arXiv subjects

Ambresh Shivaji

Publications and source records attributed to Ambresh Shivaji.

At least 19 recordsLinked to original sources

arXiv2026

Constraining the Higgs potential using multi-Higgs production

The Higgs self-couplings remain only weakly constrained by current Large Hadron Collider (LHC) measurements, leaving ample room for physics beyond the Standard Model that could modify the structure of the Higgs potential. Multi-Higgs production processes provide a particularly sensitive probe of deviations in both the Higgs trilinear and quartic self-couplings. In this note, we summarize the current status of next-to-leading-order electroweak (EW) corrections to double-Higgs production computed within the Standard Model Effective Field Theory and Higgs Effective Field Theory frameworks, emphasizing how these calculations introduce sensitivity to the Higgs self-couplings beyond what is accessible at leading order. We discuss the key conceptual and technical differences between the two effective field theory approaches, including their treatment of higher-dimensional operators, renormalization procedures, and the structure of EW~two-loop amplitudes. Despite these differences, both approaches yield broadly consistent constraints, illustrating the complementarity of double- and triple-Higgs measurements. With the high-luminosity LHC and future high-energy colliders on the horizon, these developments and further advances provide an essential foundation for extracting increasingly precise information on the dynamics of EW symmetry breaking.

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arXiv2025

Two-loop form factors for Dark Matter annihilation to colored Standard Model particles

We investigate a UV-complete model in which the dark matter (DM) particle interacts with gluons through a colored scalar mediator. This framework provides a phenomenologically viable scenario testable at hadron colliders. While mono-jet signatures are relevant for collider searches, zero-jet processes correspond to complete annihilation of Standard Model (SM) particles into DM, contributing to the relic density. In this work, we study dark matter annihilation into SM colored particles, which in our model arises at leading order from loop-induced processes. We compute the relevant two-loop QCD amplitudes for both gluon and quark channels in dark matter production or annihilation. The amplitudes are decomposed into scalar form factors using the projector technique. Using integration-by-parts (IBP) identities, we obtain analytical expressions for the form factors in terms of master integrals. Ultraviolet divergences are removed via counterterm renormalization, yielding UV-finite results. These results would enable predictions for dark matter production or annihilation into SM colored particles at next-to-leading order (NLO) in QCD.

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arXiv2025

NLO QCD effects on angular observables in $e^-p \to e^-(\nu_e)Hj$ in presence of non-standard $HVV$ couplings

The single Higgs production in neutral-current (NC) and charged-current (CC) processes at an electron-proton ($ep$) collider is a useful channel to probe new physics effects in the Higgs coupling to vector boson ($HVV$). In this context, observables sensitive to non-standard couplings previously studied at leading order require improved theoretical precision through the inclusion of radiative corrections. In this work, we present a fully differential Higgs plus one jet production at next-to-leading-order (NLO) accuracy in QCD for both the NC and CC processes. For the proposed Large Hadron electron Collider (LHeC) configuration, with a 60~GeV electron beam and a 7~TeV proton beam, the total cross sections receive modest corrections with significantly reduced scale uncertainties. We find that in several kinematic distributions which are relevant to the analysis of $HVV$ couplings, the NLO K-factors are not flat. Within the Standard Model, the polar angle of the electron (for NC) and the azimuthal angular correlation (for both NC and CC processes) receive maximum corrections in the range of 8-10\% in certain bins. We also compute NLO QCD corrections in the presence of non-standard $HVV$ interactions. The corrections in the azimuthal angular correlations are similar to the standard model predictions. For the polar angle of the electron, the corrections are sensitive to the nature of the $HVV$ coupling.

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arXiv2025

Role of angular observables in probing non-standard $HZZ$ couplings at an electron-proton collider

In this study, we explore various lab-frame angular observables at Large Hadron-electron Collider (LHeC) to test their sensitivity on the most general structure of the Higgs ($H$) to neutral weak boson ($Z$) coupling ($HZZ$) via the process $e^- p \rightarrow e^- H j$ at the center of mass energy $\sqrt{s}~\approx$ 1.3 TeV. The most general Lorentz structure of the $HZZ$ coupling beyond the standard model is composed of two CP-even ($\lambda_{1Z}$ and $\lambda_{2Z}$) and one CP-odd (${\tilde \lambda_Z}$) components. In a previous study, we looked at the absolute value of azimuthal correlation ($|\Delta \phi|$) between the final state electron and the jet to derive constraints on the non-standard $HZZ$ couplings. This choice of observable is motivated by its potential to discriminate between CP-odd and CP-even couplings in the $e^- p \rightarrow \nu_e H j$ process. Since the process $e^- p \rightarrow e^- H j$ has an electron in the final state, one can construct more angular observables. In addition to $|\Delta \phi|$, we identify new angular observables: the sign-sensitive azimuthal correlation ($\Delta \phi$) and the polar angle of the final state electron ($\theta$), suitable for constraining non-standard $HZZ$ coupling. Our analysis shows that these new angles improve the constraints on $\lambda_{2Z}$ and ${\tilde \lambda}_Z$ in the range of 48-67\%. We also study the potential of the asymmetry in $\Delta \phi$ to constrain the parameters corresponding to the CP-odd coupling.

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arXiv2024

NLO QCD effects on angular observables in single Higgs production at electron-proton collider

Properties of the Higgs boson ($H$) at current and future particle colliders are crucial to explore new physics beyond the standard model. In particular, experimental and theoretical outlooks at future colliders drive interest in Higgs to gauge boson couplings. Single Higgs production via vector-boson fusion allows probing Higgs couplings with massive vector bosons ($V = W, Z$). We consider electron-proton (eP) collider to study these couplings due to the low background. In a recent study, we considered the most general anomalous Higgs-vector boson ($HVV$) couplings and explored the potential of eP collider in constraining the parameters of $HVV$ couplings. Our results were based on leading order predictions in perturbation theory. We include further Next to Leading Order (NLO) corrections of Quantum Chromodynamic (QCD) in Standard Model signal to make precise predictions. In this talk, I will present the effect of NLO QCD corrections on the standard model and anomalous $HVV$ couplings.

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arXiv2024

QCD corrections to the Golden decay channel of the Higgs boson

Future colliders aim to provide highly precise experimental measurements of the properties of the Higgs boson. In order to benefit from these precision machines, theoretical errors in the Higgs sector observables have to match at least the experimental uncertainties. The theoretical uncertainties in the Higgs sector observables can be reduced by including missing higher-order terms in their perturbative calculations. In this direction, we compute the mixed QCD-electroweak corrections at ${\mathcal O}(αα_s)$ to the Higgs decay into four charged leptons by considering the golden decay channel, $ H \to e^+e^-μ^+μ^-$. Due to color conservation, these corrections receive contributions only from the two-loop virtual diagrams. In the complex mass scheme, we find that the mixed QCD-electroweak corrections to the partial decay width, relative to the leading order predictions, are positive and about $0.27\%$ for $α_s(M_Z)$. Relative to the next-to-leading order electroweak corrections, the mixed QCD-electroweak corrections are found to be approximately $18\%$ for $α_s(M_Z)$. With respect to the leading order, we observe a flat effect of the mixed QCD-electroweak corrections on the invariant mass distribution of the lepton pairs with fixed QCD coupling. The $ϕ$ distribution, due to the mixed QCD-electroweak corrections, follows a $(1-\cos ϕ)$ dependence.

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arXiv2022

Master integrals for ${\cal O}(αα_s)$ corrections to $H \to ZZ^*$

We present analytic results for all the Feynman integrals relevant for ${\mathcal O}(αα_s)$ virtual corrections to $H \rightarrow ZZ^*$ decay. We use the method of differential equations to solve the master integrals while keeping the full dependence on the masses of all the particles including internal propagators. Due to the presence of four mass scales we encounter multiple square roots. We argue that all the occurring square roots can not be rationalized at the same time as a simultaneous rationalization brings us to integrals over $CY_3$ manifolds. Hence we rationalize only three square roots simultaneously and construct suitable ansätze to obtain dlog-forms containing the square root, after obtaining an epsilon-factorised form for the differential equations. We present the alphabet and the analytic form of all the boundary constants that appear in the solutions of the differential equations. The results for master integrals are expressed in terms of Chen's iterated integrals with dlog one-forms.

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arXiv2022

Probing non-standard $HVV (V=W, Z)$ couplings in single Higgs production at future electron-proton collider

The couplings of the Higgs boson ($H$) with massive gauge bosons of weak interaction ($V= W, Z$), can be probed in single Higgs boson production at the proposed future Large Hadron-Electron Collider (LHeC). In the collision of an electron with a proton, single Higgs production takes place via so-called charged-current ($e^-p \to ν_e H j$) and neutral-current ($e^-p \to e^-H j$) processes. We explore the potential of the azimuthal angle correlation between the forward jet and scattered neutrino or electron in probing the non-standard $HVV$ couplings at the collider center-of-mass energy of $\sqrt{s} \approx 1.3$~TeV. We choose the most general modifications (of $CP$-even and $CP$-odd nature) to these couplings due to new physics effects beyond the standard model. We derive exclusion limits on new physics parameters of $HVV$ couplings as a function of integrated luminosity at $95\%$ C.L. using the azimuthal angular correlations in charged- and neutral-current processes. We find that using 1000 $fb^{-1}$ data, the standard model-like new physics parameters in $HWW$ and $HZZ$ couplings can be constrained with accuracies of $4\%$ and $15\%$, respectively. The least constrained $CP$-even parameters of $HWW$ coupling can be as large as 0.04, while those of $HZZ$ coupling can have values around 0.31. Allowed values of $CP$-odd parameters in $HWW$ and $HZZ$ couplings are found to be around 0.14 and 0.34, respectively. We also study changes in the allowed values of non-trivial new physics parameters in the presence of other parameters.

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arXiv2021

Di-vector boson production in association with a Higgs boson at hadron colliders

We consider the production of a Higgs boson in association with two electroweak vector bosons at hadron colliders. In particular, we examine $γγH$, $γZH$, $ZZH$, and $W^{+}W^{-}H$ production at the LHC (14 TeV), HE-LHC (27 TeV), and FCC-hh (100 TeV) colliders. Our main focus is to estimate the gluon-gluon ($gg$) channel ($gg \to VV^\prime H$) contributions to $pp \to VV^\prime H~(V,V^\prime=γ,Z,W)$ and compare them with corresponding contributions arising from the quark-quark ($qq$) channel. Technically, the leading order $gg$ channel contribution to $pp \to VV^\prime H$ cross section is an NNLO correction in $α_s$. In the processes under consideration, we find that in the $gg$ channel, $W^{+}W^{-}H$ has the largest cross section. However, relative contribution of the $gg$ channel is more important for the $pp \to ZZH$ production. At the FCC-hh, $gg \to ZZH$ contribution is comparable with the NLO QCD correction to $qq \to ZZH$. We also compute the cross sections when $W$ and $Z$-bosons are polarized. In the production of $W^{+}W^{-}H$ and $ZZH$, we find that the $gg$ channel contributes more significantly when the vector bosons are longitudinally polarized. By examining such events, one can increase the fraction of the $gg$ channel contribution to these processes. Further, we have studied beyond-the-standard-model effects in the $κ$-framework. We find that the $gg$ channel processes $ZZH$ and $WWH$ have very mild dependence on $κ_λ$, but strong dependence on $κ_t$ and $κ_V$. The $qq$ channel processes mainly depend on $κ_V$. Dependence of the $gg$ channel contribution on $κ_V$ is stronger than that of the $qq$ channel contribution. Therefore focusing on events with longitudinally polarized $W$ and $Z$-bosons, one can find stronger dependence on $κ_V$ that can help us measure this parameter.

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arXiv2018

Direct measurement of the Higgs self-coupling in $e^+e^- \to ZH$

A new method to measure the trilinear Higgs self-coupling $λ_3^{}$ in a single Higgs production process is proposed. Time-reversal-odd (T-odd) asymmetries in the process $e^+_{}e^-_{} \to ZH$, $Z \to f\bar{f}$ are computed from the absorptive part of the electroweak one-loop amplitude. Since the T-odd asymmetries measure the tree-level $t$-channel $ZH \to ZH$ scattering, they can be direct probes of $λ_3^{}$. The proposed method is quite challenging; a relatively large statistics and polarized $e^+_{}e^-_{}$ beams are demanded. However, this is probably the only approach to directly measure $λ_3^{}$ in $e^+_{}e^-_{}$ collisions, when a beam energy above the $ZHH$ production threshold is not available.

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arXiv2018

Probing the scalar potential via double Higgs boson production at hadron colliders

We present a sensitivity study on the cubic and quartic self couplings in double Higgs production via gluon fusion at hadron colliders. Considering the relevant operators in the Standard Model Effective Field Theory up to dimension eight, we calculate the dominant contributions up to two-loop level, where the first dependence on the quartic interaction appears. Our approach allows to study the independent variations of the two self couplings and to clearly identify the terms necessary to satisfy gauge invariance and to obtain UV-finite results order by order in perturbation theory. We focus on the $b \bar b γγ$ signature for simplicity and provide the expected bounds for the cubic and quartic self couplings at the 14 TeV LHC with 3000 fb$^{-1}$ (HL-LHC) and for a future 100 TeV collider (FCC-100) with 30 ab$^{-1}$. We find that while the HL-LHC will provide very limited sensitivity on the quartic self coupling, precision measurements of double Higgs production at a FCC-100 will offer the opportunity to set competitive bounds. We show that combining information from double and triple Higgs production leads to significantly improved prospects for the determination of the quartic self coupling.

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arXiv2018

Trilinear Higgs coupling determination via single-Higgs differential measurements at the LHC

We study one-loop effects induced by an anomalous Higgs trilinear coupling on total and differential rates for the $H\to 4\ell$ decay and some of the main single-Higgs production channels at the LHC, namely, VBF, $VH$, $t\bar tH$ and $tHj$. Our results are based on a public code that calculates these effects by simply reweighting samples of Standard-Model-like events for a given production channel. For $VH$ and $t\bar tH$ production, where differential effects are particularly relevant, we include Standard Model electroweak corrections, which have similar sizes but different kinematic dependences. Finally, we study the sensitivity of future LHC runs to determine the trilinear coupling via inclusive and differential measurements, considering also the case where the Higgs couplings to vector bosons and the top quark is affected by new physics. We find that the constraints on the couplings and the relevance of differential distributions critically depend on the expected experimental and theoretical uncertainties.

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arXiv2018

Production of $HHH$ and $HHV(V=γ,Z)$ at the hadron colliders

We consider the production of two Higgs bosons in association with a gauge boson or another Higgs boson at the hadron colliders. We compute the cross sections and distributions for the processes $ p p \to H H H $ and $H H Z$ within the standard model. In particular, we compute the gluon-gluon fusion one-loop contributions mediated via heavy quarks in the loop. It is the leading order contribution to $ p p \to H H H $ process. To the process $ p p \to H H Z $, it is next-to-next-to-leading-order (NNLO) contribution in QCD coupling. We also compare this contribution to the next-to-leading-order (NLO) QCD contribution to this process. The NNLO contribution can be similar to NLO contribution at the Large Hadron Collider (LHC), and significantly more at higher center-of-mass energy machines. We also study new physics effects in these processes by considering $ttH, HHH, HHHH, HZZ$, and $HHZZ$ interactions as anomalous. The anomalous couplings can enhance the cross sections significantly. The $gg \to HHH$ process is specially sensitive to anomalous trilinear Higgs boson self-coupling. For the $gg \to HHZ$ process, there is some modest dependence on anomalous $HZZ$ couplings.

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arXiv2017

Mono-jet Signatures of Gluphilic Scalar Dark Matter

A gluphilic scalar dark matter (GSDM) model has recently been proposed as an interesting vision for WIMP dark matter communicating dominantly with the Standard Model via gluons. We discuss the collider signature of a hard jet recoiling against missing momentum ("mono-jet") in such a construction, whose leading contribution is at one-loop. We compare the full one-loop computation with an effective field theory (EFT) treatment, and find (as expected) that EFT does not accurately describe regions of parameter space where mass of the colored mediator particles are comparable to the experimental cuts on the missing energy. We determine bounds (for several choices of SU(3) representation of the mediator) from the $\sqrt{s}=$ 8 TeV data, and show the expected reach of the $\sqrt{s}=$ 13 TeV LHC and a future 100 TeV $pp$ collider to constrain or discover GSDM models.

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arXiv2016

Gluon fusion contribution to $HBB$ ($B = H,γ, Z$) at the LHC

We have calculated one-loop amplitudes for the production of Higgs boson in association with two electroweak bosons ($H,γ,Z$) via gluon-gluon fusion. We present preliminary results for the total cross section at 8, 13 and 100 TeV center-of-mass energies at $pp$ colliders. We study the interference effect and, also comment on the effect of new physics in terms of anomalous couplings of the Higgs boson in these processes.

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arXiv2016

Unraveling the CP phase of top-Higgs coupling in associated production at the LHC

We study the sensitivity of top polarization observables to the CP phase $ζ_t$ in the top Yukawa coupling in the process $pp\to thj$ at the 14 TeV high-luminosity run of the Large Hadron Collider (HL-LHC). We calculate the top polarization in this process as well as an azimuthal asymmetry of the charged lepton arising from the decay of the top in the lab frame. We find that the dependence of this lab-frame azimuthal asymmetry on the phase $ζ_t$ closely resembles the dependence of the top polarization on $ζ_t$. As compared to the cross section, which is sensitive to $ζ_t$ for larger values, the lepton azimuthal asymmetry can provide a sensitive measurement of $ζ_t$ for smaller values.

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arXiv2016

Distinguishing CP-odd couplings of the Higgs boson to weak boson pairs

We consider the observable effects of CP-violating anomalous $ZZh$ interaction arising from gauge invariant dimension-6 operators at the Large Hadron Collider (LHC), with the purpose of distinguishing them from not only the standard model effects but also those of CP-even anomalous interactions of similar nature. The postulation of a gauge invariant origin makes various couplings of this kind interrelated. The updated constraints from the LHC as well as limits from neutron and electron dipole moments are used in selecting the benchmark interaction strengths. We use some asymmetry parameters that have no contribution from standard or CP-even anomalous interactions. Parton showering and detector level simulation is included to make our analysis as realistic as possible. On the whole, we conclude that gauge invariant interaction of strength $\geq 40/\rm TeV^{2} $ can be successfully isolated using integrated luminosities in the 1.5-3.0 $\rm ab^{-1}$ range.

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arXiv2015

Unravelling the non-standard top and Higgs couplings in associated top-Higgs production at the High-luminosity LHC

We study the sensitivities of non-standard top and Higgs couplings in the $pp\to thj$ process at the 14 TeV high-luminosity run of Large Hadron Collider (HL-LHC). We calculate top polarization and construct various lab-frame observables to study their sensitivities on anomalous couplings at HL-LHC. Both anomalous Wtb and hVV couplings contribute in the production process. However, only the former contributes in top decay and only the latter takes part in Higgs decay. We study this interesting interplay of couplings in the production and decay observables. In production, these couplings significantly affect the top polarization. As a measure of top polarization, we look at decay-lepton angular distributions in the laboratory frame and study the effect of anomalous couplings on these distributions. We construct certain asymmetries to study the sensitivity of these distributions to top quark couplings. In particular, real and imaginary parts of an hVV coupling and real part of a Wtb coupling f2R significantly alter the top polarization and, in turn, affect the decay-lepton distributions in laboratory frame.

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