arXiv subjects

Poulami Mondal

Publications and source records attributed to Poulami Mondal.

13 recordsLinked to original sources

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.

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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.

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arXiv2026

Multipolar Dark Matter Freeze-out in an Early Matter-Dominated Universe

The relic abundance of thermal dark matter depends not only on its particle interactions but also on the expansion history of the early Universe. We study the freeze-out of fermionic dark matter interacting with the Standard Model through higher-dimensional electromagnetic operators in an early matter-dominated cosmology. In particular, we consider magnetic dipole, electric dipole, anapole, and charge-radius interactions, and compute the couplings required to reproduce the observed dark matter relic abundance in the presence of entropy injection from the decay of a long-lived heavy field. The resulting parameter space is compared with that obtained in the standard radiation-dominated freeze-out scenario and confront it with current constraints from direct-detection experiments and solar neutrino observations. We find that the entropy dilution associated with an early matter-dominated epoch significantly reduces the interaction strength required to obtain the observed relic abundance, thereby rendering viable regions of parameter space that are excluded in the conventional cosmological history. Our results demonstrate that the cosmological history prior to Big Bang nucleosynthesis can have an important impact on the phenomenology and experimental viability of electromagnetic multipole dark matter.

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arXiv2026

Indications for new scalar resonances at the LHC and a possible interpretation

Over the last few years, the CMS and ATLAS collaborations at the Large Hadron Collider (LHC) have reported excesses that could hint at several new scalar resonances. Although none of them has touched the discovery level, at least two of them, at about 95 GeV and 650 GeV, have been indicated by more than one experiments, and have reached statistical significance worthy of a serious investigation. Conservatively using only the numbers given by the experimental collaborations, we find combined global significances around 3$σ$ and 4$σ$ respectively for the 95~GeV and 650~GeV putative resonances. There are some more, like the one at 320 GeV, which have also been hinted at. We show that the data on only the 650 GeV resonance, assuming they stand the test of time, predict the existence of a doubly-charged scalar, and make the more common extensions of the scalar sector like those by gauge singlet scalars, the 2-Higgs doublet models or the Georgi-Machacek model, highly disfavored. We provide the readers with a minimalistic model that may possibly explain all the indications. Such a model can also accommodate the hints of a singly charged scalar at about 375 GeV, and a doubly charged scalar at about 450 GeV, as found by both the major LHC Collaborations, the combined global significance for each of them being above $2.5σ$. We show that even the scant data, with large error bars, have the potential to strongly constrain our model containing four scalar multiplets, which makes the model easily testable and falsifiable. Our analysis comes with the obvious caveat that the allowed parameter space that we find depends on the available data on all the new resonances, and may change in future. One may also note that this is an exploratory exercise that illustrates the difficulties when it comes to fitting several resonances simultaneously, even for next-to-minimal extensions of the SM.

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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.

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arXiv2025

Light Scalars in the Extended Georgi-Machacek Model

We perform global fits of the CP-conserving Georgi-Machacek (GM) and extended Georgi-Machacek (eGM) models, incorporating a light CP-even beyond the Standard Model (BSM) scalar within the mass range of $90$ GeV to $100$ GeV. These fits combine the Higgs signal strengths and direct search limits from ATLAS and CMS at $\sqrt{s} = 8$ and $13$ TeV, $B$-physics observables, and theoretical constraints arising from next-to-leading order (NLO) unitarity and BFB constraints. From the global fit, we show that the LHC diphoton and LEP $b\bar{b}$ excesses around $95$ GeV are well compatible with the $125$ GeV Higgs data. Whereas the CMS ditau excess is incompatible with the $125$ GeV Higgs signal strength data in both the CP-conserving GM and eGM models. We present the results from the combined fit, including the $95$ GeV Higgs signal strength data. In the eGM model, the triplet VEV cannot exceed $12$ GeV for additional BSM scalar masses below $160$ GeV and approximately $20$ GeV for additional BSM scalar masses above $160$ GeV. The masses of additional BSM scalars cannot exceed $600$ GeV. The maximum mass splitting is of around $120$ GeV within the members of each custodial multiplet, and up to $250$ GeV between the members of different multiplets. In the GM model, these constraints become more stringent: the triplet VEV is limited to below $15$ GeV, which tightens to $4$ GeV once the BSM scalar masses are below $160$ GeV. Masses of the quintet $m_5$ and the triplet $m_3$ are restricted to be below $530$ GeV and $320$ GeV, respectively. A mass hierarchy, $m_5 > m_3$, is favoured in the high-mass region, with the mass splitting constrained to be less than $210$ GeV.

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arXiv2024

Resonances all over the place?

We provide a possible interpretation of excesses reported by ATLAS and CMS at around 95GeV, 650GeV and possibly 320GeV, in terms of CP-even scalars. In particular, the combined {\sl global} statistical significances of independent indications for a 650GeV object reach the $4σ$ level! While this seems sufficient incentive for a further investigation, this object cannot be fitted in tradional singlet or doublet extensions of the Standard Model. It requires by itself a larger extension with doubly-charged scalars, that naturally fits the two other excesses on top of the SM-like 125~GeV Higgs. We describe the minimal model and give some numerical illustrations.

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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.

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arXiv2022

Searches for scalars at LHC and interpretation of the findings

In view of the future Higgs factories, this work presents the status of scalar searches at the LHC with an emphasis on the H(650) resonance which has been observed in WW, ZZ and h(95)h(125) channels, with a cumulative evidence of about 7 s.d. global significance. Its interpretation in models, restricted to extension of the scalar sector by SU(2) singlets and doublets, is clearly excluded, while its interpretation in models with additional triplets requires an extension with respect to the conventional Georgi-Machacek model. A general picture of these searches is updated, showing that h(95) is also reaching a similar level of evidence while two other candidates, A(400) and h(151), although less prominent, are above the 4 s.d. global evidence.

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arXiv2022

Enhancement of the $\textbf{W}$ boson mass in the Georgi-Machacek model

The recent CDF-II measurement of the mass of the $W$ boson shows a significant tension with the Standard Model (SM) expectation, even when averaged with earlier measurements. The tension can be explained in the framework of any beyond-SM dynamics that contributes substantially to the oblique $S$ and $T$ parameters. As a typical example of such beyond-SM physics, we try to explain the tension in the framework of the Georgi-Machacek model that keeps $ρ=1$ at the tree-level, and explore the parameter space that can accommodate the $W$ mass shift. We find that a sizeable split between the custodial triplet and 5-plet of scalars can help alleviate the tension to a large extent, and raise the $W$-mass by about 30 MeV over its SM value.

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arXiv2022

Custodial symmetry, Georgi-Machacek model, and other scalar extensions

In an SU(2) gauge theory, if the gauge bosons turn out to be degenerate after spontaneous symmetry breaking, obviously these mass terms are invariant under a global SU(2) symmetry that is unbroken. The pure gauge terms are also invariant under this symmetry. This symmetry is called the {\em custodial symmetry} (CS). In $\rm SU(2)\times U(1)$ gauge theories, CS implies a mass relation between the $W$ and the $Z$ bosons. The Standard Model (SM), as well as various extensions of it in the scalar sector, possess such a symmetry. In this paper, we critically examine the notion of CS and show that there may be three different classes of CS, depending on the gauge couplings and self-couplings of the scalars. Among old models that preserve CS, we discuss the Two-Higgs Doublet Model and the one doublet plus two triplet model by Georgi and Machacek. We show that for two-triplet extensions, the Georgi-Machacek model is not the most general possibility with CS. Rather, we find, as the most general extension, a new model with more parameters and hence a richer phenomenology. Some of the consequences of this new model have also been discussed.

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arXiv2020

Hierarchy problem and dimension-six effective operators

Without any mechanism to protect its mass, the self-energy of the Higgs boson diverges quadratically, leading to the hierarchy or fine-tuning problem. One bottom-up solution is to postulate some yet-to-be-discovered symmetry which forces the sum of the quadratic divergences to be zero, or almost negligible; this is known as the Veltman condition. Even if one assumes the existence of some new physics at a high scale, the fine-tuning problem is not eradicated, although it is softer than what it would have been with a Planck scale momentum cut-off. We study such divergences in an effective theory framework, and construct the Veltman condition with dimension-six operators. We show that there are two classes of diagrams, the one-loop and the two-loop ones, that contribute to quadratic divergences, but the contribution of the latter is suppressed by a loop factor of $1/16π^2$. There are only six dimension-six operators that contribute to the one-loop category, and the Wilson coefficients of these operators play an important role towards softening the fine-tuning problem. We find the parameter space for the Wilson coefficients that satisfies the extended Veltman condition, and also discuss why one need not bother about the $d>6$ operators. The parameter space is consistent with the theoretical and experimental bounds of the Wilson coefficients, and should act as a guide to the model builders.

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arXiv2020

A 96 GeV scalar tagged to dark matter models

Recently, the CMS Collaboration observed the hint of a resonance decaying to two photons at about 96 GeV with a local significance of $2.8σ$. While it is too early to say whether this will stand the test of time, such a resonance can easily be accommodated in many extensions of the Standard Model (SM). The more challenging part is to tune such an extension so that the required number of diphoton events is reproduced. Assuming that the new resonance is a scalar, we propose that the signal may come either from an ultraviolet complete model with vectorial quarks, or a model involving gluon-scalar and photon-scalar effective operators. We then incorporate this portal to several extensions of the SM that include one or more cold dark matter candidates, and try to investigate how the existence of such a scalar resonance affects the parameter space of such models. As expected, we find that with such a scalar, the parameter space gets more constrained and hence, more tractable. We show how significant constraints can be placed on the parameter space, not only from direct dark matter searches or LHC data but also from theoretical considerations like scattering unitarity or stability of the potential, and discuss some novel features of the allowed parameter space.

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