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Tanmoy Modak

Publications and source records attributed to Tanmoy Modak.

At least 37 records · Page 2Linked to original sources

Echoes of 2HDM inflation at the collider experiments

We study the correlation between the constraints on general two Higgs doublet model from Higgs inflation and from collider experiments. The parameter space receives meaningful constraints from direct searches at the Large Hadron Collider and from flavor physics if $m_H$, $m_A$, and $m_{H^\pm}$ are in the sub-TeV range, where $H$, $A$, and $H^\pm$ are the CP even, CP odd, and charged Higgs bosons, respectively. We find that in the parameter region favored by the Higgs inflation, $H$, $A$, and $H^\pm$ are nearly degenerate in mass.We show that such near degeneracy can be probed directly in the upcoming runs of the Large Hadron Collider, while the future lepton colliders such as the International Linear Collider and the Future Circular Collider would provide complementary probes.

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A Final Word on FCNC-Baryogenesis from Two Higgs Doublets

Electroweak baryogenesis in a two-Higgs doublet model is a well-motivated and testable scenario for physics beyond the Standard Model. An attractive way of providing $CP$ violation is through flavor-changing Higgs couplings, where the top-charm coupling is hardly constrained. This minimal scenario can be tested by searching for heavy charged and neutral Higgs bosons at the LHC. While the charged Higgs signature requires a dedicated analysis, the neutral Higgs signature will be covered by a general search for same-sign top pairs. Together, they provide a conclusive test of this kind of baryogenesis.

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Prospect and implications of $cg\to bH^+\to b A W^+$ production at the LHC

We study the prospect for discovering the $cg\to bH^+\to b A W^+$ process at the LHC. Induced by the top-flavor changing neutral Higgs coupling $ρ_{tc}$, the process may emerge if $m_{H^+} > m_A + m_{W^+}$, where $H^+$ and $A$ are charged and $CP$-odd Higgs bosons in the general two Higgs Doublet Model (g2HDM). We show that the $cg\to bH^+\to b A W^+$ process can be discovered at LHC Run 3, while the full Run 2 data at hand can constrain the parameter space significantly by searching for the same-sign dilepton final state. The process has unique implications on the hint of $gg\to A \to t \bar t$ excess at $m_A\approx 400$ GeV reported by CMS. When combined with other existing constraints, the $cg\to bH^+\to b A W^+$ process can essentially rule out the g2HDM explanation of such an excess.

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Probing Top Changing Neutral Higgs Couplings at Colliders

The $h(125)$ boson, discovered only in 2012, is lower than the top quark in mass, hence $t \to ch$ search commenced immediately thereafter, with current limits at the per mille level and improving. As the $t \to ch$ rate vanishes with the $h$-$H$ mixing angle $\cosγ\to 0$, we briefly review the collider probes of the top changing $tcH/tcA$ coupling $ρ_{tc}$ of the exotic $CP$-even/odd Higgs bosons $H/A$. Together with an extra top conserving $ttH/ttA$ coupling $ρ_{tt}$, one has an enhanced $cbH^+$ coupling alongside the familiar $tbH^+$ coupling, where $H^+$ is the charged Higgs boson. The main processes we advocate are $cg \to tH/A \to tt\bar c,\; tt\bar t$ (same-sign top and triple-top), and $cg \to bH^+ \to bt\bar b$. We also discuss some related processes such as $cg \to thh$, $tZH$ that depend on $\cosγ$ being nonzero, comment briefly on $gg \to H/A \to t\bar t, t\bar c$ resonant production, and touch upon the $ρ_{tu}$ coupling.

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Sub-TeV $H^+$ Boson Production as Probe of Extra Top Yukawa Couplings

We suggest searching for the charged Higgs boson at the Large Hadron Collider (LHC) via $cg \to b H^+ \to b t \bar b$. In the general two Higgs Doublet Model, extra top Yukawa couplings $ρ_{tc}$ and $ρ_{tt}$ can drive the disappearance of antimatter from the Universe, while $\bar cbH^+$ and $\bar tbH^+$ couple with strength $ρ_{tc}V_{tb}$ and $ρ_{tt}V_{tb}$, respectively. For $ρ_{tc},\, ρ_{tt} \sim 0.5$ and $m_{H^+} \sim 300$--500 GeV, evidence could emerge from LHC Run 2 data at hand, and discovery by adding Run 3 data in the near future.

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Probing Electroweak Baryogenesis induced by extra bottom Yukawa coupling via EDMs and collider signatures

We study the prospect of probing electroweak baryogenesis driven by an extra bottom Yukawa coupling $ρ_{bb}$ in a general two Higgs doublet model via electric dipole moment (EDM) measurements and at the collider experiments. The parameter space receives meaningful constraints from 125 GeV Higgs $h$ boson signal strength measurements as well as several heavy Higgs boson searches at the Large Hadron Collider (LHC). In addition, we show that the asymmetry of the CP asymmetry of inclusive $B\to X_s γ$ decay would provide complementary probe. A discovery is possible at the LHC via $bg\to bA \to b Z h$ process if $|ρ_{bb}|\sim 0.15$ and $250~\mbox{GeV}\lesssim m_A \lesssim 350$ GeV, where $A$ is CP odd scalar. For $m_A> 2 m_t$ threshold, where $m_t$ is the top quark mass, one may also discover $bg\to bA \to b t \bar t$ at the high luminosity LHC run if an extra top Yukawa coupling $|ρ_{tt}|\sim0.5$, though it may suffer from systematic uncertainties. For completeness we study $gg\to t \bar t A \to t \bar t b \bar b $ but find it not promising.

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Constraining $t \to u$ flavor changing neutral Higgs coupling at the LHC

We study the constraints on $t\to u$ flavor changing neutral Higgs (FCNH) coupling, and how it may be explored further at the Large Hadron Collider (LHC). In the general two Higgs doublet model, such transitions can be induced by a nonzero $ρ_{tu}$ Yukawa coupling. We show that such couplings can be constrained by existing searches at the LHC for $m_H$, $m_A$ and, $m_{H^+}$ in the sub-TeV range, where $H$, $A$ and $H^+$ are the exotic $CP$-even, $CP$-odd and charged scalars. We find that a dedicated $ug\to t H/tA \to t t \bar u$ search can probe the available parameter space of $ρ_{tu}$ down to a few percent level for $200\,\mbox{GeV} \lesssim m_H,\,m_A \lesssim 600$ GeV, with discovery possible at high luminosity. Effects of how other extra top Yukawa couplings, such as $ρ_{tc}$ and $ρ_{tt}$, dilute the sensitivity of the $ρ_{tu}$ probe are discussed.

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Testing triplet fermions at the electron-positron and electron-proton colliders using fat jet signatures

The addition of $SU(2)_L$ triplet fermions of zero hypercharge with the Standard Model (SM) helps to explain the origin of the neutrino mass by the so-called seesaw mechanism. Such a scenario is commonly know as the type-III seesaw model. After the electroweak symmetry breaking the mixings between the light and heavy mass eigenstates of the neutral leptons are developed which play important roles in the study of the charged and neutral multiplets of the triplet fermions at the colliders. In this article we study such interactions to produce these multiplets of the triplet fermion at the electron-positron and electron-proton colliders at different center of mass energies. We focus on the heavy triplets, for example, having mass in the TeV scale so that their decay products including the SM the gauge bosons or Higgs boson can be sufficiently boosted, leading to a fat jet. Hence we probe the mixing between light-heavy mass eigenstates of the neutrinos and compare the results with the bounds obtained by the electroweak precision study.

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The $tZH$ and $tZh$ production in 2HDM: Prospects for discovery at the LHC

We study the discovery potential of the $cg \to tA\to tZH$ process at the LHC, where $A$ and $H$ are CP-odd and even exotic scalars, respectively. The context is the general Two Higgs Doublet Model, where $cg \to tA$ is induced by the flavor changing neutral Higgs coupling $ρ_{tc}$. We find that the process $cg \to tA\to tZH$ can be discovered for $m_A \sim 400$ GeV, but would likely require high luminosity running of the LHC. Such a discovery would shed light on the mechanism behind the observed Baryon Asymmetry of the Universe. We also study $cg \to tA\to tZh$, where $h$ is the observed 125 GeV scalar, but find it out of reach at the LHC.

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Scalar leptoquark effects on $B \to μ\barν$ decay

Purely leptonic $B$ meson decays provide unique probes for physics Beyond the Standard Model. We study the impact of a scalar leptoquark, $S_1$, on $B \to μ\barν$ decay. We find that, for $m_{S_1}\sim 1$ TeV, the $S_1$ leptoquark can modify the $B \to μ\barν$ rate significantly. Such a leptoquark can in prinicple also alter the $B \to τ\barν$ rate. However, current searches from LHC and low energy physics provide some constraints on the parameter space.

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Enhanced $B \to μ\barν$ Decay at Tree Level as Probe of Extra Yukawa Couplings

With no New Physics seen at the LHC, a second Higgs doublet remains attractive and plausible. The ratio ${\cal R}_B^{μ/τ} = {\cal B}(B \to μ\barν)/{\cal B}(B \to τ\barν)$ is predicted at 0.0045 in both the Standard Model and the type II two Higgs doublet model, but it can differ if extra Yukawa couplings exist in Nature, which we deem an experimental issue. Considering recent Belle update on $B \to μ\barν$, we show that in the general two Higgs doublet model, the ratio could be up by a factor of two, which can be probed by the Belle~II experiment with just a few ab$^{-1}$.

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Implications of Four-Top and Top-Pair Studies on Triple-Top Production

Multi-top quark production is a staple program at the LHC. Single-top and $t\bar t$ productions are studied extensively, while current efforts are zooming in on four-top search, where the Standard Model (SM) cross section is at ${\cal O}(10)$ fb. In contrast, only at the fb level in SM, triple-top production has not been targeted for study so far. But such a small cross section makes it a unique probe for New Physics. Without the usual discrete $Z_2$ symmetry, the general two Higgs doublet model (g2HDM) can naturally raise the triple-top production to pb level. We illustrate how certain signal regions of four-top search can be utilized to constrain triple-top production, but urge a dedicated search. As an aside, we note that the CMS study at 13 TeV of scalar $t\bar t$ resonance interfering with QCD production background indicate some activity at 400 GeV. We comment that this could be explained in principle in g2HDM via the extra top Yukawa coupling.

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Probing an additional bottom Yukawa coupling via $bg\to b A \to b Z H$ signature

The recent discovery of the bottom quark Yukawa coupling ($hbb$) of the 125 GeV scalar motivates one to search for extra bottom Yukawa coupling that may exist in the nature. The two Higgs doublet model without a discrete $Z_2$ symmetry allows the possibility of additional bottom Yukawa coupling $ρ_{bb}$. We show that $ρ_{bb}$ can be searched directly at the LHC via $bg\to b A \to b Z H$ and $gg \to b \bar b A \to b \bar b Z H$ processes, where $A$ and $H$ are the CP-odd and CP-even scalars respectively. We find that the $bg\to b A \to b Z H$ process could be discovered with $\sim300$ fb$^{-1}$ integrated luminosity if $ m_A \sim 300$ GeV, while the latter process may emerge in the high luminosity LHC (HL-LHC) data. A discovery might touch upon the parameter space required for the electroweak baryogenesis.

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Electroweak baryogenesis via bottom transport

We consider a scenario in which an extra bottom Yukawa coupling can drive electroweak baryogenesis in the general two-Higgs doublet model. It is found that the new bottom Yukawa coupling with $\mathcal{O}(0.1)$ in magnitude can generate the sufficient baryon asymmetry without conflicting existing data. We point out that future measurements of the bottom Yukawa coupling at High-Luminosity Large Hadron Collider and International Linear Collider, together with the CP asymmetry of $B\to X_sγ$ at SuperKEKB provide exquisite probes for this scenario.

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Top-Assisted Di-Higgs boson Production Motivated by Baryogenesis

We study top-assisted di-Higgs production via $cg \to tH \to thh$, where $h$ is the 125 GeV scalar boson, and $H$ is the $CP$-even heavy Higgs. The context is the two Higgs doublet model without a $Z_2$ symmetry, where the extra Yukawa coupling $ρ_{tc}$ generates $tH$ production, with the extra top Yukawa $ρ_{tt} \simeq 0$ to avoid $gg \to H$ constraints. We find that discovery is possible for $m_H$ around 300 GeV or so at the LHC, but would need finite $h$-$H$ mixing angle $\cosγ$ to allow for finite $λ_{Hhh}$ coupling, and $ρ_{tc}$ also needs to be not too small. A sizable $ρ_{tc}$ could drive electroweak baryogenesis, which further motivates the search.

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Probing for Extra Top Yukawa Couplings in Light of $t\bar th(125)$ Observation

The observation of $t\bar th(125)$ production at the Large Hadron Collider (LHC) is the first direct measurement of the top Yukawa coupling. It opens the window on an extra top Yukawa coupling, $ρ_{tt}$, from a second Higgs doublet, without a $Z_2$ symmetry to forbid flavor changing neutral Higgs couplings. We show that $t\bar th$ and Higgs property measurements at the High Luminosity LHC can constrain the ${\rm Re}\,ρ_{tt}$--${\rm Im}\,ρ_{tt}$ parameter space that could drive electroweak baryogenesis, but the $Γ_h$ width measurement must be considerably improved beyond current projections.

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$U(1)_{B_3-3L_μ}$ gauge symmetry as a simple description of $b\to s$ anomalies

We present a simple $U(1)_{B_3-3L_μ}$ gauge Standard Model extension that can easily account for the anomalies in $R(K)$ and $R(K^*)$ reported by LHCb. The model is economical in its setup and particle content. Among the Standard Model fermions, only the third generation quark family and the second generation leptons transform non-trivially under the new $U(1)_{B_3-3L_μ}$ symmetry. This leads to lepton non-universality and flavor changing neutral currents involving the second and third quark families. We discuss the relevant experimental constraints and some implications.

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Constraining a Lighter Exotic Scalar via Same-sign Top

It was shown recently that, in two Higgs doublet models without $Z_2$ symmetry, extra Yukawa couplings such as $ρ_{tc}$, $ρ_{tt}$ can fuel enough $CP$ violation for electroweak baryogenesis (EWBG). We revisit an old proposal where a pseudoscalar $A^0$ has mass between $t\bar c$ and $t\bar t$ thresholds. With $ρ_{tt}$ small, it evades $gg \to A^0 \to h^0(125)Z$ constraints, where approximate alignment also helps. We find this scenario with relatively light $A^0$ is not yet ruled out, and $cg \to tA^0 \to tt\bar c$ can probe sizable $ρ_{tc}$ at the LHC, giving access to the second mechanism of EWBG provided by such models.

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