arXiv subjects

Sreemanti Chakraborti

Publications and source records attributed to Sreemanti Chakraborti.

18 recordsLinked to original sources

arXiv2026

Testing Dark Matter Coscattering with the High-Energy LZ Recoil

We investigate whether the high-energy nuclear recoil recently reported by LZ can probe dark matter (DM) whose relic abundance is set by coscattering, or conversion-driven freeze-out. We consider a singlet-doublet fermion DM model coupled to a light dark photon, in which the predominantly singlet-like DM state is separated from a more strongly interacting doublet-like state by a $\sim 100\,{\rm keV}$ mass splitting. In the small mixing regime, conversion into the doublet sector becomes the bottleneck controlling the relic abundance, realising coscattering, while the same small mixing would ordinarily suppress direct detection. A light dark photon enhances the endothermic transition $χ_1 N\toχ_2 N$, allowing the conversion-driven region to be probed by high-energy nuclear recoils. We find that for $m_{A'}=250~{\rm MeV}$ the LZ-sensitive region can cover essentially the full relic-compatible parameter space, including the dominantly conversion-driven regime. As the mediator mass is increased, the LZ sensitivity progressively shifts towards larger singlet-doublet mixing, reducing its overlap with the coscattering region. Combining the relic density and recoil requirements selects DM masses extending approximately from $750~{\rm GeV}$ to $1.6~{\rm TeV}$ for the mediator masses considered. The LZ recoil can therefore directly test the same interaction and physical parameters that dominantly set the DM relic abundance, providing a probe of the same conversion mechanism across vastly different cosmological epochs.

hep-ph↗

arXiv2026

Interplay between Electroweak Symmetry Breaking and Higgs Portal Dark Matter

Models of Dark Matter must contend with the fact that the presence of electroweak symmetry breaking along the thermal evolution of the Universe modifies the masses, interactions and, thus, the thermally averaged cross sections. We study in detail the impact of taking (not taking) the presence of the electroweak symmetry breaking into account in the calculations of the Dark Matter relic density in Higgs portal models, providing a model-independent measure of such differences. By focusing on a particular model, we show that ignoring this effect can lead to the inclusion (exclusion) of wrong (viable) regions of parameter space.

hep-ph↗

arXiv2026

Probing the Phenomenology of Dark Matter from Decoupled Freeze-Out

We consider a model of dark matter where the mediator corresponds to a superposition of a scalar and pseudoscalar, and the scenario where, after reheating, the number densities of the dark sector particles, i.e. the dark matter and the mediators, are negligible. If the coupling of the mediators to the Standard Model is feeble, but the coupling to the dark matter is large enough, the dark sector may reach equilibrium at a temperature distinct from that of the thermal bath. The relic density is then said to be obtained via decoupled freeze out (DFO). We focus on the $s$-wave annihilation scenario, which particularly benefits from the DFO mechanism by evading standard CMB limits while still yielding indirect detection signals. We calculate the relic density by solving a set of four coupled Boltzmann equations for the number densities of the dark sector particles and the energy transfer from the light to dark sector. We finally perform a thorough analysis of experimental bounds on this scenario, namely from indirect detection and the CMB, as well as from BBN, and find that, while there are considerable constraints on the parameter space where the correct relic density is obtained, a viable region remains to be explored.

hep-ph↗

arXiv2026

The COSMIC WISPers White Paper: The physics case for Weakly Interacting Slim Particles

Axions and other very weakly interacting slim particles (WISPs), with masses below 1 GeV, arise naturally in many extensions of the Standard Model of particle physics. In particular, they could offer a new framework to explain the nature of dark matter and may help address a range of puzzling observations in astrophysics and particle physics. This review provides an overview of ongoing WISP searches and outlines the prospects for the next decade, spanning their theoretical motivation, indirect signatures in astrophysical observations, and dedicated laboratory experiments. It is based on the work carried on by the EU-funded COST Action ``Cosmic WISPers in the Dark Universe: Theory, astrophysics, and experiments'' (CA21106, https://www.cost.eu/actions/CA21106). This network plays a key role in coordinating and supporting WISP searches across Europe, while also contributing to the development of a roadmap aimed at securing European leadership in this research area. It is emphasized that Europe is currently pursuing a rich, diverse, and cost-effective experimental program, with the potential to deliver one or more transformative discoveries.

hep-ph↗

arXiv2026

Lecture Notes: Probing ultralight axion-like particles with quantum technology

We review the physics of ultralight axion-like particles (ALPs) as dark matter candidates and the experimental strategies used to search for them with precision and quantum technologies. In the ultralight regime, the enormous occupation number of the dark matter field motivates a classical description in terms of a coherently oscillating background, leading to distinctive, time-dependent signatures in laboratory observables. We discuss the effective field theory framework governing ALP interactions with Standard Model fields, and show how different operators give rise to qualitatively different experimental signals. The lecture notes cover both conversion-based searches enabled by the axion-photon coupling, such as haloscopes and helioscopes, and precision experiments sensitive to oscillations of fundamental constants and material properties. These include atomic and nuclear clocks, optical cavities, laser and unequal time-delay interferometers, and mechanical or solid state resonators. Emphasis is placed on the physical origin of the sensitivity of each platform, the role of coherence, bandwidth, and noise, and the complementarity between different technologies across a wide range of ALP masses. Together, these approaches provide broad and overlapping coverage of ultralight dark matter parameter space and define a rapidly evolving experimental programme with strong discovery potential.

hep-ph↗

arXiv2026

Oscillating Resonances: Imprints of ultralight dark matter at colliders

In models where ultralight fields constitute dark matter, the misalignment mechanism leads to coherent, low-amplitude oscillations in fundamental constants. This effect arises from effective operators that couple dark matter to Standard Model fields. We present different models that can induce these effective operators by integrating out a mediator field. For mediator masses within the reach of collider searches, an alternative way to discover ultralight dark matter is to search for a resonance. Due to being a mediator to dark matter, the mass of the mediator oscillates. The resonance therefore, should not appear as a single isolated peak, but is smeared out once data is averaged over an oscillation cycle or more. Remarkably, the oscillation period and amplitude are in the range of current and future collider searches, even though constraints from atomic clocks probing variations of the fine-structure constant and the electron mass are very strong. We recast existing searches and projections from Belle II, LHCb and SHiP for an `oscillating resonance', and discuss how the periodicity of the signal can be used to reconstruct the peak from mass-binned data. We further show that time-stamped data would allow to unfold the signal via a fast Fourier transform and determine the significance of the signal for different background levels. The discovery of an oscillating resonance at a collider, with characteristics as predicted in ultralight dark matter scenarios, would constitute a powerful probe of dark matter's underlying nature.

hep-ph↗

arXiv2026

Rekindling s-Wave Dark Matter Annihilation Below 10GeV with Breit-Wigner Effects

Velocity-independent (s-wave) annihilation of thermal Dark Matter is ruled out by CMB data for masses below 10GeV, effectively ruling out the possibility of indirectly detecting it in this mass range. We demonstrate in a model-independent framework that Breit-Wigner effects from very narrow resonances can circumvent CMB constraints, thereby reviving the potential to detect s-wave DM annihilation in the present Universe. The density of resonant s-wave Dark Matter continues to evolve long after chemical decoupling, leading to a scenario we refer to as belated freeze-out, where kinetic decoupling plays a significant role in determing the relic density.

hep-ph↗

arXiv2025

On the Validity of Bounds on Light Axions for $f\lesssim10^{13}$ GeV

Light bosonic dark matter fields that can be treated like a classical wave have non-linear field values close to massive bodies. Here we make the important observation that the quadratic interactions of axion dark matter lead to non-perturbative axion field values for values of the decay constant of $f\lesssim 10^{13}$ GeV and masses $m_a\lesssim 7\times10^{8}/f\ {\rm eV^2}$ and generalise this result for axion-like particles. We identify experimental observables impacted by this effect.

hep-ph↗

arXiv2024

Axion Bounds from Quantum Technology

A consistent treatment of the quantum field theory of an axion-like particle (ALP) interacting with Standard Model fields requires to account for renormalisation group running and matching to the low-energy theory. Quantum sensor experiments designed to search for very light ALPs are particularly sensitive to these effects because they probe large values of the decay constant for which running effects become important. In addition, while linear axion interactions are set by its pseudoscalar nature, quadratic interactions are indistinguishable from scalar interactions. We show how the Wilson coefficients of linear and quadratic ALP interactions are related, including running effects above and below the QCD scale and provide a comprehensive analysis of the sensitivity of current and future experiments. We identify the reach of different experiments for the case of ALP dark matter and comment on how it could be distinguished from the case where it is not the dark matter. We present novel search strategies to observe quadratic ALP interactions via fifth force searches, haloscopes, helioscopes and quantum sensors. We emphasize the nonlinear behaviour of the ALP field close to the surface of the earth and point out which experimental results are independent on the local background field value.

hep-ph↗

arXiv2024

GeV-scale dark matter with $p$-wave Breit-Wigner enhanced annihilation

We consider a light scalar dark matter candidate with mass in the GeV range whose $p$-wave annihilation is enhanced through a Breit-Wigner resonance. The annihilation actually proceeds in the $s$-channel via a dark photon mediator whose mass is nearly equal to the masses of the incoming particles. We compute the temperature at which kinetic decoupling between dark matter and the primordial plasma occurs and show that including the effect of kinetic decoupling can reduce the dark matter relic density by orders of magnitude. For typical scalar masses ranging from 200 MeV to 5 GeV, we determine the range of values allowed for the dark photon couplings to the scalar and to the standard model particles after requiring the relic density to be in agreement with the value extracted from cosmological observations. We then show that $μ$ and $y$-distortions of the CMB spectrum and X-ray data from XMM-Newton strongly constrain the model and rule out the region where the dark matter annihilation cross-section is strongly enhanced at small dispersion velocities. Constraints from direct detection searches and from accelerator searches for dark photons offer complementary probes of the model.

hep-ph↗

arXiv2023

A Global Analysis of Resonance-enhanced Light Scalar Dark Matter

We study a minimal model for a light scalar dark matter, requiring a light scalar mediator to address the core-cusp problem and interact with the standard model particles. We analyze the model comprehensively by focusing on the Breit-Wigner resonance for dark matter annihilation and self-scattering channels, considering the thermal relic abundance condition that includes the early kinetic decoupling effect, as well as the present and future constraints from collider, direct, and indirect dark matter detections. We found that the scalar dark matter with the mass of 0.3-2 GeV remains uncharted, which will be efficiently tested by the near future MeV gamma-ray observations.

hep-ph↗

arXiv2022

Electroweak Symmetry Breaking and WIMP-FIMP Dark Matter

Electroweak Symmetry Breaking (EWSB) is known to produce a massive universe that we live in. However, it may also provide an important boundary for freeze-in or freeze-out of dark matter (DM) connected to Standard Model via Higgs portal as processes contributing to DM relic differ across the boundary. We explore such possibilities in a two-component DM framework, where a massive $U(1)_X$ gauge boson DM freezes-in and a scalar singlet DM freezes-out, that inherits the effect of EWSB for both the cases in a correlated way. Amongst different possibilities, we study two sample cases; first when one DM component freezes in and the other freezes out from thermal bath both necessarily $before$ EWSB and the second, when both freeze-in and freeze-out occur $after$ EWSB. We find some prominent distinctive features in the available parameter space of the model for these two cases, after addressing relic density and the recent most direct search constraints from XENON1T, some of which can be borrowed in a model independent way.

hep-ph↗

arXiv2021

Gamma Factory Searches for Extremely Weakly-Interacting Particles

The Gamma Factory is a proposal to back-scatter laser photons off a beam of partially-stripped ions at the LHC, producing a beam of $\sim 10$ MeV to $1$ GeV photons with intensities of $10^{16}$ to $10^{18}~\text{s}^{-1}$. This implies $\sim 10^{23}$ to $10^{25}$ photons on target per year, many orders of magnitude greater than existing accelerator light sources and also far greater than all current and planned electron and proton fixed target experiments. We determine the Gamma Factory's discovery potential through "dark Compton scattering," $γe \to e X$, where $X$ is a new, weakly-interacting particle. For dark photons and other new gauge bosons with masses in the 1~to~100 MeV range, the Gamma Factory has the potential to discover extremely weakly-interacting particles with just a few hours of data and will probe couplings as low as $\sim 10^{-9}$ with a year of running. The Gamma Factory therefore may probe couplings lower than all other terrestrial experiments and is highly complementary to astrophysical probes. We outline the requirements of an experiment to realize this potential and determine the sensitivity reach for various experimental configurations.

hep-ph↗

arXiv2021

Implications of dark sector mixing on leptophilic scalar dark matter

We propose a new viable outlook to the mixing between a singlet and a doublet leptonic dark sector fields. This choice relaxes the dark matter (DM) search constraints on the quintessential scalar singlet DM as well as presents new opportunities for its detection in the lab. The mixing produces an arbitrary mass difference between the two components of the extra doublet in a gauge-invariant way, without introducing any new scale of electroweak symmetry breaking in the theory. It also provides a useful handle to distinguish between the dark sector particles of different isospins, which is a challenging task otherwise. As the dark leptons coannihilate non-trivially, the mixing effectively enhances the viable parameter space for the relic density constraint. In low DM mass regime, our analysis shows that with a non-zero mixing, it is possible to relax the existing indirect search bounds on the upper limit of the DM-Standard Model coupling. From the analysis of the $3τ+ E^{miss}_T$ and $\ell\,τ+ E^{miss}_T$ channels for LHC at $\sqrt{s} = 13$ TeV, we show that one ensures the presence of the mixing parameter between the dark sector particles of the theory by looking at the peak and tail positions of the kinematic distributions. Even with a tweak in the values of other free parameters within the viable parameter region, the distinct peak and tail positions of the kinematic distributions remains a constant feature of the model. While both the channels present us the opportunity to detect the mixing signature at the LHC/HL-LHC, the former gives better results in terms of a larger region of mixing parameter. From the fiducial cross section, the projected statistical significance for the integrated luminosity, ${\mathscr L} = 3~\text{ab}^{-1}$, are shown for a combined parameter region obeying all the existing constraints, where there is the best possibility to detect such a signature.

hep-ph↗

arXiv2020

Multilepton signatures for scalar dark matter searches in coannihilation scenario

We revisit the scalar singlet dark matter (DM) scenario with a pair of dark lepton partners which form a vectorlike Dirac fermionic doublet. The extra doublet couples with the Standard Model (SM) leptonic doublet and the scalar singlet via a non-SM-like Yukawa structure. As a result, (i) since the extra fermionic states interact with other dark sector particles as well as the SM via gauge and Yukawa interactions, it gives rise to new DM annihilation processes including pair annihilation as well as coannihilation channels, and (ii) such a Yukawa structure opens up new production channels for leptonic final states giving much enhancement in cross sections to search for dark matter in the LHC. Using suitable kinematic observables, we train a {\em boosted decision tree} (BDT) classifier to separate enhanced but still feeble light leptonic signals from the background in an effective manner. On the other hand, the same technique is applied to study $τ$-tagged jets in the search for DM signals.

hep-ph↗

arXiv2020

Freeze-in and Freeze-out of Dark Matter with Charged Long-lived Partners

We present a novel framework capable of addressing the dark matter problem through freeze-in and freeze-out mechanisms, separately or together, depending on the region of the parameter space considered. In the dark matter dynamics, the model features an interplay of thermal production along with sizeable contribution through feeble decay of associated dark fermionic partner, which finally freezes out to the right relic density for a wide range of masses and couplings. Apart from the fermionic dark matter candidate, the model introduces two charged partners, one fermionic and another scalar, which often have delayed decays leading to distinct characteristics of such long-lived particles (LLP) in the colliders like the LHC. Our analysis shows that within the present scenario, LLP of decay length that could be probed at the LHC experiments are compatible with dark matter masses ranging from a few GeV to close to a TeV, as opposed to the requirement of keV-MeV dark matter in simple FIMP scenarios with LLP. In addition, the model presents hitherto unexplored interesting possibilities in the LLP searches, like (i) LLP to LLP to SM cascade decays, which could be searched for within the LHC detectors and (ii) heavy neutral particle decaying within MATHUSLA with two jets and large missing energy. A supplementary aspect of the model is the presence of a heavy neutrino facilitating Type-I seesaw mechanism without disturbing the dark matter side.

hep-ph↗

arXiv2019

Probing Multicomponent Extension of Inert Doublet Model with a Vector Dark Matter

Although theoretically well-motivated as a minimal consistent Dark Matter (DM) model, the Inert Doublet Model (IDM) fell short in explaining the existence of DM in the intermediate mass region ($100-500$ GeV). We try to address this problem by introducing an additional vector dark matter. We show that the relic density of inert dark matter candidate can be enhanced significantly with new interactions in the intermediate mass region $100-500$ GeV in the multicomponent dark matter model when compared with the usual single component inert doublet model. We also show that we can get a reasonable excess in the $\ /\!\!\! E_T$ distribution if we do not apply a very hard $\ /\!\!\! E_T$ cut on it as is customary in any dark matter search at the LHC.

hep-ph↗

arXiv2019

Interplay of Scalar and Fermionic Components in a Multi-component Dark Matter Scenario

We explore the multi-component dark matter (DM) scenario considered in a simple extension of the standard model with an inert scalar doublet and a singlet fermionic field providing the two DM candidates. The DM states are made stable under the unbroken $Z_2\times Z_2'$ discrete symmetry. An additional gauge singlet scalar field is introduced to facilitate the interaction of the dark fermion with the visible sector. Presence of a charged fermionic field having the same $Z_2$ charge as that of the inert scalar field allows exploring the dark matter mass regions otherwise disallowed, like in the standard Inert Doublet Model (IDM) scenarios. With these arrangements, it is shown that the light DM scenario and the desert region in the intermediate mass range of DM in the standard IDM case can be made compatible with the relic density bounds and direct detection limits. Further, detailed parameter space study is carried out keeping the coexistence of both the scalar and fermionic components in focus, showing that sizable parameter space regions are available for the entire mass range of $10\ \rm GeV \le M_{DM}\le 2000$ GeV.

hep-ph↗