arXiv subjects

V. Ravindran

Publications and source records attributed to V. Ravindran.

At least 73 records · Page 4Linked to original sources

arXiv2015

Pseudo-scalar Higgs Boson Production at Threshold N$^3$LO and N$^3$LL QCD

We present the first results on the production of pseudo-scalar through gluon fusion at the LHC to N$^3$LO in QCD taking into account only soft gluon effects. We have used the effective Lagrangian that describes the coupling of pseudo-scalar with the gluons in the large top quark mass limit. We have used recently available quantities namely the three loop pseudo-scalar form factor and the third order universal soft function in QCD to achieve this. Along with the fixed order results, we also present the process dependent resummation coefficient for threshold resummation to N$^3$LL in QCD. Phenomenological impact of these threshold N$^3$LO corrections to pseudo-scalar production at the LHC is presented and their role to reduce the renormalisation scale dependence is demonstrated.

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arXiv2015

Spin-2 Form Factors at Three Loop in QCD

Spin-2 fields are often candidates in physics beyond the Standard Model namely the models with extra-dimensions where spin-2 Kaluza-Klein gravitons couple to the fields of the SM. Also, in the context of Higgs searches, spin-2 fields have been studied as an alternative to the scalar Higgs boson. In this article, we present the complete three loop QCD radiative corrections to the spin-2 quark-antiquark and spin-2 gluon-gluon form factors in SU(N) gauge theory with $n_f$ light flavors. These form factors contribute to both quark-antiquark and gluon-gluon initiated processes involving spin-2 particle in the hadronic reactions at the LHC. We have studied the structure of infrared singularities in these form factors up to three loop level using Sudakov integro-differential equation and found that the anomalous dimensions originating from soft and collinear regions of the loop integrals coincide with those of the electroweak vector boson and Higgs form factors confirming the universality of the infrared singularities in QCD amplitudes.

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arXiv2015

RG improved Higgs boson production to N$^3$LO in QCD

The recent result on the third order correction to the Higgs boson production through gluon fusion by Anastasiou et al. [1] not only provides a precise prediction with reduced scale uncertainties for studying the Higgs boson properties but also establishes the reliability of the perturbative QCD. In this letter, we propose a novel approach to further reduce the uncertainty arising from the renormalization scale by systematically resumming the renormalization group (RG) accessible logarithms to all orders in the strong coupling constant. Our numerical study based on this approach, demonstrates a significant improvement over the fixed order predictions.

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arXiv2014

Drell-Yan Production at Threshold to Third Order in QCD

The recent computation on the full threshold contributions to Higgs boson production at next-to-next-to-next-to-leading order (N$^3$LO) in QCD contains valuable information on the soft gluons resulting from virtual and real emission partonic subprocesses. We use those from the real emissions to obtain the corresponding soft gluon contributions to Drell-Yan production and determine the missing $δ(1-z)$ part of the N$^3$LO. The numerical impact of threshold effects demonstrates the importance of our results in the precision study with the Drell-Yan process at the LHC.

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arXiv2014

Rapidity Distributions in Drell-Yan and Higgs Productions at Threshold to Third Order in QCD

We present the threshold N$^3$LO perturbative QCD corrections to the rapidity distributions of dileptons in the Drell-Yan process and Higgs boson in gluon fusion. Sudakov resummation of QCD amplitudes, renormalization group invariance, and the mass factorization theorem provide useful guidelines to obtain them in an elegant manner. We use various state of the art three loop results that have been recently available to obtain these distributions. For the Higgs boson, we demonstrate numerically the importance of these corrections at the LHC.

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arXiv2014

Three photon production to NLO+PS accuracy at the LHC

In this paper, we present the next-to-leading order predictions for three photon production in the Standard Model, matched to the parton shower using the MC@NLO formalism. We have studied the role of parton shower on various observables and shown a selection of results for the 14 TeV LHC.

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arXiv2014

Associated production of Higgs boson with vector boson at threshold N$^3$LO in QCD

We present the results for the associated production of Higgs boson with vector boson computed at threshold N$^3$LO in QCD. We use the recently available result on the threshold contributions to the inclusive Drell-Yan production cross-section at third order in strong coupling constant. We have implemented it in the publicly available computer package vh@nnlo, thereby obtaining the numerical impact of threshold N$^3$LO contributions for the first time. We find that the inclusion of such corrections do reduce theoretical uncertainties resulting from the renormalization scale.

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arXiv2014

Higgs Rapidity Distribution in $b {\bar b}$ Annihilation at Threshold in N$^{3}$LO QCD

We present the rapidity distribution of the Higgs boson produced through bottom quark annihilation at third order in QCD using the threshold approximation. We provide a framework, based on the factorization properties of the QCD amplitudes along with Sudakov resummation and the renormalization group invariance, that allows one to perform the computation of the threshold corrections in a consistent, systematic and accurate way. The recent results on threshold N$^3$LO correction in QCD for the Drell-Yan production and on three loop QCD correction to Higgs form factor with bottom anti-bottom quark are used to achieve this task. We also demonstrate the numerical impact of these corrections at the LHC.

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arXiv2014

Two-Loop QCD Corrections to Higgs $\rightarrow b + \bar{b} + g$ Amplitude

Exclusive observables involving Higgs boson in association with jets are often well suited to study the Higgs boson properties. They are rates involving cuts on the final state jets or differential distributions of rapidity, transverse momentum of the observed Higgs boson. While they get dominant contributions from gluon initiated partonic subprocesses, it is important to include the subdominant ones coming from other channels. In this article, we study one such channel namely the Higgs production in association with a jet in bottom anti-bottom annihilation process. We compute relevant amplitude $H\rightarrow b+\overline b+g$ up to two loop level in QCD where Higgs couples to bottom quark through Yukawa coupling. We use projection operators to obtain the coefficients for each tensorial structure appearing in this process. We have demonstrated that the renormalized amplitudes do have the right infrared structure predicted by the QCD factorization in dimensional regularization. The finite parts of the one and two loop amplitudes are presented after subtracting the infrared poles using Catani's subtraction operators.

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arXiv2014

RS resonance in di-final state production at the LHC to NLO+PS accuracy

We study the di-final state processes ($\ell^+ \ell^-$, $γγ$, $ZZ$, $W^+ W^-$) to NLO+PS accuracy, as a result of both the SM and RS Kaluza-Klein graviton excitations. Decay of the electroweak gauge boson final states to different leptonic states are included at the showering stage. A selection of the results has been presented with PDF and scale uncertainties for various distributions. Using the di-lepton and di-photon final states, we present the search sensitivity, for the $14$ TeV LHC at $50$ fb$^{-1}$ luminosity.

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arXiv2014

Higgs boson production through $b \bar b$ annihilation at threshold in N$^3$LO QCD

We present threshold enhanced N$^3$LO QCD corrections to inclusive Higgs production through bottom anti-bottom annihilation at hadron colliders using threshold resummed cross section. The resummed cross section is obtained using factorization properties and Sudakov resummation of the inclusive cross section. We use the recent results on threshold N$^3$LO corrections in QCD for Drell-Yan production and three loop QCD corrections to Higgs form factor with bottom anti-bottom quark to achieve this task. This is the first step towards the evaluation of complete N$^3$LO result. We have numerically demonstrated the importance of such corrections at the LHC.

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arXiv2014

Two-Loop QCD Correction to massive spin-2 resonance $\rightarrow$ 3 gluons

We present the ${\cal O}(α_s^3)$ virtual QCD corrections to the process $h \rightarrow g+g+g$ due to interference of born and two-loop amplitudes, where $h$ is a massive spin-2 particle and $g$ is the gluon. We assume that the SM fields couple to $h$ through the SM energy momentum tensor. Our result constitutes one of the ingredients to full NNLO QCD contribution to production of a massive spin-2 particle along with a jet in the scattering process at the LHC. In particular, this massive spin-2 could be a KK mode of a ADD graviton in large extra dimensional model or a RS KK mode in warped extra dimensional model or a generic massive spin-2. In addition, it provides an opportunity to study the ultraviolet and infrared structures of QCD amplitudes involving tensorial coupling resulting from energy momentum operator. Using dimensional regularization, we find that infrared poles of this amplitude are in agreement with the proposal by Catani confirming the factorization property of QCD amplitudes with tensorial insertion.

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arXiv2014

Quark and gluon spin-2 form factors to two-loops in QCD

We present complete two-loop radiative corrections to the graviton-quark-antiquark form factor G^* \rightarrow q \overline q and graviton-gluon-gluon form factor G^* \rightarrow g g in SU(N) gauge theory with n_f light flavours using d-dimensional regularisation to all orders in \varepsilon=d-4. This is an important ingredient to next-to-next-to-leading order QCD corrections to hadronic scattering processes in models with large extra-dimensions where Kaluza-Klein graviton modes couple to Standard Model fields. We show that these form factors obey Sudakov integro-differential equation and the resulting cusp, collinear and soft anomalous dimensions coincide with those of electroweak vector boson and gluon form factors. We also find the universal behaviour of the infrared singularities in accordance with the proposal by Catani.

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arXiv2014

Drell-Yan, ZZ, W+W- production in SM & ADD model to NLO+PS accuracy at the LHC

In this paper, we present the next-to-leading order QCD corrections for di-lepton, di-electroweak boson (ZZ, W+W-) production in both the SM and the ADD model, matched to the HERWIG parton-shower using the aMC@NLO framework. A selection of results at the 8 TeV LHC, which exhibits deviation from the SM as a result of the large extra-dimension scenario are presented.

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arXiv2014

A framework for Higgs characterisation

We introduce a framework, based on an effective field theory approach, that allows one to perform characterisation studies of the boson recently discovered at the LHC, for all the relevant channels and in a consistent, systematic and accurate way. The production and decay of such a boson with various spin and parity assignments can be simulated by means of multi-parton, tree-level matrix elements and of next-to-leading order QCD calculations, both matched with parton showers. Several sample applications are presented which show, in particular, that beyond-leading-order effects in QCD have non-trivial phenomenological implications.

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arXiv2013

Next-to-Next-to-Leading Order QCD Corrections in Models of TeV-Scale Gravity

We compute the next-to-next-to-leading order QCD corrections to the graviton production in models of TeV-scale gravity, within the soft-virtual approximation. For the Arkani-Hamed, Dimopoulos and Dvali (ADD) model we evaluate the contribution to the Drell-Yan cross section, and we present distributions for the di-lepton invariant mass at the LHC with a center-of-mass energy $\sqrt{s_H}=14\text{TeV}$. We find a large $K$ factor ($K\simeq 1.8$) for large values of invariant mass, which is the region where the ADD graviton contribution dominates the cross section. The increase in the cross section with respect to the previous order result is larger than $10\%$ in the same invariant mass region. We also observe a substantial reduction in the scale uncertainty. For the Randall-Sundrum (RS) model we computed the total single graviton production cross section at the LHC. We find an increase between $10\%$ and $13\%$ with respect to the next-to-leading order prediction, depending on the model parameters. We provide an analytic expression for the NNLO $K$ factor as a function of the lightest RS graviton mass.

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arXiv2012

Diphoton production in the ADD model to NLO+parton shower accuracy at the LHC

In this paper, we present the next-to-leading order predictions for diphoton production in the ADD model, matched to the HERWIG parton shower using the MC@NLO formalism. A selection of the results is presented for d=2-6 extra dimensions, using generic cuts as well as analysis cuts mimicking the search strategies as pursued by the ATLAS and CMS experiments.

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arXiv2012

Neutral triple electroweak gauge boson production in the large extra-dimension model at the LHC

We study the prospects of probing large extra dimension model at the LHC through neutral triple gauge boson production processes. In theories with extra dimensions these processes result from the exchange of a tower of massive graviton modes between the SM particles. We consider γγγ, γγZ, γZ Z and ZZZ production processes, and present our results for various kinematic distributions at the LHC for \sqrt{S}=14 TeV.

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