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Riccardo Torre

Publications and source records attributed to Riccardo Torre.

49 records · Page 3Linked to original sources
arXiv2012

Higgs decay with monophoton + MET signature from low scale supersymmetry breaking

We study the decay of a standard model-like Higgs boson into a gravitino and a neutralino, which subsequently decays promptly into another gravitino and a photon. Such a decay can be important in scenarios where the supersymmetry breaking scale is of the order of a few TeV, and in the region of low transverse momenta of the photon, it may provide the dominant contribution to the final state with a photon and two gravitinos. We estimate the relevant standard model backgrounds and the prospects for discovering this Higgs decay through a photon and missing transverse energy signal at the LHC in terms of a simplified model. We also give an explicit model with manifest, but spontaneously broken, supersymmetry in which the usual MSSM soft terms are promoted to supersymmetric operators involving a dynamical goldstino supermultiplet. This model can give rise to a SM-like CP-even neutral Higgs particle with a mass of 125 GeV, without requiring substantial radiative corrections, and with couplings sufficiently large for a signal discovery through the above mentioned Higgs decay channel with the upcoming data from the LHC.

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arXiv2012

Photophilic Higgs from sgoldstino mixing

The spontaneous breaking of linearly realized N=1 supersymmetry implies the existence of a pseudo-Goldstone fermion, the goldstino, and of its complex scalar superpartner, the sgoldstino. The latter has generically sizable tree-level couplings to Standard Model gauge bosons while its couplings to SM fermions are suppressed. We consider a light sgoldstino, with a mass around 1 TeV, that mixes with a SM-like Higgs scalar at around 125 GeV. We show that such a mixing can enhance the Higgs to di-photon signal rate while evading all the relevant experimental bounds and without significantly affecting the other decay channels.

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arXiv2012

An isosinglet W' at the LHC: updated bounds from direct searches

We study the implications of the latest LHC searches for resonances in the di-jet and di-boson final states and for quark compositeness in the di-jet angular distributions on an iso-singlet W' with unit hypercharge. Predictions presented in previous papers are collected and updated to take into account all the present bounds from direct searches. It turns out that bounds on the coupling to quarks coming from the LHC measurements of di-jet angular distributions are starting to be competitive with the ones coming from direct searches in the di-jet invariant mass spectrum. Moreover, the stringent bounds on the mixing angle coming from the new searches in the $WZ\to l^{+}l^{-}lν$ final state, imply, in the case of discovery, the necessity to go to the LHC with $\sqrt{s}=14$ TeV to be able to probe interesting masses and couplings relevant for the W' decay into the Wγ final state, particularly relevant to get more insight on the nature of the new vector.

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arXiv2011

A "composite" scalar-vector system at the LHC

In the framework of a strong dynamics for Electro-Weak Symmetry Breaking (EWSB), both vector and scalar degrees of freedom have been studied in the literature within an effective Lagrangian approach. Here we consider the case in which both a scalar, $h$, and a vector, $V$ - respectively an iso-singlet and an iso-triplet under a custodial SU(2) - are relevant with a mass below the cut-off $Λ\approx 4πv$. We study the amplitudes for the processes $W_L W_L \to W_L W_L, hh, V_{L}V_{L}, V_{L}h$. Requiring unitarity for the elastic channel $W_L W_L \to W_L W_L$ we can reduce the parameter space to two free parameters for given masses of the heavy vector and the scalar. We study the numerical total cross sections for the associated productions $pp\to Vhjj$ by Vector Boson Fusion (VBF) and $pp\to Vh$ by Drell-Yan (DY) annihilation as functions of these free parameters. The expected rates of same-sign di-lepton and tri-lepton events from the decay of the $Vh$ final state are also given.

hep-ph↗
arXiv2011

Narrow resonances at the early LHC

We discuss the possibility to observe new resonances at the early LHC using a phenomenological approach. We show predictions for the production of a scalar in the gg-channel and an heavy quark in the qg-channel and we compare them with the recent results of the ATLAS and CMS experiments in the di-jet channel, setting upper limits on the relevant couplings. We finally discuss the importance of the final states containing at least one photon making sensitivity predictions for the corresponding couplings.

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arXiv2011

Strong, weak and flavor scalar triplets for the CDF Wjj anomaly

A model describing the 4.1σ Wjj anomaly observed by the CDF experiment at the Tevatron collider is introduced. It features new scalar particles which are charged both under the SU(3)_C and the SU(2)_L gauge groups and which couple to pairs of quarks. We introduce several identical replicas of the scalar multiplets in order to leave an unbroken U(3)_Q x U(3)_U x U(3)_D flavor symmetry to satisfy the constraints coming from flavor physics. We discuss the LHC reach on the new scalar resonances both in the resonant production channel (with the Wjj final state) and in the QCD pair production channel (with the 4j final state).

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arXiv2011

Signals of composite particles at the LHC

Composite particles generated by an unknown strong dynamics can be responsible for the ElectroWeak Symmetry Breaking (EWSB) and can substitute the Standard Model (SM) Higgs boson in keeping perturbative unitarity in the longitudinal WW scattering up to a cut-off Λ\approx 4πv. These new states can be sufficiently light to be observed at the Large Hadron Collider (LHC) and they can even be the first manifestation of new physics at the LHC. Their couplings among themselves and with the SM particles, can be described using reasonable effective Lagrangians and Chiral Perturbation Theory. In the first part of this thesis different possibilities for a strongly interacting EWSB are discussed in details with particular attention to the roles of unitarity in the longitudinal WW scattering and of ElectroWeak Precision Tests (EWPT). Higgsless models with composite vectors and scalars, based on the SU(2)_{L}\times SU(2)_{R}/SU(2)_{L+R} custodial symmetry, are discussed in the context of ElectroWeak Chiral Lagrangians and the phenomenology of the pair productions is studied for the high energy and high luminosity phase of the LHC. In the second part of the thesis the possible signals of single particle production at the early LHC, with 7 TeV of center of mass energy and 1-5 fb^{-1} of integrated luminosity, are treated with a phenomenological Lagrangian approach. The final states containing at least one photon emerge as the most promising channels for an early discovery already with tens of inverse picobarns of integrated luminosity. Finally, in the last part of this work, the role of a composite iso-singlet vector in Dark Matter models is discussed and the related LHC phenomenology is studied, giving particular attention to the Zγfinal state.

hep-ph↗
arXiv2011

A weakly constrained W' at the early LHC

We study, within an effective approach, the phenomenology of a charged W' vector which transforms as an isosinglet under the Standard Model gauge group. We discuss bounds from present data, finding that these are quite weak for suitable choices of the right-handed quark mixing matrix. Then we study the resonant production at the early LHC of such a weakly constrained W'. We start discussing the reach in the dijet final state, which is one of the channels where the first W' signal would most likely appear, and then we analyse prospects for the more challenging discovery of W' decays into Wγ and WZ. We show in particular that the former can be used to gain insight on the possibly composite nature of the resonance.

hep-ph↗
arXiv2010

Signals of single particle production at the earliest LHC

Based on simple phenomenological Lagrangians, fulfilling reasonable consistency conditions, we consider under which circumstances the production of a single particle might be an early signal of new physics at the LHC. Effective final states are $γγ$ and $γ+jet$ already with tens of inverse picobarns of integrated luminosity at 7 TeV.

hep-ph↗
arXiv2010

Associated scalar-vector production at the LHC within an effective Lagrangian approach

We consider the case in which a strong dynamics is responsible for Electro-Weak Symmetry Breaking (EWSB) and both a scalar $h$ and a vector $V$, respectively a singlet and a triplet under a custodial $SU\left(2\right)$, are relevant and have a mass below the cut-off $Λ\approx 4πv$. In this framework we study the total cross sections for the associated $Vh$ production at the LHC at 14 TeV as functions of two independent free parameters.

hep-ph↗
arXiv2010

Composite Vectors at the Large Hadron Collider

An unspecified strong dynamics may give rise to composite vectors sufficiently light that their interactions, among themselves or with the electroweak gauge bosons, be approximately described by an effective Lagrangian invariant under $SU(2)_L\times SU(2)_R/ SU(2)_{L+R}$. We study the production at the LHC of two such states by vector boson fusion or by the Drell--Yan process in this general framework and we compare it with the case of gauge vectors from a $SU(2)_L\times SU(2)_R\times SU(2)^N$ gauge model spontaneously broken to the diagonal SU(2) subgroup by a generic $σ$-model. Special attention is payed to the asymptotic behaviour of the different amplitudes in both cases. The expected rates of multi-lepton events from the decay of the composite vectors are also given. A thorough phenomenological analysis and the evaluation of the backgrounds to such signals, aiming at assessing the visibility of composite-vector pairs at the LHC, is instead deferred to future work.

hep-ph↗
arXiv2010

Signals of composite electroweak-neutral Dark Matter: LHC/Direct Detection interplay

In a strong-coupling picture of ElectroWeak Symmetry Breaking, a composite electroweak-neutral state in the TeV mass range, carrying a global (quasi-)conserved charge, makes a plausible Dark Matter (DM) candidate, with the ongoing direct DM searches being precisely sensitive to the expected signals. To exploit the crucial interplay between direct DM searches and the LHC, we consider a composite iso-singlet vector $V$, mixed with the hypercharge gauge field, as the essential mediator of the interaction between the DM particle and the nucleus. Based on a suitable effective chiral Lagrangian, we give the expected properties and production rates of $V$, showing its possible discovery at the maximal LHC energy with about 100 fb^{-1} of integrated luminosity.

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