arXiv subjects

Divya Sachdeva

Publications and source records attributed to Divya Sachdeva.

At least 19 recordsLinked to original sources

arXiv2026

From Thermal History to Multi-Messenger Signatures in $\mathbb{Z}_3$ Symmetric Dark Sector

We investigate a $\mathbb{Z}_3$-symmetric extension of the Standard Model consisting of a right-handed neutrino ($N_R$), a dark fermion ($\chi$) that dominates the relic density and a dark complex scalar ($S$) that facilitates a strong first-order electroweak phase transition (SFOEWPT). The observed relic abundance, is achieved through the combined effects of annihilation, semi-annihilation, and dark-sector conversion processes over a broad region of parameter space consistent with a SFOEWPT. We further investigate the resulting multi-messenger signatures, including loop-induced direct detection, indirect detection through gamma-ray observations, and gravitational wave signals, with the latter lying within the projected sensitivities of future space-based detectors such as LISA, BBO, and DECIGO.

hep-ph↗

arXiv2026

Suppressed Magnetogenesis from Ultralight Dark Matter due to Finite Conductivity

Recently, a mechanism for generating astrophysically relevant magnetic fields via ultralight pseudoscalar dark matter, through the coupling term $g_{\phi \gamma} \phi F_{\mu \nu}\tilde{F}^{\mu\nu}$ in the Lagrangian density, was proposed in Brandenberger et al (2026) (see Ref. 1). In this scenario, the electromagnetic fields are amplified through the phenomena of parametric resonance due to the oscillatory behaviour of the pseudoscalar field. However, the analysis presented in that work does not account for the effects of a conducting medium. In this paper, we incorporate the finite conductivity of the plasma into the dynamics of the pseudoscalar and electromagnetic fields. We show that, due to the large conductivity relative to the Hubble parameter, the amplification of the electromagnetic fields due to parametric resonance is significantly suppressed. Consequently, we find that, for observationally viable values of the coupling between the electromagnetic field and the ultralight pseudoscalar field, it is not possible to generate magnetic fields of sufficient strength to explain their presence in cosmic voids.

astro-ph.CO↗

arXiv2024

Neutrino Nonstandard Interactions and Lepton Flavor Universality violation at SND@LHC via charm production

In this work, we explore the effect of neutrino nonstandard interactions (NSI) involving the charm quark at SND@LHC. Using an effective description of new physics in terms of four-fermion operators involving a charm quark, we constrain the Wilson coefficients of the effective interaction from two and three-body charmed meson decays. In our fit, we include charmed meson decays not only to pseudoscalar final states but also to vector final states and include decays to the $\eta$ and $\eta^\prime$ final states. We also consider constraints from charmed baryon decays. We then study the effect of new physics in neutrino scattering processes, involving charm production at SND@LHC, for various benchmark new physics couplings obtained from the low energy fits. Finally, we also study the effects of lepton universality violation (LUV) assuming that the new physics coupling is not lepton universal.

hep-ph↗

arXiv2023

Dark Matter spikes around Sgr A* in $\gamma$-rays

We use H.E.S.S. $\gamma$-ray observations of Sgr A* to derive novel limits on the Dark Matter (DM) annihilation cross-section. We quantify their dependence on uncertainties i) in the DM halo profile, which we vary from peaked to cored, and ii) in the shape of the DM spike around Sgr A*, dynamically heated by the nuclear star cluster. For peaked halo profiles and depending on the heating of the spike, our limits are the strongest existing ones for DM masses above a few TeV. Our study contributes to assessing the influence of the advancements in our knowledge of the Milky Way on determining the properties of DM particles.

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arXiv2022

Blazar boosted Dark Matter -- direct detection constraints on $\sigma_{e\chi}$ : Role of energy dependent cross sections

Elastic collisions with relativistic electrons from the blazar's jet can accelerate dark matter (DM) particles in the DM spike surrounding the supermassive black hole at its center. This can allow one to set stringent limits on the DM-electron scattering cross section ($\bar{\sigma}_{e\chi}$) for DM masses less than 100 MeV. We consider DM particles boosted by energetic electrons in the jets of the blazars TXS 0506+056 and BL Lacertae. Both vector and scalar mediators for the scattering of electron and electrophilic fermionic DM are studied. We highlight that the ensuing energy dependency of the S-matrix for the corresponding Lorentz structure of the vertex significantly modifies the constraints. We find that the revised exclusion limits are orders of magnitude stronger than the equivalent results for the simple constant cross section assumption. Our limits are also assessed for the less cuspy spike.

hep-ph↗

arXiv2022

Bounds on boosted dark matter from direct detection: The role of energy-dependent cross sections

The recoil threshold of Direct Detection experiments limits the mass range of Dark Matter (DM) particles that can be detected, with most DD experiments being blind to sub-MeV DM particles. However, these light DM particles can be boosted to very high energies via collisions with energetic Cosmic Ray electrons. This allows Dark Matter particles to induce detectable recoil in the target of Direct Detection experiments. We derive constraints on scattering cross section of DM and electron, using XENONnT and Super-Kamiokande data. Vector and scalar mediators are considered, in the heavy and light regimes. We discuss the importance of including energy dependent cross sections (due to specific Lorentz structure of the vertex) in our analysis, and show that the bounds can be significantly different than the results obtained assuming constant energy-independent cross-section, often assumed in the literature for simplicity. Our bounds are also compared with other astrophysical and cosmological constraints.

hep-ph↗

arXiv2022

Semi-Annihilation of Fermionic Dark Matter

The continued non-observation of events emanating from dark matter (DM) annihilations in various direct and indirect detection experiments calls into question the mechanism for determining the relic density of a weakly interacting massive particle. However, if the relic density is determined primarily by a semi-annihilation process, as opposed to the usual annihilation, this tension can be ameliorated. Here, we investigate a Z3 symmetric effective field theory incorporating a fermionic dark matter that semi-annihilates to right-handed neutrinos (RHN). The dynamics of the RHN and the impact of its late decays are also scrutinised while obtaining the correct DM relic. Finally, indirect detection bounds on the semi-annihilation cross-sections are drawn from the gamma-ray observations in the direction of Dwarf Spheroidal Galaxies (Fermi-LAT), and including the projections obtained for the H.E.S.S. and the CTA detectors.

hep-ph↗

arXiv2021

Future Constraints on Primordial Black Holes from XGIS-THESEUS

Current observations allow Primordial Black Holes (PBHs) in asteroid mass range $10^{17}-10^{22}$ g to constitute the entire dark matter (DM) energy density (barring a small mass range constrained by 21 cm observations). In this work, we explore the possibility of probing PBH with masses $10^{17}-10^{19}\,{\rm g}$ via upcoming X and Gamma Imaging Spectrometer (XGIS) telescope array on-board the Transient High-Energy Sky and Early Universe Surveyor (THESEUS) mission. While our projected limits are comparable with those proposed in the literature for $10^{16}\,{\rm g}\,<\,M_{\mathrm{PBH}}\,<\,10^{17}\,{\rm g}$, we show that the XGIS-THESEUS mission can potentially provide the strongest bound for $10^{17} \mathrm{~g}<M_{\mathrm{PBH}} \lesssim 3\times 10^{18} \mathrm{~g}$ for non-rotating PBHs. The bounds become more stringent by nearly an order of magnitude for maximally rotating PBHs in the mass range $5\times10^{15}\,{\rm g}\,<\,M_{\rm PBH}\,\lesssim\,10^{19}\,{\rm g}$.

astro-ph.CO↗

arXiv2021

Exclusion limits on Dark Matter-Neutrino Scattering Cross-section

We derive new constraints on combination of dark matter - electron cross-section ($\sigma_{\chi e}$) and dark matter - neutrino cross-section ($\sigma_{\chi \nu}$) utilising the gain in kinetic energy of the dark matter (DM) particles due to scattering with the cosmic ray electrons and the diffuse supernova neutrino background (DSNB). Since the flux of the DSNB neutrinos is comparable to the CR electron flux in the energy range $\sim 1\,{\rm MeV} - 50 \,{\rm MeV}$, scattering with the DSNB neutrinos can also boost low-mass DM significantly in addition to the boost due to interaction with the cosmic ray electrons. We use the XENON1T as well as the Super-Kamiokande data to derive bounds on $\sigma_{\chi e}$ and $\sigma_{\chi \nu}$. While our bounds for $\sigma_{\chi e}$ are comparable with those in the literature, we show that the Super-Kamiokande experiment provides the strongest constraint on $\sigma_{\chi \nu}$ for DM masses below a few MeV.

hep-ph↗

arXiv2021

$R_{K^{(\ast)}}$ from RPV-SUSY sneutrinos

We analyze the lepton flavor universality violation (LFV) in process $b\to s \ell^+\ell^-$ in an R-parity violating supersymmetric (RPV-SUSY) scenario. The most recent update on $\rk$ from the LHCb collaboration suggests approximately $3.1\sigma$ deviation from the Standard Model predictions, strengthening the case of LFV New Physics. In this work, we show that $R_{K^{(*)}}$ anomaly can be addressed via only sneutrinos within the framework of R-parity violating interactions assuming phenomenologically viable values of the couplings. While our proposed solution is by no means the only solution to these anomalies, it is a phenomenologically plausible one and, notably, quite a minimal one in the context of RPV-SUSY.

hep-ph↗

arXiv2021

Constraining Light Dark Photons from GW190517 and GW190426_152155

Ultralight dark photons predicted in several Standard Model extensions can trigger the superradiant instability around rotating black holes if their Compton wavelength is comparable to the Blackhole radius. Consequently, the angular momentum of the black hole is reduced to a value which depends upon the mass and spin of the black hole as well as the mass of the dark photon. We use the mass and spin measurements of the primary black holes in two recently observed binary black hole systems: GW190517 and GW190426_152155 to constrain dark photon mass in the ranges $1.7\times 10^{-14}{\rm\ eV}<m_{A'}<7.6\times 10^{-13}{\rm\ eV}$ and $1.3\times 10^{-13}{\rm\ eV}<m_{A'}<4.2\times 10^{-12}{\rm\ eV}$ respectively, assuming a timescale of a few million years from the time of formation of the binary black hole system to the time of their merger. We also discuss an interesting X-ray binary system, MAXI J1820_070, albeit with a relatively small value of the spin parameter.

astro-ph.HE↗

arXiv2020

Dark Matter, Muon Anomalous Magnetic Moment and the XENON1T Excess

A very economic scenario with just three extra scalar fields beyond the Standard Model is invoked to explain the muon anomalous magnetic moment, the requisite relic abundance of dark matter as well as the Xenon-1T excess through the inelastic down-scattering of the dark scalar.

hep-ph↗

arXiv2020

Constraints on Axion-Lepton coupling from Big Bang Nucleosynthesis

In this article, we study the implications of the coupling between Axion-Like-Particles (ALPs) and Leptons to cosmology, in particular, the Big Bang Nucleosynthesis (BBN). We show that the BBN, through the constraint on the effective number of relativistic neutrino species, provides the most stringent bound on the ALP-electron interaction strength for the mass of axion between 20 keV and 1 MeV. For other values of the mass, the BBN bound complements the stellar-evolution and laboratory bounds.

hep-ph↗

arXiv2019

Discussing 125 GeV and 95 GeV excess in Light Radion Model

Even if the LHC observations are consistent with the Standard model (SM), current LHC results are not precise enough to rule out the presence of new physics. Taking a contrarian view of the SM Higgs fandom, we look out for a more suitable candidate for the 125 GeV boson observed at the LHC. At the same time, a recent result from CMS hints towards an excess near 95 GeV in the diphoton ($\gamma \gamma$) channel. Given these aspects, we revisit the Higgs-radion mixing model to explore the viability of the radion mixed Higgs to be the 125 GeV boson along with the presence of a light radion (to be precise Higgs mixed radion) that can show up in future experiments in the $\gamma \gamma$ channel. We find that the mixed radion-Higgs scenario gives a better fit than the SM, with the radion mixed Higgs as a more suitable 125 GeV scalar candidate. It also gives rise to a diphoton excess from the light radion, consistent with the LHC observations.

hep-ph↗

arXiv2019

Model Independent analysis of MeV scale dark matter: II. Implications from $e^-e^+$ colliders and Direct Detection

Dark matter particles with masses in the sub-GeV range have escaped severe constraints from direct detection experiments such as LUX, PANDAX-II and XENON100 as the corresponding recoil energies are, largely, lower than the detector thresholds. In a companion paper, we demonstrated, in a model independent approach, that a significantly large fraction of the parameter space escapes the cosmological and astrophysical constraints. We show here, though, that the remaining parameter space lends itself to the possibility of discovery at both direct detection experiments (such as CRESST-II) as well as in a low-energy collider such as Belle-II.

hep-ph↗

arXiv2019

A unified explanation of $b \to s \mu^+ \mu^-$ anomalies, neutrino masses and $B\rightarrow \pi K$ puzzle

Anomalies in semi-leptonic $B$ decays could indicate new physics beyond the standard model(SM). There is an older puzzle in non-leptonic $B \to \pi K$ decays. The new particles, leptoquarks and diquarks, required to solve the semi-leptonic and the non-leptonic puzzles can also generate neutrino masses and mixing at loop level. We show that a consistent framework to explain the $B$ anomalies and the neutrino masses is possible and we make predictions for certain rare nonleptonic $B$ decays.

hep-ph↗

arXiv2019

Model Independent analysis of MeV scale dark matter: I. Cosmological constraints

Recent results from several direct detection experiments have imposed severe constraints on the multi-GeV mass window for various dark matter (DM) models. However, many of these experiments are not sensitive to MeV scale DM as the corresponding recoil energies are, largely, lower than the detector thresholds. We reexamine the light scalar DM in a model-independent approach. In this first of a two-part work, we develop an appropriate methodology to determine the effective coupling of such a DM to hadrons, thereby allowing for the determination of the corresponding annihilation rates. We find that while the parameter space can be constrained using cosmological and astrophysical observations, a significantly large fraction is still viable. In the companion paper, we study the sensitivity of both direct detection experiments as well as colliders to such a DM.

hep-ph↗

arXiv2018

Living Orthogonally: Quasi-universal Extra Dimensions

The minimal Universal Extra Dimension scenario is highly constrained owing to opposing constraints from the observed relic density on the one hand, and the non-observation of new states at the LHC on the other. Simple extensions in five-dimensions can only postpone the inevitable. Here, we propose a six-dimensional alternative with the key feature being that the SM quarks and leptons are localized on orthogonal directions whereas gauge bosons traverse the entire bulk. Several different realizations of electroweak symmetry breaking are possible, while maintaining agreement with low energy observables. This model is not only consistent with all the current constraints opposing the minimal Universal Extra Dimension scenario but also allows for a multi-TeV dark matter particle without the need for any fine-tuning. In addition, it promises a plethora of new signatures at the LHC and other future experiments.

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