arXiv subjects

Nabarun Chakrabarty

Publications and source records attributed to Nabarun Chakrabarty.

At least 19 recordsLinked to original sources

arXiv2025

Radiative symmetry breaking in a gauged Zee-Babu model and its gravitational wave imprints

We construct a classically scale invariant version of the Zee-Babu model governed by an $U(1)_{B-L}$ gauge symmetry wherein three right handed neutrinos with identical gauge charges are present. A $\mathbb{Z}_2$ symmetry is additionally imposed such that the lightest right handed neutrino becomes a dark matter candidate. A spontaneous breakdown of the $U(1)_{B-L}$ gauge group is triggered radiatively through renormalisation group effects and the dimensionful parameters thus emerging are proportional to the corresponding breaking scale $v_{BL}$. We demonstrate in this study how the same $v_{BL}$ controls the dynamics of neutrino mass generation, lepton flavour violation and dark matter phenomenology. It is revealed that the scenario can simultaneously accommodate the observed neutrino masses and mixings, an appropriately low lepton flavour violation and the observed dark matter relic density for 10 TeV $\lesssim v_{BL} \lesssim$ 55 TeV. In addition, the very radiative nature of the set-up signals a strong first order phase transition in the presence of a non-zero temperature. Stochastic gravitational waves stemming from this phase transition are within the reach of detectors such as LISA and BBO. The scenario therefore emerges as a concrete platform to test classical scale invariance that is tied to neutrino masses and dark matter, through gravitational waves.

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arXiv2025

Radiative $H^+_{1,2}W^- Z$ vertices in flavour conserving three Higgs-doublet scenarios

A detailed calculation of the radiatively induced $H_{1,2}^+ W^- Z$ vertices is carried out in the context of flavour conserving three Higgs doublet models (3HDMs). The Type-II, lepton specific and democratic versions of the 3HDM are chosen as representative cases and the \emph{alignment limit} is adopted. We arrange the amplitudes in UV-finite and gauge-invariant subsets for a sharper understanding of the underlying one-loop structure. Factoring-in various theoretical constraints and the ones from the $h \to γγ$ signal strength and the $B \to X_s γ$ branching ratio, we compute the relevant form factors and compare them among the various 3HDM types taken. The results also indicate a sizeable increment ($\sim 100\%$) over the corresponding form factors in 2HDMs. In addition, we probe the $H_{1,2}^+ W^- Z$ vertices at the 14 TeV LHC using vector boson fusion (VBF). It is seen that production of $H_1^+$ via VBF and the subsequent $H_1^+ \to H_2^+ H_2/A_2$ decays can have $σ\times \text{BR}$ in the $\mathcal{O}$(0.1 fb) ball park. Therefore, such a cascade can shed light on the strength of the $H_1^+ W^- Z$ interaction and confirm the presence of two charged scalars thereby acting as a smoking gun signal of a 3HDM.

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arXiv2024

Fermi-ball in a multicomponent dark matter framework and its gravitational wave signatures

It has been known that under-abundant dark matter density of an inert doublet can be replenished by an additional dark matter component, say, a fermion. We find that such a scenario can lead to the formation of stable Fermi-balls through coexisting minima of the finite temperature scalar potential. More importantly, we demonstrate that the Fermi-balls contribute sizeably to the dark matter relic density. In addition, the aforesaid coexisting minima open up the possibility of a first-order phase transition. This, in turn, triggers emission of gravitational waves that can be tested at the proposed BBO and U-DECIGO detectors. Therefore, the present study becomes a concrete setup to embed Fermi-balls in a realistic two-component dark matter model, and, to test the same using gravitational wave signatures.

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arXiv2023

Thermally corrected masses and freeze-in dark matter: a case study

If coupled \emph{feebly} to the Standard Model bath, a dark matter can evade the severe constraints from the direct search experiments. At the same time, such interactions help produce dark matter via the freeze-in mechanism. The freeze-in scenario becomes more interesting if one also includes the thermal masses of the different particles involved in the dark matter phenomenology. Incorporating such thermal corrections opens up the possibility of dark matter production via forbidden channels that remain kinematically disallowed in the standard freeze-in setup. Motivated by this, we investigate such freeze-in production of the dark matter in a minimally extended $U(1)_{L_μ-L_τ}$ framework that remains consistent with the recent muon $(g-2)$ data. Here, the role of the dark matter is played by the scalar with a non-trivial charge under the additional symmetry $U(1)_{L_μ-L_τ}$. This scalar dark matter obtains a thermally corrected mass at high temperatures for a not-so-small self-coupling. We show that the thermal correction to the dark matter mass plays a significant role in the dark matter phenomenology.

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arXiv2022

Muon $g-2$ and $W$-mass in a framework of colored scalars: an LHC perspective

A color octet isodoublet can have esoteric origins and it complies with minimal flavour violation. In this study, we take a scenario where the well known Type-X Two-Higgs doublet model is augmented with a color octet isodoublet. We shed light on how such a setup can predict the recently observed value for the $W$-boson mass. We also evaluate the two-loop Barr-Zee contributions to muon $g-2$ stemming from the colored scalars. The parameter space compatible with the observed muon $g-2$ gets relaxed w.r.t. what it is in the pure Type-X 2HDM by virtue of the contribution from the colored scalars. The extended parameter region therefore successfully accounts for both the $W$-mass and muon $g-2$ anomalies successfully. Finally, a collider signature leading to $τ^+ τ^- b \bar{b}$ final state is explored at the 14 TeV LHC using both cut-based and multivariate techniques. Such a signal can confirm the existence of both colorless as well colored scalars that are introduced by this framework.

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arXiv2022

Muon g-2 in a Type-X 2HDM assisted by inert scalars: probing at the LHC

A scenario augmenting the well known Type-X Two-Higgs doublet model (2HDM) with an additional inert doublet is proposed. The Type-X 2HDM is known to offer a solution to the muon $g-2$ anomaly for a light pseudoscalar. We show that the proposed framework can accomodate a heavier pseudoscalar on account of two-loop Barr-Zee (BZ) contributions to muon $g-2$ stemming from the inert doublet. We subsequently explore an interesting $τ^+τ^- + $ missing transverse energy signal that can be used to probe the present scenario at the 14 TeV LHC.

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arXiv2022

Single-step first order phase transition and gravitational waves in a SIMP dark matter scenario

We investigate the non-zero temperature dynamics of a sub-GeV dark matter scenario freezing-out via self-interactions. As a prototype, we take up the case of a scalar dark matter species undergoing $3 \to 2$ number changing annihilations catalysed by another scalar. We study the shape of the thermal potential of this scenario in a parameter region accounting for the observed relic abundance. An analysis reveals the possibility of a first order phase transition with bubble nucleation occurring at sub-GeV temperatures. This finding can be correlated with the typical sub-GeV masses in the framework. The gravitational wave spectra associated with such a phase transition is subsequently computed.

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arXiv2022

Limiting multiple hyperchargeless scalar triplets using electroweak phase transition and other constraints

While an additional scalar multiplet over and above the Standard Model can lead to a strong electroweak phase transition, depending on its quantum numbers, it also potentially confronts crucial constraints from theory and experiments. Should there exist more than one copy of such a multiplet, it is possible to predict that number from the requirements of a strong electroweak phase transition and agreement with the latest constraints. We aim to probe this specific issue in this study in the context of $N$ degenerate scalar triplets governed by a global O$(N)$ symmetry. We fold in important constraints from $h \to γγ$ signal strength, dark matter direct detection and Landau pole behaviour. A combined analysis reveals $N \gtrsim 70$ for a strong phase transition and consistency with the constraints. We also look into possible gravitational wave signals in the parameter regions of interest.

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arXiv2022

Muon $g-2$ in a 2HDM assisted by inert scalars: probing at the ILC

A Two-Higgs doublet model (2HDM) can predict the observed muon $g-2$ for an appropriately light pseudoscalar that now faces tight constraints. However, It was shown in past that augmenting the 2HDM by an additional inert doublet can lead to an explanation to the muon $g-2$ anomaly for a much heavier pseudoscalar. In this study, we probe such a framework at the proposed International Linear Collider (ILC) using beam polarization for $\sqrt{s}$ = 1 TeV. Using multivariate techniques, we analyse the signals $e^+ e^- \rightarrow τ^+ τ^- +$ missing transverse energy and $e^+ e^- \rightarrow μ^+ μ^- + $ missing transverse energy in the lepton- and muon-specific versions of the framework respectively. Our analysis reveals that the $e^+ e^-$ machine operating at a 3000 fb$^{-1}$ luminosity predicts a 5$σ$ discovery of a pseudoscalar as heavy as 400 GeV. Comparing with the previous study, it is concluded that the ILC is a much more potent machine than the LHC in this regard.

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arXiv2022

Flavour-alignment in an $S_3$-symmetric Higgs sector and its RG-behaviour

A three Higgs-doublet model admitting an $S_3$-symmetry can predict the observed pattern of the quark masses and their mixings. However the same symmetry also introduces potential flavour-changing neutral currents at the tree level. We assume in this work that the scalar potential contains appropriate \emph{soft} $S_3$-breaking terms in order to keep the choices of the scalar masses flexible. We identify the parameters in the Yukawa Lagrangian in the quark sector responsible for such FCNCs and constrain them using data from some of the flavour physics observables like meson-decays and meson-mixings. We also validate the corresponding model parameter space with renormalisation group (RG) evaluation.

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arXiv2022

The muon $g-2$ and $W$-mass anomalies explained and the electroweak vacuum stabilised by extending the minimal Type-II seesaw

The recent precise measurement of the $W$-mass by the CDF II collaboration is indicative of new physics beyond the Standard Model. On the other hand, a resolution of the longstanding muon $g-2$ anomaly also calls for additional dynamics. In this work, we accommodate the two aforementioned anomalies in an extension of the minimal Type-II seesaw model. That is, the minimal Type-II model is augmented with an additional doubly charged scalar and vector leptons. While a chirality-flip of the vector leptons can predict the observed value of muon $g-2$, the value of the recently reported $W$-mass can also be simultaneously achieved through the oblique parameters of the model. In addition, we further show that the parameter region allowing for the simultaneous resolution of the two anomalies complies with the neutrino mass data, lepton flavour violation and electroweak vacuum stability up to the Planck scale.

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arXiv2022

Two Component Doublet-Triplet Scalar Dark Matter stabilising the Electroweak vacuum

A two-component scalar DM scenario comprising an additional scalar doublet and a $Y$ = 0 scalar triplet is proposed. Key features of the ensuing dark matter phenomenology are highlighted with emphasis on inter-conversion between the two dark matter components. For suitable choices of the model parameters, we show that such inter-conversion can explain the observed relic abundance when the doublet dark matter component has mass in the \emph{desert} region while the triplet component has sub-TeV mass. This finding is important in the context of such mass regions known to predict under-abundant relic for the standalone cases of the scalar doublet and triplet. In addition, we also show that the present scenario can stabilise the electroweak vacuum up to the Planck scale in the parameter space responsible for the requisite dark matter observables.

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arXiv2021

Doubly charged scalars and vector-like leptons confronting the muon g-2 anomaly and Higgs vacuum stability

The present work introduces new scalar and fermionic degrees of freedom to the Standard Model. While the scalar sector is augmented by a complex scalar triplet and a doubly charged scalar singlet, the fermionic sector is extended by two copies of vector-like leptons. Of these, one copy is an $SU(2)_L$ singlet while the other, an $SU(2)_L$ doublet. We explain how this combination can offer a solution to the muon g-2 anomaly and also lead to non-zero neutrino masses. In addition, it is also shown that the parameter regions compliant with the two aforementioned issues can stabilise the electroweak vacuum till the Planck scale, something not possible within the Standard Model alone.

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arXiv2021

Probing the $H^\pm W^\mp Z$ interaction at the high energy upgrade of the LHC

An $H^\pm W^\mp Z$ interaction at the tree level is common feature of new physics models that feature scalar triplets. In this study, we aim to probe the strength of the aforementioned interaction in a model-agnostic fashion at the futuristic 27 TeV proton-proton collider. We assume that the $H^\pm$ couples dominantly to ($W^\pm,Z$) and ($t,b$). We specifically study the processes that involve the $H^\pm W^\mp Z$ vertex at the production level, that is, $p p \to H^\pm j j$ and $p p \to Z H^\pm$. Moreover, we look into both $H^\pm \to W^\pm Z,~t b$ decays for either production process. Our investigations reveal that the $H^\pm j j$ production process has a greater reach compared to $Z H^\pm$. Moreover, the discovery potential of a charged Higgs improves markedly with respect to the earlier studies corresponding to lower centre-of-mass energies. Finally, we recast our results in the context of the popular Georgi-Machacek model.

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arXiv2021

Relic density of dark matter in the inert doublet model beyond leading order for the low mass region: 1. Renormalisation and constraints

The present paper is the first in a series that addresses the calculation of the full one-loop corrections of dark matter (DM) annihilation cross-sections in the low mass region of the inert doublet model (IDM). We first review the renormalisation of the model both in a fully on-shell (OS) scheme and a mixed scheme combining on-shell (for the masses) and a $\overline{\rm MS}$ approach when the partial invisible width is closed and does not allow the use of a full OS scheme. The scale dependence introduced by the mixed scheme is shown to be tracked through an analysis of a parametrisation of the tree-level cross-section and the $β$ constant of a specific coupling. We discuss how to minimise the scale dependence. The theoretical uncertainty brought by the scale dependence leads us to introduce a new criterion on the perturbativity of the IDM. This criterion further delimits the allowed parameter space which we investigate carefully by including a host of constraints, both theoretical and experimental, including in particular, new data from the LHC. We come up with a set of benchmark points that cover three different mechanisms for a viable relic density of DM: {\it i)} a dominance of co-annihilation into a fermion pair, { \it ii)} annihilation into 2 vector bosons of which one is off-shell that requires the calculation of a $2 \to 3$ process at one-loop, {\it iii)} annihilation that proceeds through the very narrow standard model Higgs resonance. Since the $2 \to 3$ vector boson channel features in all three channels and is essentially a build up on the simpler annihilation to OS vector bosons, we study the latter in detail in the present paper. We confirm again that the corrected cross-sections involve a parameter that represents rescattering in the dark sector that a tree-level computation in not sensitive to.

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arXiv2021

Relic density of dark matter in the inert doublet model beyond leading order for the low mass region: 2. Co-annihilation

We examine the relic density of the light mass dark matter region in the inert doublet model (IDM) when the dominant process is due to co-annihilation between the lightest neutral scalars of the model. The full one-loop electroweak corrections are computed in an on-shell scheme and are found to be well approximated as an effective cross-section expressed in terms of $Z$-observables. The electroweak corrections to the subdominant process which consists of an annihilation into an on-shell $W$ and an off-shell $W$, that is calculated as a annihilation into a 3-body final state, is also performed. The latter reveals an important dependence on a parameter that describes the self-interaction of the new scalars (solely within the dark sector), a parameter which is not accessible in tree-level calculations of standard model (SM)-IDM interactions.

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arXiv2021

Relic density of dark matter in the inert doublet model beyond leading order for the low mass region: 3. Annihilation in 3-body final state

We perform the first one-loop electroweak corrections for $2 \to 3$ processes for dark matter annihilation. These are the dominant processes that enter the computation of the relic density for the low mass region of the inert doublet model (IDM) when annihilations to two on-shell vector bosons are closed. The impact of the one-loop corrections are important as they involve, through rescattering effects, not only a dependence on the parameter controlling the dark sector, not present if a calculation at tree-level is conducted, but also on the renormalisation scale. These combined effects should be taken into account in analyses based on tree-level cross-sections of the relic density calculations, as a theoretical uncertainty which we find to be much larger than the cursory $\pm 10\%$ uncertainty that is routinely assumed, independently of the model parameters.

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arXiv2021

Relic density of dark matter in the inert doublet model beyond leading order for the low mass region: 4. The Higgs resonance region

One-loop electroweak corrections to the annihilation cross-sections of dark matter in the Higgs resonance region of the inert doublet model (IDM) are investigated. The procedure of how to implement the width of the Higgs in order to regularise the amplitude both at tree-level and at one-loop together with the renormalisation of a key parameter of the model, are thoroughly scrutinised. The discussions go beyond the application to the relic density calculation and also beyond the IDM so that addressing these technical issues can help in a wider context. We look in particular at the dominant channels with the $b \bar b$ final state and the more involved 3-body final state, $W f \bar f^\prime$, where both a resonance and an anti-resonance, due to interference effects, are present. We also discuss how to integrate over such configurations when converting the cross-sections into a calculation of the relic density.

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