated J-factors under the exclusion of the largest velocity outlier. Our analysis reveals a notable reduction in the median value and an increase in the deviation of J-factors, thereby leading to considerably weaker constraints.

Time-variable diffuse γ-ray foreground

ABSTRACT While the data analysis of γ-ray telescopes has now become more robust, some signals may be misinterpretations of a time-variable foreground emission from the Solar system, induced by low-energy cosmic-ray interactions with asteroids. Our goal is to provide emission templates for this time-variable diffuse γ-ray foreground by considering the populations of Main Belt Asteroids, Jovian and Neptunian Trojans, Kuiper Belt Objects, and the Oort Cloud. We model the spatial distribution of all known asteroids by performing 3D-fits to determine their density profiles and calculate their appearances by line-of-sight integrations. Because Earth and the asteroids are moving with respect to each other, we obtain diffuse emission templates varying on time-scales of days to decades. We find that the temporal variability can lead to flux enhancements that may mimic emission features unless properly taken into account. This variation is further enhanced by the Solar cycle as the cosmic-ray spectrum is attenuated by the Solar modulation potential, leading to a relative flux increase of the outer asteroids. The cumulative effect of the time-dependent emission is illustrated for the case of the ‘511 keV OSSE fountain’, and for emission features near the Galactic Centre, both being possible misinterpretations of the Solar system albedo. We recommend that γ-ray data analyses should always take into account the possibility of a time-variable foreground. Due to the ecliptic overlap with the Galactic plane, the Galactic emission is expected to be weaker by 0.1–20 per cent, depending on time (relative planetary motion), energy, and Solar cycle, which has consequences for the interpretation of dark matter annihilation cross sections, cosmic-ray spectra and amplitudes, as well as nucleosynthesis yields and related parameters.

Asymmetric dark matter and Sommerfeld enhancement

We study the relic density of asymmetric dark matter with long-range interactions by considering the Sommerfeld effect. We find that the annihilation cross section of asymmetric dark matter is enhanced by the Sommerfeld effect and thus the relic density is decreased. Then we use the Planck data to constrain the asymmetry factor, coupling, and to derive the upper bounds on the dark matter mass in s-wave and p-wave annihilation cases.

Effective field theories for dark matter pairs in the early universe: center-of-mass recoil effects

For non-relativistic thermal dark matter, close-to-threshold effects largely dominate the evolution of the number density for most of the times after thermal freeze-out, and hence affect the cosmological relic density. A precise evaluation of the relevant interaction rates in a thermal medium representing the early universe includes accounting for the relative motion of the dark matter particles and the thermal medium. We consider a model of dark fermions interacting with a plasma of dark gauge bosons, which is equivalent to thermal QED. The temperature is taken to be smaller than the dark fermion mass and the inverse of the typical size of the dark fermion-antifermion bound states, which allows for the use of non-relativistic effective field theories. For the annihilation cross section, bound-state formation cross section, bound-state dissociation width and bound-state transition width of dark matter fermion-antifermion pairs, we compute the leading recoil effects in the reference frame of both the plasma and the center-of-mass of the fermion-antifermion pair. We explicitly verify the Lorentz transformations among these quantities. We evaluate the impact of the recoil corrections on the dark matter energy density. Our results can be directly applied to account for the relative motion of quarkonia in the quark-gluon plasma formed in heavy-ion collisions. They may be also used to precisely assess thermal effects in atomic clocks based on atomic transitions; the present work provides a first field theory derivation of time dilation for these processes in vacuum and in a medium.

Observability of CMB spectrum distortions from dark matter annihilation

Even after dark matter chemically freezes out in the early universe, electromagnetic cascades from dark matter annihilation can still perturb the background photon spectrum when the universe temperature cools down to 0.5 keV. We revisit the CMB spectrum distortions caused by s-wave dark matter annihilation under the updated Planck data and the future CMB sensitivity, concluding that s-wave annihilation cannot create observable distortions under forecast sensitivities of the (Super-)PIXIE missions. We further detail the case of p-wave dark matter annihilation, demonstrating the observability of the primordial μ-distortion. Taking current constraints from primordial light elements, structure formations, cosmic electron-positron rays, and gamma rays, we find that the μ-distortion reaching the observational limit as large as μ ≃ 3 × 10-8 can only be realized with a dark matter mass at 10–50 MeV and a kinetic decoupling temperature around 1 keV. The upper bound of the p-wave annihilation cross section can be strengthened by an order of magnitude if the μ-distortion is not detected.

Production of Dark Sector Particles via Resonant Positron Annihilation on Atomic Electrons.

Resonant positron annihilation on atomic electrons provides a powerful method to search for light new particles coupled to e^{+}e^{-}. Reliable estimates of production rates require a detailed characterization of electron momentum distributions. We describe a general method that harnesses the target material Compton profile to properly include electron velocity effects in resonant annihilation cross sections. We additionally find that high-Z atoms can efficiently act as particle physics accelerators, providing a density of relativistic electrons that allows one to extend by several times the experimental mass reach.

Light thermal dark matter beyond p-wave annihilation in minimal Higgs portal model

This study explores a minimal renormalizable dark matter (DM) model, incorporating a sub-GeV Majorana DM and a singlet scalar particle ϕ. Using scalar and pseudo-scalar interactions (couplings cs and cp), we investigate implications for DM detection, considering s-wave, p-wave, and combined (s+p wave) contributions in DM annihilation cross-section, as well as loop-correction contributions to DM-nucleon elastic scattering. Identifying a broad parameter space (10 MeV < mχ ≲ mϕ) within the 2σ allowed region, we explore scenarios (|cs| ≫ |cp|, |cs| ≪ |cp|, and |cs| ≈ |cp|). We find that (i) a non-zero pseudo-scalar coupling alleviates direct detection constraints as a comparison with the previous pure scalar coupling case; (ii) CMB observations set stringent limits on pseudo-scalar interaction dominant cases, making s-wave annihilation viable only for mχ > 1 GeV; (iii) the preferred ϕ-resonance region can be tested in the future indirect detection experiments, such as e-ASTROGAM.

Constraints on dark matter and astrophysics from tomographic γ -ray cross-correlations

We study the cross-correlation between maps of the unresolved γ-ray background constructed from the 12-year data release of the Large-Area Telescope, and the overdensity of galaxies in the redshift range z≲0.4 as measured by the 2MASS photometric redshift survey and the WISE-SuperCOSMOS photometric survey. A signal is detected at the 8−10σ level, which we interpret in terms of both astrophysical γ-ray sources, and weakly interacting massive particles (WIMP) dark matter decay and annihilation. The sensitivity achieved allows us to characterise the energy and redshift dependence of the signal, and we show that the latter is incompatible with a pure dark matter origin. We thus use our measurement to place an upper bound on the WIMP decay rate and the annihilation cross section, finding constraints that are competitive with those found in other analyses. Our analysis is based on the extraction of clean model-independent observables that can then be used to constrain arbitrary astrophysical and particle physics models. In this sense we produce measurements of the γ-ray emissivity as a function of redshift and rest-frame energy ϵ, and of a quantity F(ϵ) encapsulating all WIMP parameters relevant for dark matter decay or annihilation. We make these measurements, together with a full account of their statistical uncertainties, publicly available. Published by the American Physical Society 2024

Detecting boosted dark photons with gaseous detectors

We search for indirect signals of O(keV) dark matter annihilating or decaying into O(eV) dark photons. These dark photons will be highly boosted, predominantly transversely polarized, have decay lengths larger than the Milky Way, and can be absorbed by neutrino or dark matter experiments at a rate dependent on the photon-dark photon kinetic mixing parameter and the optical properties of the experiment. We show that current experiments cannot probe new parameter space, but future large-scale gaseous detectors with low backgrounds (i.e., CYGNUS, NEXT, PANDAX-III) may be sensitive to this signal when the annihilation cross section is especially large. Published by the American Physical Society 2024

Minimal mass of thermal dark matter and the viability of millicharged particles affecting 21-cm cosmology

Thermal freeze-out offers an attractive explanation of the dark matter density free from fine-tuning of initial conditions. For dark matter with a mass below tens of MeV, photons, electrons, and neutrinos are the only available direct Standard Model annihilation products. Using a full three-sector abundance calculation, we determine the minimal mass of dark matter, allowing for an arbitrary branching into electrons/photons and neutrinos that is compatible with current cosmological observations. The analysis takes into account the heat transfer between the various sectors from annihilation elastic scattering, representing the first fully self-consistent analysis that tracks the respective sectors’ temperatures. We thereby provide accurate thermal annihilation cross sections, particularly for velocity-dependent cases, and deduce the sensitivity of current and upcoming CMB experiments to MeV thermal dark matter. In the latter context, we also establish the fine-tuned parameter region where a tiny admixture of neutrinos in the final states rules in MeV-scale p-wave annihilating DM into electrons. Finally, we show that a sub-% millicharged dark matter with an interaction strength that interferes with 21-cm cosmology is still allowed when freeze-out is supplemented with annihilation into neutrinos. For all cases considered, we provide concrete particle physics models and supplement our findings with a discussion of other relevant experimental results. Published by the American Physical Society 2024