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Pulak Banerjee

Publications and source records attributed to Pulak Banerjee.

At least 19 recordsLinked to original sources

Two-loop QCD corrections to $ H \rightarrow b + \bar{b} + g $ at higher powers in the dimensional regulator

We compute the two-loop massless QCD corrections to the amplitude of Higgs boson decay to bottom quark pair and a gluon ($H \rightarrow b + \bar{b} + g$) in the higher powers of the dimensional regularization parameter $\epsilon$. The calculation is performed by projecting the amplitude onto the appropriate Lorentz structures related to the process. We also show the numerical behaviour of the form factors for a few sample phase-space points. These amplitudes are necessary ingredients for computing the three-loop virtual corrections to bottom-quark annihilation to Higgs plus jet production at the hadron collisions.

hep-ph

Associated $ZH$ production in gluon fusion process at NLO+NLL

We present precise results for invariant mass distributions and inclusive cross-sections, of associated $ZH$ production through gluon fusion in QCD. We include threshold logarithms at next-to-leading-logarithmic (NLL) accuracy and match the results to full next-to-leading-order (NLO) results with exact top-quark mass dependence in the virtual amplitudes. At 13.6 TeV energy at LHC, the NLO+NLL cross-section increases the NLO counterpart by about $20\%$. For differential distributions, at 3000 GeV, the uncertainties arising out of the unphysical renormalization and factorization scales is about $20\%$ for NLO; whereas for the resummed results it is around $12\%$. We also combine these results to the Drell-Yan type results at N$^3$LL and present the most precise results in hadron collisions.

hep-ph

QCD corrections for Pseudoscalar Higgs decay to 3 partons at higher orders in dimensional regulator

In this contribution, we present our recent study on the second-order corrections of pseudo-scalar($A$) Higgs decay to three partons, at higher orders in the dimensional regulator. We have studied the one and two-loop amplitudes for processes, $A\to ggg$ and $A\to q\bar{q}g$ in the effective theory framework. Our results, after suitable crossings of the external momenta, are important ingredients for predicting the differential distribution of the pseudo-scalar Higgs boson in association with a jet at hadron colliders.

hep-ph

VV Resummation To NNLO+NNLL At the LHC

We present the resummed predictions for a vector boson pair production at the LHC. We have performed threshold resummation to next-to-next-to-leading logarithmic (NNLL) accuracy, and then matched them to next-to-next-to-leading order (NNLO) QCD results. After resummation, we observe a reduction in the scale uncertainties arising from unphysical renormalization and factorization scales. We find that the resummed corrections add a few per cent to the fixed order results for both ZZ and WW production.

hep-ph

Threshold resummation for $W$-boson pair production at NNLO+NNLL

We present results for threshold resummation of the invariant mass distribution, for on-shell production of a pair of $W$-bosons at next-to-next-to-leading order + next-to-next-to-leading logarithmic (NNLO+NNLL) accuracy in QCD. Owing to its sensitivity to the self-interactions between gauge bosons, this process is important to investigate at the energies of the Large Hadron Collider (LHC). We achieve this resummation by exploiting the factorization properties of the soft and virtual parts of the partonic cross-section. Our analysis has been carried out for the invariant mass distribution up to $Q$ = 2500 GeV. At this highest $Q$ we find that, for 13.6 TeV LHC, the NNLL resummation enhances the NNLO cross-sections by about $6.3\%$ and reduces the conventional scale uncertainties from 6.8\% at NNLO to 4.1\% at NNLO+NNLL. We also estimate the intrinsic uncertainties due to the non-perturbative parton distribution functions at the highest perturbative order, for both fixed-order and resummed results, to be around 3\% for $Q \sim$ 2000 GeV.

hep-ph

Threshold resummation for $ZZ$ production

We briefly review the status of threshold resummation for two massive $Z$-bosons in the Standard Model. We discuss some recent results for $Z$-boson pair production at next-to-next-to-leading order + next-to-next-to-leading logarithmic accuracy.

hep-ph

Pseudoscalar Higgs boson decay to three parton amplitudes at NNLO to higher orders in the dimensional regulator

We present for the first time the second-order corrections of pseudo-scalar($A$) Higgs decay to three parton to higher orders in the dimensional regulator. We compute the one and two-loop amplitudes for processes, $A\to ggg$ and $A\to q\bar{q}g$ in the effective theory framework. With suitable crossing of the external momenta, these calculations are well-suited for predicting the differential distribution of pseudo-scalar Higgs in association with a jet at hadron colliders, up to next-to-next-to-leading order (NNLO) in the strong coupling constant. These results expanded to higher orders in dimensional regulator will contribute to the full three loop cross section. We implement the finite pieces of the amplitudes in a numerical code which can be used with any Monte Carlo phase space generator.

hep-ph

Threshold resummation for $Z$-boson pair production at NNLO+NNLL

The production of a pair of on-shell $Z$-bosons is an important process at the Large Hadron Collider. Owing to its large production cross section at the LHC, this process is very useful for SM precision studies, electroweak symmetry breaking sector as well as to unravel the possible new physics. In this work, we have performed the threshold resummation of the large logarithms that arise in the partonic threshold limit $z \to 1$, up to Next-to-Next-to-Leading Logarithmic (NNLL) accuracy. The presence of the two-loop contributions in the process dependent resummation coefficient $g_0$ makes the numerical computation a non-trivial task. After matching the resummed predictions to the Next-to-Next-to-Leading order (NNLO) fixed order results, we present the invariant mass distribution to NNLO+NNLL accuracy in QCD for the current LHC energies. We find that in the high invariant mass region ($Q=1$ TeV), while the NNLO corrections are as large as $83\%$ with respect to the leading order, the NNLL contribution enhances the cross section by additional few percent, about $4\%$ for $13.6$ TeV LHC. In this invariant mass region, the conventional scale uncertainties in the fixed order results get reduced from $3.4\%$ at NNLO to about $2.6\%$ at NNLO+NNLL, and this reduction is expected to be more for higher $Q$ values.

hep-ph

Bhabha scattering at NNLO with next-to-soft stabilisation

A critical subject in fully differential QED calculations originates from numerical instabilities due to small fermion masses that act as regulators of collinear singularities. At next-to-next-to-leading order (NNLO) a major challenge is therefore to find a stable implementation of numerically delicate real-virtual matrix elements. In the case of Bhabha scattering this has so far prevented the development of a fixed-order Monte Carlo at NNLO accuracy. In this paper we present a new method for stabilising the real-virtual matrix element. It is based on the expansion for soft photon energies including the non-universal subleading term calculated with the method of regions. We have applied this method to Bhabha scattering to obtain a stable and efficient implementation within the McMule framework. We therefore present for the first time fully differential results for the photonic NNLO corrections to Bhabha scattering.

hep-ph

M{\o}ller scattering at NNLO

We present a calculation of the full set of next-to-next-to-leading-order QED corrections to unpolarised M{\o}ller scattering. This encompasses photonic, leptonic, and non-perturbative hadronic corrections and includes electron mass effects as well as hard photon radiation. The corresponding matrix elements are implemented in the Monte Carlo framework McMule allowing for the computation of fully-differential observables. As a first application we show results tailored to the kinematics and detector design of the PRad II experiment where a high-precision theory prediction for M{\o}ller scattering is required to achieve the targeted precision. We observe that the corrections become essential to reliably calculate the corresponding differential distributions especially in regions where the leading-order contribution is absent.

hep-ph

Form factors with two operator insertions and the principle of maximal transcendentality

We present the first calculations of two-point two-loop form factors (FFs) with a two identical operators insertion in maximally supersymmetric Yang-Mills theory. In this article, we consider the supersymmetry protected half-BPS primary and unprotected Konishi operators. Unlike the FFs of a single operator insertion of the half-BPS primary, the FFs involving two half-BPS operators are found to contain lower transcendentality weight terms in addition to the highest ones. Moreover, in contrast to Sudakov FFs, the highest weight terms of the FFs of a double half-BPS no longer match with that of a double Konishi. We also find that the principle of maximal transcendentality, which dictates the presence of identical highest weight terms in the scalar FFs of half-BPS and quark/gluon FFs in QCD, does not hold true anymore for insertions of two identical operators. We discover the absence of any additional ultraviolet counterterm that could arise from the contact interaction between two composite operators.

hep-th

Infrared structure of $\mathcal{N}$ = 4 SYM and leading transcendentality principle in gauge theory

We present a detailed study on the infrared structure of $\mathcal{N}=4$ SYM and its connection to QCD. Calculation of collinear splitting functions helps to understand the structure and thus one can get infrared safe cross sections. We also demonstrate the factorization property that soft plus virtual part of the cross section satisfies and through factorization, we calculate soft distribution function up to third order in perturbation theory. We show that the soft distribution function is process independent that includes operators as well as external legs. In addition to this we compare our findings against the known results in QCD through principle of maximum transcendentality (PMT). We extend our analysis further for the case of three-point form factors involving stress tensor and find that it violates the PMT while comparing with the corresponding quantity in the standard model, observed for the first time at the level of form factor.

hep-th

The Curious Case of Leading Transcendentality: Three Point Form Factors

Form factors are important ingredients to investigate the principle of maximal transcendentality (PMT) and to extract anomalous dimensions of local gauge invariant operators. In this article, we compute several two- and three-point FFs to three- and two-loops, respectively, for three different choices of local gauge invariant operators in ${\cal N}=4$ super Yang-Mills (SYM) theory. The operators ${\cal O}^1$ and ${\cal O}^2$ are flavour and helicity blind configurations of supersymmetric descendant of the half-BPS and Konishi primary, respectively, and ${\cal O}^3$ is the energy-momentum tensor. The operators ${\cal O}^1$ and ${\cal O}^2$ are composed of non-protected dimension-three (classical) fermionic and scalar components belonging to SU($2|3$) closed sub-sector of ${\cal N}=4$ SYM. We analyse the mixing among the non-protected fermionic and scalar components of these operators up to three-loops in perturbation theory and consequently, compute the quantum corrections to the corresponding dilatation operators. The highest transcendental (HT) weight terms of the FFs of ${\cal O}^1$ are found to be independent of the external on-shell states and, moreover, those are equal to that of half-BPS, however, this does not hold true for the FFs of ${\cal O}^2$. FFs of the ${\cal O}^3$ exhibit identical behaviours to that of half-BPS, in concordance with the classical expectations. However, the three-point FFs of ${\cal O}^3$ violate the PMT while comparing with the corresponding quantity in the standard model, observed for the first time at the level of FF.

hep-th

NNLO QCD$\oplus$QED corrections to Higgs production in bottom quark annihilation

We present next-to-next-to leading order (NNLO) quantum electrodynamics (QED) corrections to the production of the Higgs boson in bottom quark annihilation at the Large Hadron Collider (LHC) in the five flavor scheme. We have systematically included the NNLO corrections resulting from the interference of quantum chromodynamics (QCD) and QED interactions. We have investigated the infrared (IR) structure of the bottom quark form factor up to two loop level in QED and in QCD$\times$QED using K+G equation. We find that the IR poles in the form factor are controlled by the universal cusp, collinear and soft anomalous dimensions. In addition, we derive the QED as well as QCD$\times$QED contributions to soft distribution function as well as to the ultraviolet renormalization constant of the bottom Yukawa coupling up to second order in strong coupling and fine structure constant. Finally, we report our findings on the numerical impact of the NNLO results from QED and QCD$\times$QED at the LHC energies taking into account the dominant NNLO QCD corrections.

hep-ph

Higgs pair production from bottom quark annihilation to NNLO in QCD

We present the first results on the two-loop massless QCD corrections to the four-point amplitude $b+\overline{b} \rightarrow H+H$ in the five flavor scheme, treating bottom quarks as massless. This amplitude is sensitive to the trilinear Higgs boson coupling. Our two-loop result for this amplitude constitutes of purely virtual contributions to the next-to-next-to-leading order QCD predictions for the production of a pair of Higgs bosons at the Large Hadron Collider. Using these two loop amplitudes and exploiting the universality of the soft contributions in perturbative QCD, we obtain the NNLO QCD effects in the soft plus virtual approximation. We find that the inclusion of higher order terms reduce the uncertainties resulting from the unphysical renormalisation and factorisation scales.

hep-ph

Second order splitting functions and infrared safe cross sections in $\mathcal{N}=4$ SYM theory

We report our findings on the perturbative structure of ${\cal N}=4$ supersymmetric Yang-Mills (SYM) theory in the infrared sector by computing inclusive scattering cross sections of on-shell particles. We use half-BPS, energy-momentum tensor and Konishi operators to produce singlet states in the scattering processes to probe the soft and the collinear properties of the cross sections. By appropriately defining the infrared safe observables, we obtain collinear splitting functions up to second order in the perturbation theory. The splitting functions and the infrared finite cross sections demonstrate several interesting connections with those in the perturbative QCD. We also determine the process independent soft distribution function up to third order in the perturbation theory and show that it is universal {\it i.e.} independent of the operators as well as the external states. Interestingly, the soft distribution function in ${\cal N}=4$ SYM theory matches exactly with the leading transcendental part of the corresponding one in the QCD. This enables us to predict the third order soft plus virtual cross section for the production of the on-shell singlet states.

hep-th

Resummed transverse momentum distribution of pseudo-scalar Higgs boson at NNLO$_A$+NNLL

In this article we have studied the transverse momentum distribution of the pseudo-scalar Higgs boson at the Large Hadron Collider (LHC). The small $\pt$ region which provides the bulk of the cross section is not accessible to fixed order perturbation theory due to the presence of large logarithms in the series. Using the universal infrared behaviour of the QCD we resum these large logarithms up to next-to-next-to-leading logarithmic (NNLL) accuracy. We observe a significant reduction in theoretical uncertainties due to the unphysical scales at NNLL level compared to the previous order. We present the $p_T$ distribution matched to NNLO$_A$+NNLL, valid for the whole $p_T$ region and provide a detailed phenomenological study in the context of both 14 TeV and 13 TeV LHC using different choices of masses, scales and parton distribution functions which will be useful for the search of such particle at the LHC in near future.

hep-ph

Two-loop massless QCD corrections to the $g+g \rightarrow H+H$ four-point amplitude

We compute the two-loop massless QCD corrections to the four-point amplitude $g+g \rightarrow H+H$ resulting from effective operator insertions that describe the interaction of a Higgs boson with gluons in the infinite top quark mass limit. This amplitude is an essential ingredient to the third-order QCD corrections to Higgs boson pair production. We have implemented our results in a numerical code that can be used for further phenomenological studies.

hep-ph