arXiv subjects

Purusottam Ghosh

Publications and source records attributed to Purusottam Ghosh.

At least 19 recordsLinked to original sources

arXiv2026

SN1987A Constraints of Light $\boldsymbol{Z'}$ with Non-Mixing Polarisations

The observation of supernova 1987A (SN1987A) provides a unique opportunity to explore new physics beyond the Standard Model (BSM). The production of new particles in the supernova core could accelerate the cooling process, leading to additional energy loss and consequently reducing the duration of the observed neutrino burst at detectors. Therefore, any BSM interactions that affect supernova cooling are subject to stringent constraints from SN1987A observations. In this paper, we revisit the constraints on light gauge bosons (LGBs) by reassessing the validity of underlying assumptions about the polarisation intermixing. We argue that the intermixing between different polarisation modes is suppressed in the low coupling regime. Using the light gauge boson in the $L_\mu-L_\tau$ model as an example, we find that considering the independent energy transport of longitudinal and transverse polarisations can lead to significant modifications of the SN1987A bounds on the parameter space.

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arXiv2025

Exploring two component doublet dark matter

We propose a two-component dark matter (DM) scenario by extending the Standard Model with two additional $SU(2)_L$ doublets, one scalar, and another fermion. To ensure the stability of the DM components, we impose a global $Z_2 \times Z_2^\prime$ symmetry. The lightest neutral states for both the scalar and fermion, which are non-trivially transformed under the extended symmetry, behave as stable two-component DM candidates. While single components are under-abundant due to their gauge interactions, in a mass region between $m_W$ and $525$ GeV for the scalar and a mass below $1200$ GeV for the fermion, and the fermion DM conflicts with direct detection limits over the whole parameter space, having two components helps to saturate relic density in the regions with under-abundance. Compliance with direct detection constraints leads to two options, either introducing dim-5 effective operators, or embedding the scenarios into a complete UV theory, which reproduces a type II seesaw model, thus naturally including neutrino masses. We analyze the consequences of this scenario at the LHC.

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arXiv2024

A singlet scalar assisted $N_{2}$ Leptogenesis and Pseudo-Scalar Dark Matter

We study the Leptogenesis and Dark Matter in the presence of an extra singlet complex scalar field in an extended discrete $\mathcal{Z_{\rm 3}}$ symmetry. The vacuum expectation value of the new scalar spontaneously breaks the $\mathcal{Z_{\rm 3}}$ symmetry. A remnant CP-like $\mathcal{Z_{\rm 2}}$ symmetry stabilizes the imaginary part of the complex scalar field which can act as a pseudo-Goldstone DM. The real part of the complex scalar couples to RHN opens up new decay channels which can lead to a larger CP-violation in generating the lepton asymmetry. Thus the singlet complex scalar plays a crucial role in understanding the Leptogenesis and Dark Matter parameter space. This singlet complex scalar is also responsible for the First-Order Phase Transition (FOPT) which may provide observable stochastic Gravitational wave signatures. We discuss the possible correlations among these three phenomena.

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arXiv2024

The $N_{\rm eff}$ at CMB challenges $U(1)_X$ light gauge boson scenarios

The relativistic degrees of freedom ($N_{\rm eff}$) is one of the crucial cosmological parameters. The precise measurement of $N_{\rm eff}$ at the time of cosmic microwave background formation, by Planck 2018 can be used to understand the new fundamental interactions, in particular involving light mediators. Presence of any new particle with sufficient energy density and sizeable interactions with Standard Model particles at the temperature around $\sim$ MeV can significantly alter the neutrino decoupling and hence $N_{\rm eff}$. Thus the bound on $N_{\rm eff}$ can place stringent constraints on various beyond Standard Model paradigms involving light particles. $U(1)_X$ models are among such scenarios and are widely studied in several aspects. In this work, we consider several popular $U(1)_X$ models with light $Z'$ boson like $U(1)_{B-L}$, $U(1)_{B - 3L_i}$, $U(1)_{B_i - 3 L_j}$, $U(1)_{L_i - L_j}$; $i,j =1,2,3$ being the flavour indices and study their impact on $N_{\rm eff}$. We also examine the constraints from ground based experiments like Xenon1T, Borexino, trident, etc. Our analysis shows that for light mass $M_{Z'} \lesssim \mathcal{O} (\rm{MeV})$ the $N_{\rm eff}$ provides the most stringent constraints on the $Z'$ mass and coupling, far exceeding the existing constraints from other experiments.

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arXiv2023

Hubble Tension and Cosmological Imprints of $U(1)_X$ Gauge Symmetry: $U(1)_{B_3-3 L_i}$ as a case study

The current upper limit on $N_{\rm eff}$ at the time of CMB by Planck 2018 can place stringent constraints in the parameter space of BSM paradigms where their additional interactions may affect neutrino decoupling. Motivated by this fact in this paper we explore the consequences of light gauge boson ($Z'$) emerging from local $U(1)_X$ symmetry in $N_{\rm eff}$ at the time of CMB. First, we analyze the generic $U(1)_X$ models with arbitrary charge assignments for the SM fermions and show that, in the context of $N_{\rm eff}$ the generic $U(1)_X$ gauged models can be broadly classified into two categories, depending on the charge assignments of first generation leptons. We then perform a detailed analysis with two specific $U(1)_X$ models: $U(1)_{B_3-3L_e}$ and $U(1)_{B_3-3L_\mu}$ and explore the contribution in $N_{\rm eff}$ due to the presence of $Z'$ realized in those models. For comparison, we also showcase the constraints from low energy experiments like: Borexino, Xenon 1T, neutrino trident, etc. We show that in a specific parameter space, particularly in the low mass region of $Z'$, the bound from $N_{\rm eff}$ (Planck 2018) is more stringent than the experimental constraints. Additionally, a part of the regions of the same parameter space may also relax the $H_0$ tension.

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arXiv2023

Two-component dark matter : How to get the hint at collider?

We investigate ways of identifying two kinds of dark matter (DM) component particles at high-energy colliders. The strategy is to notice and distinguish double-peaks(humps) in the missing energy/transverse energy distribution. The relative advantage of looking for {\em missing energy} is pointed out, in view of the fact that the longitudinal component of the momentum imbalance becomes an added input. It thus turns out that an electron-positron collider is better suited for discovering a two-component DM scenario. Furthermore, using Gaussian fits of the distribution histograms, we develop a set of criteria to evaluate the distinguishability of the two-peaks quantitatively.

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arXiv2023

Reviving sub-TeV $SU(2)_L$ lepton doublet Dark Matter

In this work we study the hybrid kind of dark matter(DM) production mechanism where both thermal and non-thermal contribution at two different epochs set the DM relic abundance. This hybrid set up in turn shifts the parameter space of DM in contrast to pure thermal DM scenario. We review such production mechanism in the context of the $SU(2)_L$ lepton doublet dark matter ($\Psi$) augmented with an additional singlet dark scalar ($S$). The neutral component of the dark doublet can serve as a stable DM candidate and in pure thermal scenario, it is under-abundant as well as excluded from direct detection constraints due to its strong gauge interactions in the sub-TeV mass regime. However, in addition to the thermal contribution, the late time non-thermal DM production from the decay of the long-lived dark scalar $S$ helps to fulfill the deficit in DM abundance. On the other hand, the strong gauge mediated direct detection constraint can be evaded with the help of a $SU(2)_L$ triplet scalar(with $Y=2$), resulting a pseudo-Dirac DM. To realize our proposed scenario we impose a discrete $\mathcal{Z}_2$ symmetry under which both $\Psi$ and $S$ are odd while rest of the fields are even. We find the lepton doublet pseudo-Dirac DM with mass $\sim 450-1200$ GeV, compatible with the observed relic density, direct, indirect, and existing collider search constraints.

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arXiv2023

FIMP Dark Matter from Flavon Portals

We investigate the phenomenology of a non-thermal dark matter (DM) candidate in the context of flavor models that explain the hierarchy in the masses and mixings of quarks and leptons via the Froggatt-Nielsen (FN) mechanism. A flavor-dependent $U(1)_{\rm FN}$ symmetry explains the fermion mass and mixing hierarchy, and also provides a mechanism for suppressed interactions of the DM, assumed to be a Majorana fermion, with the Standard Model (SM) particles, resulting in its FIMP (feebly interacting massive particle) character. Such feeble interactions are mediated by a flavon field through higher dimensional operators governed by the $U(1)_{\rm FN}$ charges. We point out a natural stabilizing mechanism for the DM within this framework with the choice of half-integer $U(1)_{\rm FN}$ charge $n$ for the DM fermion, along with integer charges for the SM fermions and the flavon field. In this flavon portal scenario, the DM is non-thermally produced from the decay of the flavon in the early universe which becomes a relic through the freeze-in mechanism. We explore the allowed parameter space for this DM candidate from relic abundance by solving the relevant Boltzmann equations. We find that reproducing the correct relic density requires the DM mass to be in the range $(100-300)$ keV for $n=7.5$ and $(3-10)$ MeV for $n=8.5$ where $n$ is the $U(1)_{\rm FN}$ charge of the DM fermion.

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arXiv2023

CMB signature of non-thermal Dark Matter produced from self-interacting dark sector

The basic idea of this work is to achieve the observed relic density of a non-thermal dark matter(DM) and its connection with Cosmic Microwave Background (CMB) via additional relativistic degrees of freedom which are simultaneously generated during the period $T_{\rm BBN}~{\rm to}~T_{\rm CMB}$ from a long-lived dark sector particle. To realize this phenomena we minimally extend the type-I seesaw scenario with a Dirac fermion singlet($\chi$) and a complex scalar singlet ($\varphi$) which transform non-trivially under an unbroken symmetry $\mathcal{Z}_3$. $\chi$ being the lightest particle in the dark sector acts as a stable dark matter candidate while the next to lightest state $\varphi$ operates like a long lived dark scalar particle. The initial density of $\varphi$ can be thermally produced through either self-interacting number changing processes ($3 \varphi \to 2 \varphi$) within dark sector or the standard annihilation to SM particles ($2 \varphi \to 2~ {\rm SM}$). The late time (after neutrino decoupling) non-thermal decay of $\varphi$ can produce dark matter in association with active neutrinos. The presence of extra relativistic neutrino degrees of freedom at the time of CMB can have a significant impact on $\Delta \rm N_{eff}$. Thus the precise measurement of $\Delta \rm N_{ eff}$ by current PLANCK 2018 collaboration and future experiments like SPT-3G and CMB-S4 can indirectly probe this non-thermal dark matter scenario which is otherwise completely secluded due to its tiny coupling with the standard model.

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arXiv2022

Interplay among gravitational waves, dark matter and collider signals in the singlet scalar extended type-II seesaw model

We study the prospect of simultaneous explanation of tiny neutrino masses, dark matter (DM), and the observed baryon asymmetry of the Universe in a $Z_3$-symmetric complex singlet scalar extended type-II seesaw model. The complex singlet scalar plays the role of DM. Analyzing the thermal history of the model, we identify the region of the parameter space that can generate a first-order electroweak phase transition (FOEWPT) in the early Universe, and the resulting stochastic gravitational waves (GW) can be detected at future space/ground-based GW experiments. First, we find that light triplet scalars do favor an FOEWPT. In our study, we choose the type-II seesaw part of the parameter space in such a way that light triplet scalars, especially the doubly charged ones, evade the strong bounds from their canonical searches at the Large Hadron Collider (LHC). However, the relevant part of the parameter space, where FOEWPT can happen only due to strong SM doublet-triplet interactions, is in tension with the SM-like Higgs decay to a pair of photons, which has already excluded the bulk of this parameter space. On the other hand, the latest spin-independent DM direct detection constraints from XENON-1T and PANDA-4T eliminate a significant amount of parameter space relevant for the dark sector assisted FOEWPT scenarios, and it is only possible when the complex scalar DM is significantly underabundant. In short, we conclude from our analysis that the absence of new physics at the HL-LHC and/or various DM experiments in the near future will severely limit the prospects of detecting a stochastic GW at future GW experiments and will exclude the possibility of electroweak baryogenesis within this model.

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arXiv2022

Mono-X signal and two component dark matter: new distinction criteria

The identification and isolation of two WIMP dark matter (DM) components at colliders is of wide interest on the one hand but extremely challenging on the other, especially when the dominant signal of both DM components is of the mono-X type ($X=\gamma, Z, H$). After emphasizing that an $e^+e^-$ collider is more suitable for this goal, we first identify the theoretical principles that govern the occurrence of two peaks in missing energy (ME) distribution, in a double-DM scenario. We then identify a variable that rather spectacularly elicits the double-peaking behaviour, namely, the plot of bin-wise statistical significance ($S/\sqrt{B}$) against ME. Using Gaussian fits of the histograms, we apply a set of criteria developed by us, to illustrate the above points numerically for suitable benchmarks.

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arXiv2022

Distinguishing two dark matter component particles at $e^+e^-$ colliders

In this work we demonstrate that a distorted double hump like missing energy ($\slashed{E}$) or missing transverse momentum ($\slashed{E}_T$) or missing mass ($\slashed{M}$) distribution at $e^+e^-$ colliders may hint towards the presence of multipartite dark sector. We illustrate the phenomena using a two component dark matter (DM) model involving an inert scalar doublet stabilised under a $\mathcal{Z}_2$ symmetry providing a scalar DM, one vector like fermion doublet and a right handed fermion singlet both stabilised under a different $\mathcal{Z}^{'}_2$ providing a fermion DM. We indicate the region of parameter space where the production of the heavy charged particles and their subsequent decay to DM yield double peak behaviour in $\slashed{E}$ spectrum after satisfying DM constraints. Importantly, we illustrate why and how $\slashed{E}$ serves as a better variable than $\slashed{E}_T$ in distinguishing two component DM frameworks and therefore how International Linear Collider (ILC) does better than the ongoing Large Hadron Collider (LHC). We also chalk out a set of criteria to identify and segregate the second peak in $\slashed{E}$ spectrum, after a careful analysis of the corresponding Standard Model (SM) background contribution, which plays a crucial role.

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arXiv2022

Confronting dark fermion with a doubly charged Higgs in the left-right symmetric model

We consider a fermionic dark matter (DM) in the left-right symmetric framework by introducing a pair of vector-like (VL) doublets in the particle spectrum. The stability of the DM is ensured through an unbroken $\mathcal{Z}_2$ symmetry. We explore the parameter space of the model compatible with the observed relic density and direct and indirect detection cross sections. The presence of charged dark fermions opens up an interesting possibility for the doubly charged Higgs signal at LHC and ILC. The signal for the doubly charged scalar decaying into the dark sector is analyzed in multilepton final states for a few representative parameter choices consistent with DM observations.

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arXiv2021

Shedding Flavor on Dark via Freeze-in: $U(1)_{B-3L_i}$ Gauged Extensions

We consider a singlet fermionic dark matter (DM) $\chi$ in a gauged $U(1)_{B-3L_i}$ extension of the Standard Model (SM), with $i\in e\,,\mu\,,\tau$, and derive bounds on the allowed parameter space, considering its production via freeze-in mechanism. The DM communicates with the SM only through flavorful vector-portal $Z_\text{B3L}$ due to its non-trivial charge $x$ under $U(1)_{B-3L_{i}}$, which also guarantees the stability of the DM over the age of the Universe for $x\neq\{\pm 3/2,\pm 3\}$. Considering $Z_\text{B3L}$ to lie within the mass range of a few MeV up to a few GeV, we obtain constraints on the gauge coupling $g_\text{B3L}$ from the requirement of producing right relic abundance. Taking limits from various (present and future) experimental facilities, e.g., NuCal, NA64, FASER, SHiP into account, we show that the relic density allowed parameter space for the frozen in DM can be probed with $g_\text{B3L}\gtrsim 10^{-8}$ for both $m_\chi<m_\text{ZB3L}/2$ and $m_\chi\gtrsim m_\text{ZB3L}$, while $g_\text{B3L}\lesssim 10^{-8}$ remains mostly unconstrained. We also briefly comment on the implications of neutrino mass generation via Type-I seesaw and anomalous $(g-2)_\mu$ in context with $B-3L_\mu$ gauged symmetry.

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arXiv2021

Self-interacting freeze-in dark matter in a singlet doublet scenario

We examine the non-thermal production of dark matter in a scalar extended singlet doublet fermion model where the lightest admixture of the fermions constitutes a suitable dark matter candidate. The dark sector is non-minimal with the MeV scale singlet scalar, which is stable in the Universe lifetime and can mediate the self-interaction for the multi-GeV fermion dark matter mitigating the small scale structure anomalies of the Universe. If the dark sector is strongly coupled, it undergoes internal dark thermal equilibrium after freeze-in production, and we end up with suppressed relic abundance for the fermion dark matter in a radiation dominated Universe. In contrast, the presence of a modified cosmological phase in the early era drives the fermion dark matter to satisfy nearly the whole amount of observed relic. It also turns out that the assumption of an unconventional cosmological history can allow the GeV scale dark matter to be probed at LHC from displaced vertex signature with improved sensitivity.

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arXiv2021

TeV Scale Modified Type-II Seesaw and Dark Matter in a Gauged $U(1)_{\rm B-L}$ Symmetric Model

In an endeavor to explain the light neutrino masses and dark matter (DM) simultaneously, we study a gauged $U(1)_{\rm B-L}$ extension of the standard model (SM). The neutrino masses are generated through a variant of type-II seesaw mechanism in which one of the scalar triplets has a mass in a scale that is accessible at the present generation colliders. Three SM singlet right chiral fermions $\chi_{iR}$($i=e,\mu,\tau$) with $\rm B-L$ charges -4, -4, +5 are invoked to cancel the $\rm B-L$ gauge anomalies and the lightest one among these three fermions becomes a viable DM candidate as their stability is guaranteed by a remnant $\mathcal Z_2$ symmetry to which $U(1)_{\rm B-L}$ gauge symmetry gets spontaneously broken. Interestingly in this scenario, the neutrino mass and the co-annihilation of DM are interlinked through the breaking of $U(1)_{\rm B-L}$ symmetry. Apart from giving rise to the observed neutrino mass and dark matter abundance, the model also predicts exciting signals at the colliders. Especially we see a significant enhancement in the production cross-section of the TeV scale doubly charged scalar in presence of the $Z_{\rm BL}$ gauge boson. We discuss all the relevant constraints on model parameters from observed DM abundance and null detection of DM at direct and indirect search experiments as well as the constraints on the $\rm B-L$ gauge boson from recent colliders.

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arXiv2021

Scalar Multiplet Dark Matter in a Fast Expanding Universe: resurrection of the desert region

We examine the impact of a faster expanding Universe on the phenomenology of scalar dark matter (DM) associated with $SU(2)_L$ multiplets. Earlier works with radiation dominated Universe have reported the presence of desert region for both inert $SU(2)_L$ doublet and triplet DM candidates where the DM is under abundant. We find that the existence of a faster expanding component before BBN can revive a substantial part of the desert parameter space consistent with relic density requirements and other direct and indirect search bounds. We also review the possible collider search prospects of the newly obtained parameter space and predict that such region might be probed at the future colliders with improved sensitivity via a disappearing/stable charged track.

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arXiv2021

Majorana Dark Matter and Neutrino mass in a singlet-doublet extension of the Standard Model

A minimal extension of the Standard Model (SM) by a vector-like fermion doublet and three right handed (RH) singlet neutrinos is proposed in order to explain dark matter and tiny neutrino mass simultaneously. The DM arises as a mixture of the neutral component of the fermion doublet and one of the RH neutrinos, both assumed to be odd under an imposed $\mathcal{Z}_2$ symmetry. Being Majorana in nature, the DM escapes from $Z$-mediated direct search constraints to mark a significant difference from singlet-doublet Dirac DM. The other two $\mathcal{Z}_2$ even heavy RH neutrinos give rise masses and mixing of light neutrinos via Type-I Seesaw mechanism. Relic density and direct search allowed parameter space for the model is investigated through detailed numerical scan.

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