Annihilation Channels Research Articles

Constraints on annihilating dark matter in the Omega Centauri cluster

Recent gamma-ray and radio studies have obtained some stringent constraints on annihilating dark matter properties. However, only a few studies have focused on using x-ray data to constrain annihilating dark matter. In this article, we perform the x-ray analysis of annihilating dark matter using the data of the Omega Centauri cluster. If dark matter is the correct interpretation of the nonluminous mass component derived in the Omega Centauri cluster, the conservative lower limits of thermal dark matter mass annihilating via the ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$, $b\overline{b}$, and ${W}^{+}{W}^{\ensuremath{-}}$ channels can be significantly improved to 104(43) GeV, 650 (167) GeV, and 480(137) GeV, respectively, assuming the diffusion coefficient ${D}_{0}\ensuremath{\le}{10}^{26}({10}^{27})\text{ }\text{ }{\mathrm{cm}}^{2}/\mathrm{s}$. These constraints can safely rule out the recent claims of dark matter interpretation of the gamma-ray excess and antiproton excess seen in our Galaxy. Generally speaking, the conservative lower limits obtained for nonleptophilic annihilation channels are much more stringent than that obtained by gamma-ray analysis of nearby dwarf galaxies. We anticipate that this would open a new window for constraining annihilating dark matter.

DarkFlux: A new tool to analyze indirect-detection spectra of next-generation dark matter models

We present DarkFlux, a software tool designed to analyze indirect-detection signatures for next-generation models of dark matter (DM) with multiple annihilation channels. Version 1.0 of this tool accepts user-generated models with $2\to 2$ tree-level dark matter annihilation to pairs of Standard Model (SM) particles and analyzes DM annihilation to $\gamma$ rays. The tool consists of three modules -- the annihilation fraction module, the flux module, and the analysis module -- which can be run in a loop in order to scan over DM mass if desired. [A description of each module is available in the full abstract.] DarkFlux v1.0 compares the total $\gamma$-ray flux to a joint-likelihood analysis of fifteen dwarf spheroidal galaxies (dSphs) analyzed by the $Fermi$-LAT collaboration. DarkFlux automatically provides data tables and can plot the output of the three modules. In this manual, we briefly motivate this indirect-detection computer tool and review the essential DM physics. We then describe the several modules of DarkFlux in greater detail. Finally, we show how to install and run DarkFlux and provide two worked examples demonstrating its capabilities.

Spatial extension of dark subhalos as seen by Fermi -LAT and the implications for WIMP constraints

Spatial extension has been hailed as a "smoking gun" in the gamma-ray search of dark galactic subhalos, which would appear as unidentified sources for gamma-ray telescopes. In this work, we study the sensitivity of the Fermi-LAT to extended subhalos using simulated data based on a realistic sky model. We simulate spatial templates for a set of representative subhalos, whose parameters were derived from our previous work with N-body cosmological simulation data. We find that detecting an extended subhalo and finding an unequivocal signal of angular extension requires, respectively, a flux 2 to 10 times larger than in the case of a point-like source. By studying a large grid of models, where parameters such as the WIMP mass, annihilation channel or subhalo model are varied significantly, we obtain the response of the LAT as a function of the product of annihilation cross section times the J-factor. Indeed, we show that spatial extension can be used as an additional filter to reject subhalos candidates among the pool of unidentified LAT sources, as well as a "smoking gun" for positive identification. For instance, typical angular extensions of a few tenths of degree are expected for the considered scenarios. Finally, we also study the impact of the obtained LAT sensitivity to such extended subhalos on the achievable dark matter constraints, which are a few times less constraining than comparable point-source limits.

Investigating the role of strangeness in baryon–antibaryon annihilation at the LHC

Annihilation dynamics plays a fundamental role in the baryon–antibaryon interaction (B–B‾) at low-energy and its strength and range are crucial in the assessment of possible baryonic bound states. Experimental data on annihilation cross sections are available for the p–p‾ system but not in the low relative momentum region. Data regarding the B–B‾ interaction with strange degrees of freedom are extremely scarce, hence the modeling of the annihilation contributions is mainly based on nucleon–antinucleon (N–N‾) results, when available. In this letter we present a measurement of the p–p‾, p–Λ‾⊕p‾–Λ and Λ–Λ‾ interaction using correlation functions in the relative momentum space in high-multiplicity triggered pp collisions at s=13 TeV recorded by ALICE at the LHC. In the p–p‾ system the couplings to the mesonic channels in different partial waves are extracted by adopting a coupled-channel approach with recent χEFT potentials. The inclusion of these inelastic channels provides good agreement with the data, showing a significant presence of the annihilation term down to zero momentum. Predictions obtained using the Lednický–Lyuboshits formula and scattering parameters obtained from heavy-ion collisions, hence mainly sensitive to elastic processes, are compared with the experimental p–Λ‾⊕p‾–Λ and Λ–Λ‾ correlations. The model describes the Λ–Λ‾ data and underestimates the p–Λ‾⊕p‾–Λ data in the region of momenta below 200 MeV/c. The observed deviation indicates a different contribution of annihilation channels to the two systems containing strange hadrons.

Scale invariant scotogenic model: Dark matter and the scalar sector

In this paper, we investigate the mutual impact between the dark matter (DM) requirements and the scalar sector in the scale invariant (SI) scotogenic model. The model is motivated by the neutrino mass and DM within a classically SI framework. It is a SI generalization of the scotogenic model, where the standard model (SM) is extended by a real singlet, an inert scalar doublet and three Majorana singlet fermions, where the lightest one ($N_{1}$) could play the DM candidate role. In addition to the annihilation channels $N_{1}N_{1}\rightarrow\ell_{\alpha}\ell_{\beta},\nu_{\alpha}\bar{\nu}_{\beta}$, the DM can be annihilated via few s-channel processes into SM particles, that are mediated by the Higgs/dilaton. This allows the new Yukawa interactions, that are responsible for neutrino mass generation, to take small values and therefore avoid the mass degeneracy between the CP-even and CP-odd inert scalars unlike the case of the minimal scotogenic model. In contrast to many Majorana DM models, the DM in the SI-scotogenic model couples to the quarks at tree-level, and hence the constraint from the direct detection experiments is very important on the space parameter. The aim of this work is to investigate the correlation between the DM requirements and the scalar sector in this model.

Dark matter transient annihilations in the early Universe

The cosmological evolution can modify the dark matter (DM) properties in the early Universe to be vastly different from the properties today. Therefore, the relation between the relic abundance and the DM constraints today needs to be revisited. We propose novel \textit{transient} annihilations of DM which helps to alleviate the pressure from DM null detection results. As a concrete example, we consider the vector portal DM and focus on the mass evolution of the dark photon. When the Universe cools down, the gauge boson mass can increase monotonically and go across several important thresholds; opening new transient annihilation channels in the early Universe. Those channels are either forbidden or weakened at the late Universe which helps to evade the indirect searches. In particular, the transient resonant channel can survive direct detection (DD) without tuning the DM to be half of the dark photon mass and can be soon tested by future DD or collider experiments. A feature of the scenario is the existence of a light dark scalar.

Combined searches for dark matter in dwarf spheroidal galaxies observed with the MAGIC telescopes, including new data from Coma Berenices and Draco

Milky Way dwarf spheroidal galaxies (dSphs) are among the best candidates to search for signals of dark matter annihilation with Imaging Atmospheric Cherenkov Telescopes, given their high mass-to-light ratios and the fact that they are free of astrophysical gamma-ray emitting sources. Since 2011, MAGIC has performed a multi-year observation program in search for Weakly Interacting Massive Particles (WIMPs) in dSphs. Results on the observations of Segue 1 and Ursa Major II dSphs have already been published and include some of the most stringent upper limits (ULs) on the velocity-averaged cross-section 〈σannv〉 of WIMP annihilation from observations of dSphs. In this work, we report on the analyses of 52.1 h of data of Draco dSph and 49.5 h of Coma Berenices dSph observed with the MAGIC telescopes in 2018 and in 2019 respectively. No hint of a signal has been detected from either of these targets and new constraints on the 〈σannv〉 of WIMP candidates have been derived. In order to improve the sensitivity of the search and reduce the effect of the systematic uncertainties due to the J-factor estimates, we have combined the data of all dSphs observed with the MAGIC telescopes. Using 354.3 h of dSphs good quality data, 95% CL ULs on 〈σannv〉 have been obtained for 9 annihilation channels. For most of the channels, these results reach values of the order of 10−24cm3/s at ∼1 TeV and are the most stringent limits obtained with the MAGIC telescopes so far.

Color Transparency in p¯A Reactions

Exclusive channels of antiproton annihilation on the bound nucleon are sensitive to mesonic interactions with the target residue. If the hard scale is present, then such interactions should be reduced due to color transparency (CT). In this paper, the d(p¯,π−π0)p reaction is discussed at a large center-of-mass angle. Predictions for the future PANDA (antiProton ANnihilations at DArmstadt) experiment at FAIR (Facility for Antiproton and Ion Research, Darmstadt, Germany) are given for nuclear transparency ratios calculated within the generalized eikonal approximation and the quantum diffusion model of CT.

Resurrecting the fraternal twin WIMP miracle

In twin Higgs models that contain the minimal particle content required to address the little hierarchy problem (i.e., fraternal models), the twin tau has been identified as a promising candidate for dark matter. In this class of scenarios, however, the elastic scattering cross section of the twin tau with nuclei exceeds the bounds from XENON1T and other recent direct detection experiments. In this paper, we propose a modification to the fraternal twin Higgs scenario that we call ${\mathbb{Z}}_{2}\mathrm{FTH}$, incorporating visible and twin hypercharged scalars (with $Y=2$) which break twin electromagnetism. This leads to new mass terms for the twin tau that are unrelated to its Yukawa coupling, as well as additional annihilation channels via the massive twin photon. We show that these features make it possible for the right-handed twin tau to freeze out with an acceptable thermal relic abundance while scattering with nuclei at a rate that is well below existing constraints. Nonetheless, large portions of the currently viable parameter space in this model are within the reach of planned direct detection experiments. The prospects for indirect detection using gamma rays and cosmic-ray antiprotons are also promising in this model. Furthermore, if the twin neutrino is light, the predicted deviation of $\mathrm{\ensuremath{\Delta}}{N}_{\mathrm{eff}}\ensuremath{\approx}0.1$ would be within reach of Stage 4 cosmic microwave background experiments. Finally, the high luminosity LHC should be able to probe the entire parameter space of the ${\mathbb{Z}}_{2}\mathrm{FTH}$ model through charged scalar searches. We also discuss how searches for long-lived particles are starting to constrain fraternal twin Higgs models.

BHLS_2 upgrade: tau spectra, muon HVP and the [pi ^0,~eta ,~{eta ^prime }] system

The generic hidden local symmetry (HLS) model has recently given rise to its hbox {BHLS}_2 variant, defined by introducing symmetry breaking mostly in the vector meson sector; the central mechanism is a modification of the covariant derivative at the root of the HLS approach. However, the description of the tau dipion spectra, especially the Belle one, is not fully satisfactory, whereas the simultaneous dealing with its annihilation sector (e^+ e^- rightarrow pi ^+ pi ^-/pi ^+ pi ^-pi ^0/ pi ^0 gamma /eta gamma /K^+ K^-/K_L K_S) is optimum. We show that this issue is solved by means of an additional breaking term which also allows us to consistently include the mixing properties of the [pi ^0,eta ,{eta ^prime }] system within this extended hbox {BHLS}_2 (hbox {EBHLS}_2) scope. This mechanism, an extension of the usual ’t Hooft determinant term, only affects the kinetic energy part of the hbox {BHLS}_2 Lagrangian. One thus obtains a fair account for the tau dipion spectra which complements the fair account of the annihilation channels already reached. The Belle dipion spectrum is found to provide evidence in favor of a violation of the conserved vector current (CVC) in the tau lepton decay; this evidence is enforced by imposing the conditions <0|J_mu ^q |[q^prime overline{q^prime }](p)>=ip_mu f_q delta _{q q^prime }, { [q {overline{q}}], q=u,d,s} on hbox {EBHLS}_2 axial current matrix elements. hbox {EBHLS}_2 is found to recover the usual (completed) formulae for the [pi ^0,~eta ,~{eta ^prime }] mixing parameters, and the global fits return mixing parameter values in agreement with expectations and better uncertainties. Updating the muon hadronic vacuum polarization (HVP), one also argues that the strong tension between the KLOE and BaBar pion form factors imposes to provide two solutions, namely a_mu ^{HVP-LO}(mathrm{KLOE})=687.48 pm 2.93 and a_mu ^{HVP-LO}(mathrm{BaBar})=692.53 pm 2.95, in units of 10^{-10}, rather than some combination of these. Taking into account common systematics, their differences from the experimental BNL-FNAL average value exhibit significance > 5.4sigma (KLOE) and > 4.1sigma (BaBar), with fit probabilities favoring the former.

Phenomenology of dark matter and mirror fermions from a left–right mirror model with singlet scalar

We investigate a left–right mirror model with SU(3) c × SU(2)L × SU(2)R × U(1) Y and a discrete symmetry, which introduces mirror fields that are copies of the standard model (SM) fields. The mirror fields have the opposite chirality to their SM counterpart fields. We also introduce singlet scalars as dark matter (DM). The new interaction between DM, SM fermions, and mirror fermions can account for DM abundance, charged lepton flavor violation, lepton anomalous magnetic moment, and flavor changing neutral current. We demonstrated that if we choose DM annihilation into muon as the dominant annihilation channel for leptophilic DM, both the observed DM abundance and the observed discrepancy between theory and experiment in the muon anomalous magnetic moment can be explained without contradicting the bound derived from charged lepton flavor violating processes. We briefly discuss how mirror fermions will be produced at the future linear collider, as mirror fermions can interact with neutral gauge bosons in this model. Finally, we discuss the lightest mirror neutrino decay mechanism, which will be highly abundant if stable.

Studying QCD modeling of uncertainties in particle spectra from dark-matter annihilation into jets

Motivated by various excesses observed by the Fermi-LAT and AMS collaborations, we perform a detailed analysis of QCD uncertainties on particle spectra from dark-matter annihilation (or decay) into jets. When annihilated to SM particles, the final-state annihilation products undergo various complicated processes such as QED and QCD bremsstrahlung, hadronisation, and hadron decays. These processes contain some intrinsic uncertainties which are usually difficult to model and which are neglected in physical analyses. First, we perform several re-tunings of the fragmentation function parameters. Then, we estimate two kinds of uncertainties: (i) perturbative from QCD showers and (ii) non-perturbative from hadronisation function. The results are tabulated for a wide range of dark matter masses, mχ ∈ [5,105] GeV, and annihilation channels. They can be found on Zenodo: https://doi.org/10.5281/zenodo.3764809.

Constraining the annihilation of dark matter via cosmic-ray positrons and electrons

We aim to constrain the properties of dark matter particles by several measurements of positrons and electrons from cosmic-rays. We assume that collisions of dark matter particles and dark matter anti-particles can produce positrons and electrons. The electron-positron propagation is explained by a diffusion-loss equation including loss rates, diffusion, as well as source function. We use data of cosmic-ray positrons and electrons detected by PAMELA, H.E.S.S., AMS-02 and Fermi-LAT. We compare the observational data with the electron and positron spectrum from five annihilation channels in our model to derive constraining factors regarding the cross-section of the annihilation of dark matter. The tightest constraint is provided by cosmic-ray positrons of AMS-02 for the electron channel. Dark matter with mass below a few GeV gets excluded by the cosmic-ray positrons of AMS-02 for the electron, muon and tau channels.

Search for dark matter signals toward the irregular dwarf galaxy WLM with H.E.S.S

Cosmological and astrophysical probes suggest that dark matter (DM) makes up for 85% of the total matter of the Universe. The determination of its nature, however, remains one of the greatest challenges of fundamental Physics. In the DM indirect detection framework, Weakly Interacting Massive Particles (WIMPs) particles would produce signals by self-annihilating and creating SM products such as γ rays, which might be detected by ground-based telescopes. Dwarf irregular galaxies represent promising targets for the search for DM as they are assumed to be dark matter dominated. These dwarf irregular galaxies are rotationally supported with relatively simple and well measured kinematics which lead to small uncertainties on their dark matter distribution profiles. In 2018, the H.E.S.S. telescopes observed the irregular dwarf galaxy Wolf-Lundmark-Melotte (WLM) for 18 hours. These observations are the very first ones made by an imaging air Cherenkov telescope toward this kind of objects. We search for a DM signal looking for excess of γ rays towards WLM dwarf galaxy. We perform the first analysis of this source in stereoscopy using the data taken by the five H.E.S.S. telescopes. In this proceeding, we present the new results on the observations of WLM interpreted in terms of velocity-weighted cross-section for DM self-annihilation 〈συ〉 as a function of DM particle mχ mass for the eight annihilation channels , and γγ.

Constraining sub-GeV dark matter with the Integral data

The goal of this work is to constrain sub-GeV dark matter particles (1 MeV ≤ mDM ≤ 5 GeV) by looking at photons in the keV energy range and by including the inverse Compton scattering contribution to the total flux. In particular, the electrons and positrons produced by dark matter particles can scatter the low-energy photons in the Milky Way up to the X-ray energies. These X rays are probed by the Integral data, which we utilised to constrain the dark matter annihilation cross-section. The relevant annihilation channels are electron, muon and pion. As a result, we derived competitive bounds for dark matter particles with a mass between 150 MeV and 1.5 GeV.

Searching signals of dark matter from unidentified Fermi-LAT objects with H.E.S.S

Milky Way-sized galaxies harbor a population of unmerged dark matter subhalos, as shown from cosmological N-body simulations. These subhalos could shine in gamma-rays and be eventually detected as unidentified sources in gamma-ray surveys. From a thorough selection of unidentified Fermi-LAT Objects (UFOs), we observe four UFOs with H.E.S.S. and we search for very high-energy (VHE, E ≥ 100 GeV) gamma-ray emission. Considering dark matter masses above a few hundred GeV, the observed UFOs could be identified as dark matter subhalos, given their hard gamma-ray spectra in the few-ten-to-hundred GeV energy range. Since no significant very-high-energy gamma-ray emission is detected in any of the four UFOs dataset nor in the combined one, we derive constraints on the product of the velocity-weighted annihilation cross-section 〈συ〉 by the J-factor for the dark matter models. We derive 95% CL upper limits on 〈συ〉 J in W + W − and τ+τ− annihilation channels for the TeV dark matter particles. Considering thermal WIMPs, we derive constraints on the J-factors from the H.E.S.S. observations. Assuming model-dependent predictions from cosmological N-body simulations on the J-factor distribution for Milky Way-sized galaxies, the dark matter models with masses greater than 0.3 TeV for the UFO emissions can be ruled out at high confidence level.

The EMU view of the Large Magellanic Cloud: troubles for sub-TeV WIMPs

We present a radio search for WIMP dark matter in the Large Magellanic Cloud (LMC).We make use of a recent deep image of the LMC obtained from observations of the Australian Square Kilometre Array Pathfinder (ASKAP), and processed as part of the Evolutionary Map of the Universe (EMU) survey.LMC is an extremely promising target for WIMP searches at radio frequencies because of the large J-factor and the presence of a substantial magnetic field.We detect no evidence for emission arising from WIMP annihilations and derive stringent bounds on the annihilation rate as a function of the WIMP mass, for different annihilation channels. This work excludes the thermal cross section for masses below 480 GeV and annihilation into quarks.

Dark matter search in dwarf irregular galaxies with the Fermi Large Area Telescope

We analyze 11 years of Fermi-LAT data corresponding to the sky regions of 7 dwarf irregular (dIrr) galaxies. DIrrs are dark matter (DM) dominated systems, proposed as interesting targets for the indirect search of DM with gamma rays. The galaxies represent interesting cases with a strong disagreement between the density profiles (core vs. cusp) inferred from observations and numerical simulations. In this work, we addressed the problem by considering two different DM profiles, based on both the fit to the rotation curve (in this case a Burkert cored profile) and results from N-body cosmological simulations (i.e., NFW cuspy profile). We also include halo substructures in our analysis, which is expected to boost the DM signal a factor of ten in halos such as those of dIrrs. For each DM model and dIrr, we create a spatial template of the expected DM-induced gamma-ray signal to be used in the analysis of Fermi-LAT data. No significant emission is detected from any of the targets in our sample. Thus, we compute upper limits on the DM annihilation cross-section versus mass parameter space. Among the 7 dIrrs, we find IC10 and NGC6822 to yield the most stringent individual constraints, independently of the adopted DM profile. We also produce combined DM limits for all objects in the sample, which turn out to be dominated by IC10 for all DM models and annihilation channels, i.e. $b\bar{b}$, $\tau^+\tau^-$ and $W^+W^-$. The strongest constraints are obtained for $b\bar{b}$ and are at the level of $\langle\sigma v \rangle \sim 7 \times 10^{-26}\text{cm}^{3}\text{s}^{-1}$ at $m_\chi\sim 6$ GeV. Though these limits are a factor of 3 higher than the thermal relic cross section at low WIMP masses, they are independent from and complementary to those obtained by means of other targets.

Heavy Higgs bosons in 2HDM at a muon collider

We study the discovery potential of the non-Standard Model (SM) heavy Higgs bosons in the Two-Higgs-Doublet Models (2HDMs) at a multi-TeV muon collider and explore the discrimination power among different types of 2HDMs. We find that the pair production of the non-SM Higgs bosons via the universal gauge interactions is the dominant mechanism once above the kinematic threshold. Single Higgs boson production associated with a pair of heavy fermions could be important in the parameter region with enhanced Yukawa couplings. For both signal final states, ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ annihilation channels dominate over the vector boson fusion (VBF) processes, except at high center of mass energies where the VBF processes receive large logarithmic enhancement with the increase of energies. Single Higgs boson $s$-channel production in ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$-annihilation via the radiative return can also be important for the Type-L 2HDM in the very large $\mathrm{tan}\ensuremath{\beta}$ region, extending the kinematic reach of the heavy Higgs boson mass to the collider energy. Considering both the production and decay of non-SM Higgs bosons, signals can be identified over the Standard Model backgrounds. With the pair production channels via annihilation, 95% C.L. exclusion reaches in the Higgs mass up to the production mass threshold of $\sqrt{s}/2$ are possible when channels with different final states are combined. Including single production modes can extended the reach further. Different types of 2HDMs can be distinguishable for moderate and large values of $\mathrm{tan}\ensuremath{\beta}$.

Multimessenger constraints on the dark matter interpretation of the Fermi -LAT Galactic Center excess

An excess of $\gamma$ rays in the data measured by the Fermi Large Area Telescope in the direction of the Galactic center has been reported in several publications. This excess, labeled as the Galactic center excess (GCE), is detected analyzing the data with different interstellar emission models, point source catalogs and analysis techniques. The characteristics of the GCE, recently measured with unprecedented precision, are all compatible with dark matter particles (DM) annihilating in the main halo of our Galaxy, even if other interpretations are still not excluded. We investigate the DM candidates that fit the observed GCE spectrum and spatial morphology. We assume a simple scenario with DM annihilating into a single channel but we inspect also more complicated models with two and three channels. We perform a search for a $\gamma$-ray flux from a list of 48 Milky Way dwarf spheroidal galaxies (dSphs) using state-of-the-art estimation of the DM density in these objects. Since we do not find any significant signal from the dSphs, we put upper limits on the annihilation cross section that result to be compatible with the DM candidate that fits the GCE. However, we find that the GCE DM signal is excluded by the AMS-02 $\bar{p}$ flux data for all hadronic and semi-hadronic annihilation channels unless the vertical size of the diffusion halo is smaller than 2 kpc -- which is in tension with radioactive cosmic ray fluxes and radio data. Furthermore, AMS-02 $e^+$ data rule out pure or mixed channels with a component of $e^+ e^-$. The only DM candidate that fits the GCE spectrum and is compatible with constraints obtained with the combined dSphs analysis and the AMS-02 $\bar{p}$ and $e^+$ data annihilates purely into $\mu^+\mu^-$, has a mass of 60 GeV and roughly a thermal cross section.