Archivio della ricerca di Triestehttps://arts.units.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Fri, 03 Apr 2020 08:41:18 GMT2020-04-03T08:41:18Z10971Exponentially spread dynamical Yukawa couplings from non-perturbative chiral symmetry breaking in the dark sectorhttp://hdl.handle.net/11368/2757357Titolo: Exponentially spread dynamical Yukawa couplings from non-perturbative chiral symmetry breaking in the dark sector
Abstract: We propose a new paradigm for generating exponentially spread standard model Yukawa couplings from a new U(1)F gauge symmetry in the dark sector. Chiral symmetry is spontaneously broken among dark fermions that obtain nonvanishing masses from a nonperturbative solution to the mass gap equation. The necessary ingredient for this mechanism to work is the existence of higher-derivative terms in the dark U(1)F theory, or equivalently the existence of Lee–Wick ghosts, that (i) allow for a nonperturbative solution to the mass gap equation in the weak coupling regime of the Abelian theory and (ii) induce exponential dependence of the generated masses on dark fermion U(1)F quantum numbers. The generated flavor and chiral symmetry breaking in the dark sector is transferred to the standard model Yukawa couplings at the one-loop level via Higgs portal-type scalar messenger fields. The latter carry quantum numbers of squarks and sleptons. A new intriguing phenomenology is predicted that could be potentially tested at the LHC, provided the characteristic mass scale of the messenger sector is accessible at the LHC as is suggested by naturalness arguments.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11368/27573572014-01-01T00:00:00ZAsking for an extra photon in Higgs production at the LHC and beyondhttp://hdl.handle.net/11368/2886117Titolo: Asking for an extra photon in Higgs production at the LHC and beyond
Abstract: We study the inclusive production of a Higgs boson in association with a high-pT photon at the LHC, detailing the leading-order features of the main processes contributing to the Hγ final state. Requiring an extra hard photon in Higgs production upsets the cross-section hierarchy for the dominant channels. The Hγ inclusive production comes mainly from photons radiated in vector-boson fusion (VBF), which accounts for about 2/3 of the total rate, for pT^(γ,jT)>30 GeV, at leading order. On the other hand, radiating a high-pT photon in the main top-loop Higgs channel implies an extra parton in the final state, which suppresses the production rate by a further αS power. As a result, the Hγ production via top loops at the LHC has rates comparable with the ones arising from either the Htt¯ production or the HW(Z)γ associated production. Then, in order of decreasing cross section, comes the single-top-plus-Higgs channel, followed in turn by the heavy-flavor fusion processes bb¯→Hγ and c barc→Hγ. The Hγ production via electroweak loops has just a minor role. At larger c.m. energies, the Httbar-γ channel surpasses the total contribution of top-loop processes. In particular, requiring pT(γ,j)>30 GeV at Sqrt(S)≃100 TeV, Htt¯γ accounts for about 1/4 of the inclusive Hγ production at leading order, about half of the total being due to VBF production.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/11368/28861172016-01-01T00:00:00ZHiggs-boson production in association with a dark photon in e+e− collisionshttp://hdl.handle.net/11368/2885445Titolo: Higgs-boson production in association with a dark photon in e+e− collisions
Abstract: We study the production of a Higgs boson recoiling from a massless invisible system in e+e− collisions. This is a quite distinctive signature that can arise when the Higgs boson is produced in association with a massless dark photon, which can happen in BSM scenarios foreseeing an extra unbroken U(1) gauge group. Dark photons can indeed acquire effective couplings to the Higgs boson as occurs in models recently proposed to generate exponentially-spread Yukawa couplings. We analyze the signal and corresponding backgrounds for H→bb,, and estimate ILC and FCC-ee sensitivities in a model-independent way.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/11368/28854452015-01-01T00:00:00ZA SUSY inspired simplified model for the 750 GeV diphoton excesshttp://hdl.handle.net/11368/2886097Titolo: A SUSY inspired simplified model for the 750 GeV diphoton excess
Abstract: The evidence for a new neutral scalar particle from the 750 GeV diphoton excess, and the absence of any other signal of new physics at the LHC so far, suggests the existence of new coloured scalars. To study this possibility, we propose a supersymmetry inspired simplified model, extending the Standard Model with a singlet scalar and with heavy scalar fields carrying both colour and electric charges – new scalar quarks. To allow the latter to decay, and to generate the dark matter of the Universe, we also add a neutral fermion to the particle content. We show that this model provides a two-parameter fit to the observed diphoton excess consistently with cosmology, while the allowed parameter space is bounded by the consistency of the model. In the context of our simplified model this implies the existence of other supersymmetric particles accessible at the LHC, rendering this scenario falsifiable.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/11368/28860972016-01-01T00:00:00ZEnhancing the ttH signal through top-quark spin polarization effects at the LHChttp://hdl.handle.net/11368/2886127Titolo: Enhancing the ttH signal through top-quark spin polarization effects at the LHC
Abstract: We consider the impact of the ￼ spin correlations in the Higgs boson production in association with top quark pairs ￼ and in the corresponding backgrounds. We study the ￼ and H→γγ decay modes. We show that retaining the ￼ spin-correlation effects could significantly improve the LHC sensitivity to the ￼ signal, particularly in the H→γγ channel.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/11368/28861272016-01-01T00:00:00ZPolarization observables for millicharged particles in photon collisionshttp://hdl.handle.net/11368/2886364Titolo: Polarization observables for millicharged particles in photon collisions
Abstract: Particles in a hidden sector can potentially acquire a small electric charge through their interaction with the Standard Model and consequently be observed as millicharged particles. We systematically compute the production of millicharged scalar, fermion and vector boson particles in collisions of polarized photons. The presented calculation is model independent and is based purely on the assumptions of electromagnetic gauge invariance and unitarity. Polarization observables are evaluated and analyzed for each spin case. We show that the photon polarization asymmetries are a useful tool for discriminating between the spins of the produced millicharged particles. Phenomenological implications for searches of millicharged particles in dedicated photon-photon collision experiments are also discussed.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/11368/28863642016-01-01T00:00:00ZDark-photon searches via Higgs-boson production at the LHChttp://hdl.handle.net/11368/2886123Titolo: Dark-photon searches via Higgs-boson production at the LHC
Abstract: Dark photons γ¯ mediating long-range forces in a dark sector are predicted by various new physics scenarios, and are being intensively searched for in experiments. We extend a previous study of a new discovery process for dark photons proceedings via Higgs-boson production at the LHC. Thanks to the non-decoupling properties of the Higgs boson, BR(H→γγ¯) values up to a few percent are possible for a massless dark photon, even for heavy dark-sector scenarios. The corresponding signature consists (for a Higgs boson at rest) of a striking monochromatic photon with energy Eγ=mH/2, and similar amount of missing energy. We perform a model independent analysis at the LHC of both the gluon-fusion and VBF Higgs production mechanisms at 14 TeV, including parton-shower effects, and updating our previous parton-level analysis at 8 TeV in the gluon-fusion channel by a more realistic background modeling. We find that a 5σ sensitivity can be reached in the gluon-fusion channel for BR(H→γγ¯)≃0.1% with an integrated luminosity of L≃300fb−1. The corresponding VBF reach is instead restricted to 1%. Such decay rates can be naturally obtained in dark-photon scenarios arising from unbroken U(1)F models explaining the origin and hierarchy of the Yukawa couplings, strongly motivating the search for this exotic Higgs decay at the LHC.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/11368/28861232016-01-01T00:00:00ZDirect constraints on the top-Higgs coupling from the 8 TeV LHC datahttp://hdl.handle.net/11368/2885988Titolo: Direct constraints on the top-Higgs coupling from the 8 TeV LHC data
Abstract: The LHC experiments have analyzed the 7 and 8 TeV LHC data in the main Higgs production
and decay modes. Current analyses show a near degeneracy in the relative sign of the Htt¯and
HWW couplings. In order to remove this degeneracy and strongly constrain these couplings we
have consider single top production in association with a Higgs in the t-channel. This process
can be very sensitive to both the magnitude and the sign of a non-standard top-Higgs coupling.
We show that at 8 TeV center of mass energy and 50 fb−1 integrated luminosity the combination of diphoton and multi-lepton signatures, originating from different combinations of the top and
Higgs decay modes, can be a potential probe to constrain a large portion of the negative top-Higgs
coupling space presently allowed by the ATLAS and CMS global fits.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/11368/28859882013-01-01T00:00:00ZDark matter and spin-1 milli-charged particleshttp://hdl.handle.net/11368/2885990Titolo: Dark matter and spin-1 milli-charged particles
Abstract: New physics scenarios beyond the Standard Model predict the existence of milli-charged particles. So far, only spin-1/2 and spin-0 milli-charged particles have been considered in literature, leaving out the interesting case of spin-1. We propose a minimal unitary and renormalizable model of massive milli-charged vector particles. Unitarity requires that these particles are gauge bosons of a non-abelian spontaneously broken gauge symmetry. The minimal scenario then consists of an extended Standard Model gauge group SU(2)L × U(1)Y × SU(2)D together with a SU(2)D dark Higgs boson responsible for the symmetry breaking in the dark sector. By imposing that the dark Higgs multiplet has a non-vanishing milli-hypercharge, stable milli-charged spin-1 fields arise thereby providing a potential dark matter candidate. We analyse the phenomenological constraints on this scenario and discuss their implications.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/11368/28859902015-01-01T00:00:00ZImplications of effective axial-vector coupling of gluon for tt[over ¯] spin polarizations at the LHChttp://hdl.handle.net/11368/2691199Titolo: Implications of effective axial-vector coupling of gluon for tt[over ¯] spin polarizations at the LHC
Abstract: We analyze the impact of effective axial-vector coupling of the gluon on spin polarization observables in $t\bar{t}$ pair production at the LHC. Working at leading order in QCD, we compute the $t\bar{t}$ spin-correlation and left-right spin asymmetry coefficients in the helicity basis in the laboratory frame as functions of the new physics scale $\Lambda$ associated with this coupling. We found that the $t\bar{t}$ invariant mass dependent asymmetries are more sensitive to the scale $\Lambda$ than the corresponding inclusive ones, in particular when suitable cuts selecting high $t\bar{t}$ invariant mass regions are imposed. In the context of this scenario, we show that the LHC has potential either to confirm or to rule out the Tevatron FB top asymmetry anomaly by analyzing the $t\bar{t}$ spin-correlation and left-right polarization asymmetries. On the other hand, stringent lower bound on the new physics scale $\Lambda$ can be set in this scenario if no significant deviations from the SM predictions for those observables will be measured.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/11368/26911992013-01-01T00:00:00Z