arXiv subjects

Debtosh Chowdhury

Publications and source records attributed to Debtosh Chowdhury.

At least 19 recordsLinked to original sources

arXiv2026

Constraints on the inflationary vacuum and reheating era from NANOGrav

NANOGrav and various pulsar timing array experiments recently reported compelling evidence for a stochastic gravitational wave background (SGWB). Such a background may originate from several astrophysical or cosmological sources. Assuming an inflationary origin, we use the latest NANOGrav 15-year dataset to constrain inflationary parameters, including the tensor spectral index ($n_t$), tensor-to-scalar ratio ($r$), and explore the implications for reheating through constraints on the reheating equation of state ($ω_{\text{re}}$) and reheating temperature ($T_{\text{re}}$). We find a preference for an extremely blue-tilted tensor spectrum and a non-instantaneous reheating epoch. Despite no concrete evidence on primordial vacua, inflationary vacuum is commonly assumed to be the Bunch-Davies vacuum. In this work, we study modifications to the GW spectrum arising from a two-parameter Bogoliubov family of non-Bunch-Davies vacua. Within this framework, we find that NANOGrav observations favour a subclass of non-Bunch-Davies vacuum, known as the alpha-vacuum. In addition, our analysis demonstrates that the observations strikingly narrow the range of the parameter $α$ that characterizes the vacua. Our analysis indicates that the NANOGrav data can accommodate both matter- and radiation-like reheating scenarios for the standard Bunch-Davies vacuum case. However, within the non-Bunch-Davies framework considered here, a non-matter-like reheating is preferred because matter-like reheating requires relatively large $α$, violating both the NANOGrav upper bound and the backreaction constraint. We further show that a frequency-dependent parametrization of $α$ beyond a threshold frequency can yield a minimal solution that alleviates the blue-tilted issue. Finally, we highlight the possibility of testing such frequency dependence of $α$ through future GW experiments.

astro-ph.CO↗

arXiv2026

Next-to-Leading Order Unitarity Fits in the Extended Georgi-Machacek Model

We compute one-loop corrections to all $2\to2$ bosonic scattering amplitudes in the generalized two-triplet scalar extension of the Standard Model and place next-to-leading order unitarity bounds on the scalar quartic couplings of the Georgi-Machacek (GM) and the extended Georgi-Machacek (eGM) models. Further, we derive the bounded-from-below (BFB) conditions on the scalar quartic couplings demanding the stability of the scalar potential in the field subspaces. We find that, in the GM and eGM models, the BFB conditions with all combinations of three non-zero scalar fields provide a very good approximation of the all field BFB conditions while being computationally more efficient. With these improved theoretical constraints, we present results for the GM and eGM models from global fits to the latest Higgs signal strength measurements at the $13$ TeV Large Hadron Collider. We observe that the global fit disfavors the regions where $κ_V > 1.05$, $κ_V < 0.95$, and $κ_f > 1.05$, $κ_f< 0.92$ at a $95.4\%$ probability for both models. We obtain an upper limit on the absolute values of the scalar quartic couplings to be $1.91\:(3.0)$ in the GM (eGM) model. We find that the absolute mass differences between the heavy Higgs bosons are less than $410$ GeV and $520$ GeV in the GM and eGM models, respectively, if their individual masses are restricted to be below $1.1$ TeV.

hep-ph↗

arXiv2026

Addressing the Hubble tension with Sterile Neutrino Dark Matter

One of the promising dark matter (DM) candidates is a keV-scale sterile neutrino. In the early universe, the observed relic of the sterile neutrino DM is generated via the Dodelson-Widrow mechanism. However, this production scenario is severely constrained by various astrophysical observations. Many non-standard interactions between active ($ν_a$) and sterile ($ν_s$) neutrinos have been proposed to evade these astrophysical bounds. Here, we study sterile neutrinos in the context of a mass-varying scenario by coupling both active and sterile neutrinos to a scalar field. This novel mechanism opens up a new parameter space that generates the observed DM relic and addresses the Hubble tension. We find that the resulting parameter space can be fully probed by future X-ray missions.

hep-ph↗

arXiv2026

Fate of Metastable Vacua in the Type-II Two-Higgs Doublet Model

The scalar potential of the Two-Higgs-Doublet Model (2HDM) can admit multiple non-degenerate vacua due to the presence of the two Higgs doublets unlike the Standard Model (SM). For a physically viable parameter point, one of these vacua must correspond to the physical electroweak (EW) symmetry breaking vacuum with the vacuum expectation value of about $246$ GeV. Given the complex structure of the scalar potential, the physical EW vacuum may be metastable in nature rather than the global minimum of the potential. In this work, we delineate regions of the parameter space in the Type-II 2HDM accommodating multiple extrema of the scalar potential and analyze, in a gauge-independent manner, the stability of the EW vacuum there at the tree level and beyond. A Bayesian global fit of the Type-II 2HDM, including next-to-leading-order unitarity constraints and the latest experimental measurements, indicates that parameter space regions leading to metastable EW vacua are excluded at both the tree and one-loop levels.

hep-ph↗

arXiv2026

One-loop renormalization and $\boldsymbolρ$ parameter in the Georgi-Machacek model

We study the one-loop renormalization of the Georgi-Machacek model. At one loop, the renormalization of the model is phenomenologically important when triggered by operators that are absent at the tree level due to the global $SU(2)_R$ symmetry. By computing all the tree-level parameters from the standard input parameters $α_e$, $G_μ$, and $m_Z$, we show the ultraviolet divergent nature of the electroweak $ρ$ parameter when one-loop corrections are incorporated. In this model, four input parameters are required to completely parametrize the electroweak precision observables at one loop. We study the quantitative impact of the model parameters on the one-loop corrections to the $ρ$ parameter. At one loop, the $ρ$ parameter shows a mild dependence on the mass differences between the custodial fiveplet and the heavy custodial singlet, and mainly depends on the ratio of the doublet and triplet vacuum expectation values, and on the mixing angle between the custodial singlet CP-even scalars.

hep-ph↗

arXiv2025

Tagging ultra-boosted jets at FCC-hh using machine learning techniques

The Future Circular Hadron Collider (FCC-hh) will probe unprecedented energy regimes, enabling direct searches for new elementary particles at a scale of tens of TeV. FCC-hh is currently in the planning stage, and one of its primary physics goals is to search for physics beyond the Standard Model by exploring a previously inaccessible kinematic domain. While venturing into uncharted high-energy territories promises excitement, reconstructing objects with enormous transverse momenta will require overcoming major experimental challenges. This work investigates the identification of boosted $W$ bosons and boosted top quarks in the context of three beyond the Standard Model scenarios: heavy vector-like quark ($B'$), heavy neutral gauge boson ($Z'$), and heavy neutral Higgs boson ($H$). We employ machine learning techniques, including eXtreme Gradient Boosting (XGBoost) and convolutional neural networks (CNN), to identify these ultra-boosted objects in the collider from their SM background counterpart. We evaluate the performance of these techniques in distinguishing $W$ jets and top jets from QCD jets at extremely high transverse momenta ($p_{T}$) values, demonstrating their potential for future FCC-hh analyses.

hep-ph↗

arXiv2025

$\texttt{HEPfit}$: a Code for the Combination of Indirect and Direct Constraints on High Energy Physics Models

$\texttt{HEPfit}$ is a flexible open-source tool which, given the Standard Model or any of its extensions, allows to $\textit{i)}$ fit the model parameters to a given set of experimental observables; $\textit{ii)}$ obtain predictions for observables. $\texttt{HEPfit}$ can be used either in Monte Carlo mode, to perform a Bayesian Markov Chain Monte Carlo analysis of a given model, or as a library, to obtain predictions of observables for a given point in the parameter space of the model, allowing $\texttt{HEPfit}$ to be used in any statistical framework. In the present version, around a thousand observables have been implemented in the Standard Model and in several new physics scenarios. In this paper, we describe the general structure of the code as well as models and observables implemented in the current release.

hep-ph↗

arXiv2025

Dark matter cooling during early matter-domination boosts sub-earth halos

The existence of an early matter-dominated epoch prior to the Big Bang Nucleosynthesis may lead to a scenario where the thermal dark matter cools faster than plasma before the radiation-dominated era begins. In the radiation-dominated epoch, dark matter free-streams after it decouples both chemically and kinetically from the plasma. In the presence of an early matter-dominated era, chemical decoupling of the dark matter may succeed by a partial kinetic decoupling before reheating ends, depending upon the contributions of different partial wave amplitudes in the elastic scattering rate of the dark matter. We show that the s-wave scattering is sufficient to partially decouple the dark matter from the plasma, if the entropy injection during the reheating era depends on the bath temperature, while p-wave scattering leads to full decoupling in such cosmological backdrop. The decoupling of dark matter before the end of reheating causes an additional amount of cooling, reducing its free-streaming horizon compared to the usual radiation-dominated cosmology. The enhanced matter perturbations for scales entering the horizon prior to the end of reheating, combined with the reduced free-steaming horizon, increase the number density of sub-earth mass halos. The resulting boost in the dark matter annihilation signatures could offer an intriguing probe to differentiate pre-BBN non-standard cosmological epochs. We show that the free-streaming horizon of the dark matter requires to be smaller than a cut-off to ensure a boost in the sub-earth halo populations. As case studies we present two examples: one for a scalar dark matter with $s$-wave elastic scattering and the other one featuring a fermionic dark matter with $p$-wave elastic scattering. We identify regions of parameter space in both models where the dark matter kinetically decouples during reheating, amplifying small-scale structure formation.

astro-ph.CO↗

arXiv2024

SIMP dark matter during reheating

Strongly interacting massive particle (SIMP) has become one of the promising dark matter (DM) candidates due to its capability of addressing the small-scale anomaly, where the final DM abundance is set via the freeze-out of $3\rightarrow 2$ or $4\rightarrow 2$ annihilation process involving solely the dark sector particles. In this work, we explore the freeze-out of SIMP DM during the inflationary reheating epoch. During reheating, the radiation energy density evolves differently based on the shape of inflaton potential and spin of its decay products than the standard radiation-dominated picture; as a result, in this scenario, the freeze-out temperature varies distinctly with DM mass compared to the standard case. Large entropy injection due to inflaton decay demands a smaller cross-section to satisfy the observed relic than the standard radiation-dominated freeze-out case. The required cross-section, satisfying the relic density constraint and the maximum allowed thermally averaged cross-section by the unitarity of the $S$-matrix, set an upper limit on the DM mass. The upper bound on the mass of the dark matter for $3\rightarrow2$ ( $4\rightarrow2$ ) is $1$ GeV ($7$ MeV), assuming a radiation-dominated background. Interstingly, these limits get relaxed to $10^6$ ($10^4$) GeV for $3\rightarrow2$ ( $4\rightarrow2$ ) SIMP dark matter for quadratic inflaton potential. We find that a small amount of DM parameter space survives for reheating with quadratic inflaton potential after considering the lower bound of reheating temperature, put by the latest CMB observation depending on the inflationary models. In the case of the quartic inflaton potential, the allowed DM parameter space gets reduced compared to the quadratic case.

hep-ph↗

arXiv2024

Ultra-light dark matter explanation of NANOGrav observations

The angular correlation of pulsar residuals observed by NANOGrav and other pulsar timing array (PTA) collaborations show evidence in support of the Hellings-Downs correlation expected from stochastic gravitational wave background (SGWB). In this paper, we offer a non-gravitational wave explanation of the observed pulsar timing correlations as caused by an ultra-light $L_μ - L_τ$ gauge boson dark matter (ULDM). ULDM can affect the pulsar correlations in two ways. The gravitational potential of vector ULDM gives rise to a Shapiro time delay of the pulsar signals and a non-trivial angular correlation (as compared to the scalar ULDM case). In addition, if the pulsars have a non-zero charge of the dark matter gauge group, then the electric field of the local dark matter causes an oscillation of the pulsar and a corresponding Doppler shift of the pulsar signal. We point out that pulsars carry a significant charge of muons, and thus the $L_μ - L_τ$ vector dark matter contributes to both the Doppler oscillations and the time delay of the pulsar signals. The synergy between these two effects provides a better fit to the shape of the angular correlation function, as observed by the NANOGrav collaboration, compared to the standard SGWB explanation or the SGWB combined with time delay explanations. Our analysis shows that in addition to the SGWB signal, there may potentially be excess timing residuals attributable to the $L_μ - L_τ$ ULDM.

hep-ph↗

arXiv2024

Troubles mounting for multipolar dark matter

In this paper, we revisit the experimental constraints on the multipolar dark matter that has derivative coupling to the visible sector mediated by the Standard Model photon. The momentum dependent interaction enables them to be captured efficiently within massive celestial bodies boosted by their steep gravitational potential. This phenomena makes compact celestial bodies as an efficient target to probe such type of dark matter candidates. We demonstrate that a synergy of the updated direct detection results from DarkSide-50 and LUX-ZEPLIN together with IceCube bounds on high energy solar neutrinos from dark matter capture disfavour the viable parameter space of the dipolar dark matter scenario. Whereas, for the anapole dark matter scenario, a narrow window survives that lies within the reach of prospective heating signals due to the capture of dark matter at cold neutron stars.

hep-ph↗

arXiv2023

Thermalization in the presence of a time-dependent dissipation and its impact on dark matter production

In standard cosmological scenarios, a heavy meta-stable field dominates the energy density of the universe after inflation. The dissipation of this field continuously sources high-energy particles. In general, the dissipation rate of this meta-stable field can have a non-trivial time dependence. We study the impact of this time-dependent dissipation rate on the thermalization of the high-energy decay products of the meta-stable field. These energetic particles can contribute substantially to dark matter production in addition to the usual production from the thermal bath particles during reheating. We investigate the impact of this generalized dissipation on dark matter production in a model-independent way. We illustrate the parameter space that explains the observed dark matter relic abundance in various cosmological scenarios. We observed that dark matter having a mass larger than the maximum temperature attained by the thermal bath can be produced from the collision of the high-energy particles which are not yet thermalized.

hep-ph↗

arXiv2022

Fingerprints of freeze-in dark matter in an early matter-dominated era

We study the impact of an alternate cosmological history with an early matter-dominated epoch on the freeze-in production of dark matter. Such early matter domination is triggered by a meta-stable matter field dissipating into radiation. In general, the dissipation rate has a non-trivial temperature and scale factor dependence. Compared to the usual case of dark matter production via the freeze-in mechanism in a radiation-dominated universe, in this scenario, orders of magnitude larger coupling between the visible and the dark sector can be accommodated. Finally, as a proof of principle, we consider a specific model where the dark matter is produced by a sub-GeV dark photon having a kinetic mixing with the Standard Model photon. We point out that the parameter space of this model can be probed by the experiments in the presence of an early matter-dominated era.

hep-ph↗

arXiv2019

BPS solutions for generalised Wess-Zumino models and their applications

We present BPS solutions to a general class of Wess-Zumino models which extend previous results in the literature. We discuss their relation to amplitudes on threshold, and their application to scalar domain walls in Supersymmetric QCD. We also find partial expressions for Wess-Zumino models with softly broken supersymmetry.

hep-th↗

arXiv2019

Dark matter seeping through dynamic gauge kinetic mixing

We show for the first time that the loop-driven kinetic mixing between visible and dark Abelian gauge bosons can facilitate dark matter production in the early Universe by creating a 'dynamic' portal, which depends on the energy of the process. The required smallness of the strength of the portal interaction, suited for freeze-in, is justified by a suppression arising from the mass of a heavy vector-like fermion. The strong temperature sensitivity associated with the interaction is responsible for most of the dark matter production during the early stages of reheating.

hep-ph↗

arXiv2019

Forays into the dark side of the swamp

Motivated by the swampland conjectures, we study cosmological signatures of a quintessence potential which induces time variation in the low energy effective field theory. After deriving the evolution of the quintessence field, we illustrate its possible ramifications by exploring putative imprints in a number of directions of particle phenomenology. We first show that a dark matter self-interaction rate increasing with time gives a novel way of reconciling the large self interactions required to address small scale structure issues with the constraint coming from clusters. Next, we study the effects of kinetic mixing variation during the radiation dominated era on freeze-in dark matter production. Last, we elucidate quintessence effects on the restoration of the electroweak symmetry at finite temperature and the lifetime of the electroweak vacuum through a modification of the effective Higgs mass and quartic coupling.

hep-ph↗

arXiv2019

Current status of MSSM Higgs sector with LHC 13 TeV data

ATLAS and CMS collaborations have reported the results on the Higgs search analyzing $\sim 36$ fb$^{-1}$ data from Run-II of LHC at 13 TeV. In this work, we study the Higgs sector of the phenomenological Minimal Supersymmetric Standard Model, in light of the recent Higgs data, by studying separately the impact of Run-I and Run-II data. One of the major impacts of the new data on the parameter space comes from the direct searches of neutral CP-even and CP-odd heavy Higgses ($H$ and $A$, respectively) in the $H/A \to τ^{+} τ^{-}$ channel which disfavours high $\tanβ$ regions more efficiently than Run-I data. Secondly, we show that the latest result of the rare radiative decay of $B$ meson imposes a slightly stronger constraint on low $\tan β$ and low $M_A$ region of the parameter space, as compared to its previous measurement. Further, we find that in a global fit Run-II light Higgs signal strength data is almost comparable in strength with the corresponding Run-I data. Finally, we discuss scenarios with the Heavy Higgs boson decaying into electroweakinos and third generation squarks and sleptons.

hep-ph↗

arXiv2018

Moduli Portal Dark Matter

We show that moduli fields as mediators between the Standard Model and the dark sector can naturally lead to the observed relic abundance. Indeed, even if moduli are very massive, the nature of their couplings with matter and gauge fields allows producing a sufficiently large amount of dark matter in the early Universe through the freeze-in mechanism. Moreover, the complex nature of the moduli fields whose real and imaginary part couple differently to the thermal bath gives an interesting and unusual phenomenology compared to other freeze-in models of that type.

hep-ph↗