arXiv subjects

Ipsita Saha

Publications and source records attributed to Ipsita Saha.

At least 19 recordsLinked to original sources

arXiv2026

Soft Symmetry Breaking as a Nonstandard Source of Mass: Phenomenological Insights from the Two-Higgs-Doublet Model

The soft-breaking parameter, $m_{12}^2$, frequently appearing in the 2HDM scalar potential is much more remarkable than being just a nonstandard parameter that helps make the BSM scalars super heavy. In fact, as we show through explicit calculations, it should be treated as the direct but concise embodiment of new non-electroweak spontaneous symmetry breaking effects at very high energy scales, wherein lies its quiddities. Consequently, it is argued that $m_{12}^2$ and the electroweak VEV serve as two distinct sources for the nonstandard scalar masses, which are completely unrelated to each other. Such distinctions allow us to define parameters that conveniently capture the fraction of the nonstandard scalar masses derived from the electroweak VEV. Finally, we demonstrate that constraints can already be placed on such fractions from the current measurements of the diphoton signal strength and from direct searches of new nonstandard scalar resonances in the diphoton channel.

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arXiv2025

Consistent Excesses in the LHC Electroweak SUSY Searches: GUT-based Singlino/Higgsino Interpretation in the NMSSM

The search for supersymmetric models remains one of the main items on the BSM search program at the LHC, with EW SUSY partners still allowed with masses as low as a few hundred GeV. Over the last years, searches for the "golden channel", $pp \to \tildeχ^0_2 \tildeχ^{\pm}_1 \to \tildeχ^0_1 Z^{(*)} \tildeχ^0_1 W^{\pm (*)}$ show consistent excesses between ATLAS and CMS in the 2~soft-lepton and 3~soft-lepton plus missing-$E_T$ searches, assuming $m_{\tildeχ^0_2} \approx m_{\tildeχ^{\pm}_1} \gtrsim 200$ GeV and $Δm_{21} := m_{\tildeχ^0_2} - m_{\tildeχ^0_1} \approx 20$ GeV. We interpret these excesses in the framework of the Next-to-Minimal Supersymmetric Standard Model. We assume a singlino dominated lightest neutralino as a Dark Matter (DM) candidate. The second and third lightest neutralinos are higgsino like, with the higgsino mixing parameter $μ$ being smaller than the soft SUSY-breaking bino and wino masses, $M_1$ and $M_2$. We furthermore assume the approximate GUT relations $M_1 \sim M_2/2 \sim M_3/6$, with the implication for our scenario of a gluino mass $m_{\tilde{g}} \sim M_3 \gtrsim 3$ TeV. Scalar masses are assumed to heavy and do not play a role in our analysis. We find that this scenario is in agreement with all relevant experimental constraints, comprising the LHC searches for SUSY particles and additional Higgs bosons, the LHC Higgs-boson rate measurements, the DM direct detection limits and the upper limit on the DM relic density. We demonstrate that this scenario gives an excellent description of the observed excesses in the search for 2~and 3~soft-leptons plus \ETmiss, with $m_{\tildeχ^0_2} \sim m_{\tildeχ^0_3} \sim m_{\tildeχ^{\pm}_1}$ and $Δm_{21} \sim 20$ GeV. This constitutes the first explanation of the soft-lepton excesses in a model with GUT relations among the soft SUSY-breaking parameters.

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arXiv2024

$(g-2)_μ$ and Stau coannihilation : Dark Matter and Collider Analysis

Slepton coannihilation is one of the most promising scenarios that can bring the predicted Dark Matter (DM) abundance in the the Minimal Supersymmetric Standard Model (MSSM) into agreement with the experimental observation. In this scenario, the lightest supersymmetric particle (LSP), usually assumed to be the lightest neutralino, can serve as a Dark Matter (DM) candidate while the sleptons as the next-to-LSPs (NLSPs) lie close in mass. In our previous studies analyzing the electroweak (EW) sector of MSSM, a degeneracy between the three generations of sleptons was assumed for the sake of simplicity. In case of slepton coannihilation this directly links the smuons involved in the explanation for $(g-2)_μ$ to the coannihilating NLSPs required to explain the DM content of the universe. On the other hand, in well-motivated top-down models such degeneracy does not hold, and often the lighter stau turns out to be the NLSP at the EW scale, with the smuons (and selectrons) somewhat heavier. In this paper we analyze a non-universal slepton mass scenario at the EW scale where the first two generations of sleptons are taken to be mass-degenerate and heavier than the staus, enforcing stau coannihilation. We analyze the parameter space of the MSSM in the light of a variety of experimental data namely, the DM relic density and direct detection (DD) limits, LHC data and especially, the discrepancy between the experimental result for $(g-2)_μ$, and its Standard Model (SM) prediction. We find an upper limit on the LSP and NLSP masses of about ~ 550 GeV. In contrast to the scenario with full degeneracy among the three families of sleptons, the upper limit on the light smuon/selectron mass moves up by ~ 200 GeV. We analyze the DD prospects as well as the physics potential of the HL-LHC and a future high-energy $e^+ e^-$ collider to investigate this scenario further.

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arXiv2024

New physics interpretations for nonstandard values of $h\to Zγ$

Current measurement of the $h\to Zγ$ signal strength invite us to speculate about possible new physics interactions that exclusively affect $μ_{Zγ}$ without altering the other signal strengths. Additional consideration of tree-unitarity enables us to correlate the nonstandard values of $μ_{Zγ}$ with an upper limit on the scale of new physics. We find that even when $μ_{Zγ}$ deviates from the SM value by only $20\%$, the scale of new physics should be well within the reach of the LHC.

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arXiv2024

Consistent Excesses in the Search for $\tilde χ_2^{\rm 0} \tilde χ_1^{\rm \pm}$ : Wino/bino vs. Higgsino Dark Matter

The quest for supersymmetric (SUSY) particles is among the main search channels currently pursued at the LHC. Particularly, electroweak (EW) particles with masses as low as a few hundred GeV are still viable. Recent searches for the ``golden channel'', $pp \to \tilde χ_2^{\rm 0} \tilde χ_1^{\rm \pm} \to \tilde χ_1^{\rm 0} Z^{(*)} \, \tilde χ_1^{\rm 0} W^{\pm (*)}$ show consistent excesses between ATLAS and CMS in the 2~lepton, 3-lepton and mono-jet searches, assuming $m_{\tilde χ_2^{\rm 0}} \approx m_{\tilde χ_1^{\rm \pm}} \gtrsim 200$ GeV and $Δm := m_{\tilde χ_2^{\rm 0}} - m_{\tilde χ_1^{\rm 0}} \approx 20$ GeV. This mass configuration arises naturally in SUSY scenarios with wino/bino Dark Matter (DM) or higgsino DM. In these scenarios the lightest supersymmetric particle (LSP), assumed to be the lightest neutralino, as a DM candidate, is in good agreement with the observed limits on the DM content of the universe, as well as with negative results from Direct Detection (DD) experiments. We analyze these two scenarios with respect to the observed excesses, taking into account all relevant experimental constraints. We show that in particular wino/bino DM with different signs of the $SU(2)$ and $U(1)$ soft SUSY-breaking parameters can describe well the experimental excesses, while being in agreement with all other constraints.

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arXiv2024

Sign of the $hZZ$ coupling and implication for new physics

The magnitudes of the couplings of the scalar resonance at 125 GeV with the SM particles are found to be consistent with those of the SM Higgs boson. However, the signs are not experimentally determined in most of the cases, a prime example being that with the $Z$-boson pair. In other words, $κ_Z^h$, the ratio of the couplings of the actual 125 GeV resonance with $ZZ$ and that of the SM Higgs boson with the same, is consistent with both $+1$ and $-1$, the latter being the `wrong-sign'. We argue that the wrong-sign $hZZ$ coupling will necessitate the intervention of new physics below $\mathcal{O}\left(620\right)$ GeV to safeguard the underlying theory from unitarity violation. The strength of the new nonstandard couplings can be derived from the unitarity sum rules, which are comparable to the SM-Higgs couplings in magnitude. Thus the strong limits from the direct searches at the LHC can help us rule out the existence of such nonstandard particles with unusually large couplings thereby disfavoring the possibility of a wrong-sign $hZZ$ coupling.

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arXiv2023

New physics implications of VBF searches exemplified through the Georgi-Machacek model

LHC searches for nonstandard scalars in vector boson fusion (VBF) production processes can be particularly efficient in probing scalars belonging to triplet or higher multiplet representations of the Standard Model $SU(2)_L$ gauge group. They can be especially relevant for models where the additional scalars do not have any tree-level couplings to the Standard Model fermions, rendering VBF as their primary production mode at the LHC. In this work, we employ the latest LHC data from VBF resonance searches to constrain the properties of nonstandard scalars, taking the Georgi-Machacek model as a prototypical example. We take into account the theoretical constraints on the potential from unitarity and boundedness-from-below as well as indirect constraints coming from the signal strength measurements of the 125 GeV Higgs boson at the LHC. To facilitate the phenomenological analysis we advocate a convenient reparametrization of the trilinear couplings in the scalar potential. We derive simple correlations among the model parameters corresponding to the decoupling limit of the model. We explicitly demonstrate how a combination of theoretical and phenomenological constraints can push the GM model towards the decoupling limit. Our analysis suggests that the VBF searches can provide key insights into the composition of the electroweak vacuum expectation value.

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arXiv2023

Democratic three Higgs-doublet models: the custodial limit and wrong-sign Yukawa

We study two novel aspects of democratic 3HDMs -- the custodial limit and the possibility of wrong-sign Yukawa couplings. In the custodial limit, the democratic 3HDMs can easily negotiate the constraints from the electroweak $T$-parameter. We also uncover the possibility of having wrong-sign Yukawa couplings in democratic 3HDMs, as in the case of 2HDMs. We show that a democratic 3HDM encompasses all the wrong-sign possibilities entertained by 2HDMs, and has considerably more leeway in the wrong-sign limit as compared to the 2HDM case. Our study underscores the importance of reporting analysis in the kappa-formalism without any implicit assumptions on the signs of the kappas.

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arXiv2022

SUSY Dark Matter Direct Detection Prospects based on $(g-2)_μ$

An electroweak (EW) sector of the Minimal Supersymmetric Standard Model (MSSM) with masses of a few hundred GeV can account for variety of experimental data, assuming the lightest neutralino to be the lightest supersymmetric (SUSY) particle: the non-observation at the LHC searches owing to their small production cross sections, the results for the (upper limit of the) Dark Matter (DM) relic abundance and the DM Direct Detection (DD) limits. Such a light EW sector can in particular explain the reinforced $4.2\,σ$ discrepancy between the experimental result for $(g-2)_μ$, and its Standard Model (SM) prediction. Using the improved limits on $(g-2)_μ$, we review the predictions for the future prospects of the DD experiments. This analysis is performed for several different realizations of DM in the MSSM: bino, bino/wino, wino and higgsino DM. We find that higgsino, wino and one type of bino scenario can be covered by future DD experiments. Mixed bino/wino and another type of bino DM can reach DD cross sections below the neutrino floor. In these cases future collider experiments must cover the remaining parameter space.

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arXiv2021

$(g-2)_μ$ and SUSY Dark Matter: Direct Detection and Collider Search Complementarity

The electroweak (EW) sector of the Minimal Supersymmetric Standard Model (MSSM) can account for variety of experimental data. The EW particles with masses of a few hundred GeV evade the LHC searches owing to their small production cross sections. Such a light EW sector can in particular explain the reinforced $4.2\,σ$ discrepancy between the experimental result for the anomalous magnetic moment of the muon, \gmin2, and its Standard Model (SM) prediction. The lightest supersymmetric particle (LSP), assumed to be the lightest neutralino, $\tildeχ_1^0$, as a Dark Matter (DM) candidate is furthermore in agreement with the observed limits on the DM content of the universe. Here the Next-to LSP (NLSP) serves as a coannihilation partner and is naturally close in mass to the LSP. Such scenarios are also to a large extent in agreement with negative results from Direct Detection (DD) experiments. The DM relic density can fully be explained by a nearly pure bino or a mixed bino/wino LSP. Relatively light wino and higgsino DM, on the other hand, remains easily below the DM relic density upper bound. Using the improved limits on $(g-2)_μ$, we explore the mass ranges of the LSP and the NLSP in their correlation with the DM relic density for bino, bino/wino, wino and higgsino DM. In particular analyze the sensitivity of future DM DD experiments to these DM scenarios. We find that higgsino, wino and one type of bino scenario can be covered by future DD experiments. Mixed bino/wino and another type of bino DM can reach DD cross sections below the neutrino floor. In these cases we analyze the complementarity with the (HL-)LHC and future $e^+e^-$ linear colliders. We find that while the prospects for the HL-LHC are interesting, but not conclusive, an $e^+e^-$ collider with $\sqrt{s} \le 1$ TeV can cover effectively all points of the MSSM that may be missed by DD experiments.

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arXiv2021

SUSY in the light of the new "MUON G-2" Result

The recently published result from the Fermilab "MUON G-2" experiment has confirmed the persistent 3-4 $σ$ discrepancy between the experimental result from BNL for the anomalous magnetic moment of the muon, $(g-2)_μ$ , and its Standard Model (SM) prediction. The combination of the two measurements yields a deviation of 4.2 $σ$ from the SM value. Here, we review the parameter space of the electroweak (EW) sector of the Minimal Supersymmetric Standard Model (MSSM), that can accommodate the anomaly while being in full agreement with other experimental data, particularly the direct searches for EW particles at the LHC and dark matter (DM) relic density and direct detection constraints. We find that the combined constraints set an upper limit of ~ 600 GeV for the LSP and NLSP masses establishing clear targets for the future collider searches.

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arXiv2021

Prospects of light charged scalars in a three Higgs doublet model with $Z_3$ symmetry

The stringent constraints from the direct searches for exotic scalars at the LHC as well as indirect bounds from flavor physics measurements have imposed severe restrictions on the parameter space of new physics models featuring extended Higgs sectors. In the Type-II 2HDM, this implies a lower bound on the charged Higgs masses of $\cal O$(600 GeV). In this work we analyze the phenomenology of a Z3HDM in the alignment limit focusing on the impact of flavor physics constraints on its parameter space. We show that the couplings of the two charged Higgs bosons in this model feature an additional suppression factor compared to Type-II 2HDM. This gives rise to a significant relaxation of the flavor physics constraints in this model, allowing the charged Higgs masses to be as low as $\cal O$(200 GeV). We also consider the constraints coming from precision electroweak observables and the observed diphoton decay rate of the 125 GeV Higgs boson at the LHC. The bounds coming from the direct searches of nonstandard Higgs bosons at the LHC, particularly those from resonance searches in the ditau channel, prove to be very effective in constraining this scenario further.

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arXiv2021

Leptophilic fermion WIMP ~ Role of future lepton colliders

The leptophilic weakly interacting massive particle (WIMP) is realized in a minimal renormalizable model scenario where scalar mediators with lepton number establish the WIMP interaction with the standard model (SM) leptons. We perform a comprehensive analysis for such a WIMP scenario for two distinct cases with an SU(2) doublet or singlet mediator considering all the relevant theoretical, cosmological and experimental constraints at present. We show that the mono-photon search at near-future lepton collider experiments (ILC, FCC-ee, CEPC, etc.) can play a significant role to probe the yet unexplored parameter range allowed by the WIMP relic density constraint. This will complement the search prospect at the near-future hadron collider experiment (HL-LHC). Furthermore, we discuss the combined model scenario including both the doublet and singlet mediator. The combined model is capable of explaining the long-standing muon (g-2) anomaly which is an additional advantage. We demonstrate that the allowed region for anomalous muon (g-2) explanation, which has been updated very recently at Fermi National Accelerator Laboratory, can also be probed at the future colliders which will thus be a simultaneous authentication of the model scenario.

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arXiv2021

Improved $(g-2)_μ$ Measurements and Supersymmetry

The electroweak (EW) sector of the Minimal Supersymmetric Standard Model (MSSM) can account for a variety of experimental data. The lighest supersymmetric particle (LSP), which we take as the lightest neutralino, $\tilde χ_1^0$, can account for the observed Dark Matter (DM) content of the universe via coannihilation with the next-to-LSP (NLSP), while being in agreement with negative results from Direct Detection (DD) experiments. Owing to relatively small production cross-sections a comparably light EW sector of the MSSM is also in agreement with the unsuccessful searches at the LHC. Most importantly, the EW sector of the MSSM can account for the persistent $3-4\,σ$ discrepancy between the experimental result for the anomalous magnetic moment of the muon, $(g-2)_μ$, and its Standard Model (SM) prediction. Under the assumption that the $\tilde χ_1^0$ provides the full DM relic abundance we first analyze which mass ranges of neutralinos, charginos and scalar leptons are in agreement with all experimental data, including relevant LHC searches. We find an upper limit of $\sim 600$ GeV for the LSP and NLSP masses. In a second step we assume that the new result of the Run 1 of the ``MUON G-2'' collaboration at Fermilab yields a precision comparable to the existing experimental result with the same central value. We analyze the potential impact of the combination of the Run 1 data with the existing $(g-2)_μ$ data on the allowed MSSM parameter space. We find that in this case the upper limits on the LSP and NLSP masses are substantially reduced by roughly $100$ GeV. This would yield improved upper limits on these masses of $\sim 500$ GeV. In this way, a clear target could be set for future LHC EW searches, as well as for future high-energy $e^+e^-$ colliders, such as the ILC or CLIC.

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arXiv2021

Improved $(g-2)_μ$ Measurements and Supersymmetry : Implications for $e^+e^-$ colliders

The persistent 3-4$σ$ discrepancy between the experimental result from BNL for the anomalous magnetic moment of the muon and its Standard Model (SM) prediction, was confirmed recently by the "MUON G-2" result from Fermilab. The combination of the two measurements yields a deviation of 4.2$σ$ from the SM value. Here, we review an analysis of the parameter space of the electroweak (EW) sector of the Minimal Supersymmetric Standard Model (MSSM), which can provide a suitable explanation of the anomaly while being in full agreement with other latest experimental data like the direct searches for EW particles at the LHC and dark matter (DM) relic density and direct detection constraints. Taking the lightest supersymmetric particle (LSP) (the lightest neutralino in our case) to be the DM candidate, we discuss the case of a mixed bino/wino LSP, which can account for the full DM relic density of the universe and that of wino and higgsino DM, where we take the relic density only as an upper bound. We observe that an upper limit of ~ 600 GeV can be obtained for the LSP and next-to (N)LSP masses establishing clear search targets for the future HL-LHC EW searches, but in particular for future high-energy $e^+e^-$ colliders, such as the ILC or CLIC.

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arXiv2021

The new "MUON G-2" Result and Supersymmetry

The electroweak (EW) sector of the Minimal Supersymmetric Standard Model (MSSM), with the lightest neutralino as Dark Matter (DM) candidate, can account for a variety of experimental data. This includes the DM content of the universe, DM direct detection limits, EW SUSY searches at the LHC and in particular the so far persistent $3-4\,σ$ discrepancy between the experimental result for the anomalous magnetic moment of the muon, $(g-2)_μ$, and its Standard Model (SM) prediction. The recently published ``MUON G-2'' result is within $0.8\,σ$ in agreement with the older BNL result on $(g-2)_μ$. The combination of the two results was given as $a_μ^{\rm exp} = (11 659206.1 \pm 4.1c) \times 10^{-10}$, yielding a new deviation from the SM prediction of $Δa_μ= (25.1 \pm 5.9) \times 10^{-10}$, corresponding to $4.2\,σ$. Using this improved bound we update the results presented in [1] and set new upper limits on the allowed parameters space of the EW sector of the MSSM. We find that with the new $(g-2)_μ$ result the upper limits on the (next-to-) lightest SUSY particle are in the same ballpark as previously, yielding updated upper limits on these masses of $\sim 600$ GeV. In this way, a clear target is confirmed for future (HL-)LHC EW searches, as well as for future high-energy $e^+e^-$ colliders, such as the ILC or CLIC.

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arXiv2021

Improved $(g-2)_μ$ Measurements and Wino/Higgsino Dark Matter

The electroweak (EW) sector of the Minimal Supersymmetric Standard Model (MSSM) can account for a variety of experimental data. In particular, it can explain the persistent 3-4 sigma discrepancy between the experimental result for the anomalous magnetic moment of the muon and its Standard Model (SM) prediction. The lightest supersymmetric particle (LSP), which we take as the lightest neutralino, can furthermore account for the observed Dark Matter (DM) content of the universe via coannihilation with the next-to-LSP (NLSP), while being in agreement with negative results from Direct Detection (DD) experiments. Concerning the unsuccessful searches for EW superparticles at the LHC, owing to relatively small production cross-sections, a comparably light EW sector of the MSSM is in full agreement with the experimental data. The DM relic density can fully be explained by a mixed bino/wino LSP. Here we take the relic density as an upper bound, which opens up the possibility of wino and higgsino DM. We first analyze which mass ranges of neutralinos, charginos and scalar leptons are in agreement with all experimental data, including relevant LHC searches. We find roughly an upper limit of ~ 600 GeV for the LSP and NLSP masses. In a second step we assume that the new result of the Run 1 of the 'MUON G-2' collaboration at Fermilab yields a precision comparable to the existing experimental result with the same central value. We analyze the potential impact of the combination of the Run 1 data with the existing muon g-2 data on the allowed MSSM parameter space. We find that in this case the upper limits on the LSP and NLSP masses are substantially reduced by roughly 100 GeV. We interpret these upper bounds in view of future HL-LHC EW searches as well as future high-energy electron-positron colliders, such as the ILC or CLIC.

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arXiv2021

Muon Anomalous Magnetic Moment in Two Higgs Doublet Models with Vector-Like Leptons

We show that inclusion of a single generation of vector-like leptons in the Two-Higgs Doublet Models significantly enlarges the allowed parameter space consistent with the muon anomalous magnetic moment, as well as with other theoretical and experimental constraints. While previously $(g -2)_μ$ could only be resolved in Type-X scenario by requiring a light pseudoscalar Higgs boson and large $\tan β$, contributions of vector-like leptons via two-loop Barr Zee diagrams broaden the allowed parameter space, allowing $\tan β$ as low as 10 and pseudoscalar masses as large as $\cal{O}$(1 TeV) while fulfilling the stringent constraints from precision and flavor observable. Similar results are obtained for Type-II scenarios, but there the parameter space is more restricted by flavor observables.

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