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S. Moretti

Publications and source records attributed to S. Moretti.

At least 163 records · Page 9Linked to original sources
arXiv2009

The Constrained Exceptional Supersymmetric Standard Model

We propose and study a constrained version of the Exceptional Supersymmetric Standard Model (E6SSM), which we call the cE6SSM, based on a universal high energy scalar mass m_0, trilinear scalar coupling A_0 and gaugino mass M_{1/2}. We derive the Renormalisation Group (RG) Equations for the cE6SSM, including the extra U(1)_{N} gauge factor and the low energy matter content involving three 27 representations of E6. We perform a numerical RG analysis for the cE6SSM, imposing the usual low energy experimental constraints and successful Electro-Weak Symmetry Breaking (EWSB). Our analysis reveals that the sparticle spectrum of the cE6SSM involves a light gluino, two light neutralinos and a light chargino. Furthermore, although the squarks, sleptons and Z' boson are typically heavy, the exotic quarks and squarks can also be relatively light. We finally specify a set of benchmark points which correspond to particle spectra, production modes and decay patterns peculiar to the cE6SSM, altogether leading to spectacular new physics signals at the Large Hadron Collider (LHC).

hep-ph↗
arXiv2009

Full One-loop Electro-Weak Corrections to Three-jet Observables at the Z pole and Beyond

We describe the impact of the full one-loop EW terms of O(alpha_s alpha_EM^3) entering the electron-positron into three-jet cross-section from \sqrt{s}=M_Z to TeV scale energies. We include both factorisable and non-factorisable virtual corrections, photon bremsstrahlung but not the real emission of W and Z bosons. Their importance for the measurement of alpha_S from jet rates and shape variables is explained qualitatively and illustrated quantitatively.

hep-ph↗
arXiv2009

Yukawa txtures and charged Higgs boson phenomenology in the type-III two-Higgs-doublet model

We discuss the implications of assuming a four-zero Yukawa texture for the properties of the charged Higgs boson within the context of the general 2-Higgs Doublet Model of Type III. We begin by presenting a detailed analysis of the charged Higgs boson couplings with heavy quarks and the resulting pattern for its decays. The production of charged Higgs bosons is also sensitive to the modifications of its couplings, so that we also evaluate the resulting effects on the top decay $t \to b H^{+}$ as well as on `direct' $c\bar{b}\to H^++c. c.$ and `indirect' $q\bar q,gg\to \bar t b H^++c. c.$ production. Significant scope exists at the Large Hadron Collider for several $H^\pm$ production and decay channels combined to enable one to distinguish between such a model and alternative 2-Higgs doublet scenarios.

hep-ph↗
arXiv2009

One-loop Electro-Weak Corrections to the Event Orientation of e+e- into 3 jet Processes

We compute the full one-loop Electro-Weak (EW) contributions of O(alpha_S alpha_EM^3) entering the electron-positron into a quark-antiquark pair plus one gluon cross section at the Z peak and LC energies in presence of polarisation of the initial state and by retaining the event orientation of the final state. We include both factorisable and non-factorisable virtual corrections, photon bremsstrahlung but not the real emission of W^\pm and Z bosons. Their importance for the final state orientation is illustrated for beam polarisation setups achieved at SLC and foreseen at ILC and CLIC.

hep-ph↗
arXiv2009

StHa 55: a carbon Mira, not a symbiotic binary

We carried out a VRI photometric monitoring of StHa 55, and in addition we obtained low resolution absolute spectro-photometry and high resolution Echelle spectroscopy. Our data show that StHa 55 is a carbon Mira, pulsating with a 395 day period, with =13.1 mean brightness and 2.8 mag amplitude in V band. It suffers from a low reddening (E(B-V)=0.15), lies at a distance of 5 kpc from the Sun and 1 kpc from the galactic plane, and its heliocentric systemic velocity is close to +22 km/sec. The difference between the radial velocity of the optical absorption spectrum and that of the Ha emission is unusually small for a carbon Mira. The spectrum of StHa 55 can be classified as C-N5 C2 6-. Its 13C/12C isotopic ratio is normal, and lines of BaII and other s-type elements, as well as LiI, have the same intensity as in field carbon stars of similar spectral type. The Balmer emission lines are very sharp and unlike those seen in symbiotic binaries. Their intensity changes in phase with the pulsation cycles in the same way as seen in field carbon Miras. We therefore conclude that StH 55 is a bona fide, normal carbon Mira showing no feature supporting a symbiotic binary classification, as previously hypothesized.

astro-ph.SR↗
arXiv2009

Higgs Production in Association with Top Squark Pairs in the MSSM at the LHC: the Decay Patterns

The production of the lightest Higgs boson, $h^0$, in association with the lightest stop, $\tilde{t}_{1}$, in the Minimal Supersymmetric Standard Model, is an interesting channel, as its cross section can be higher than Higgs production in association with top quarks. Furthermore, the $\tilde{t}_{1}\tilde{t}^{*}_{1}h^{0}$ production rate is highly dependent on various Supersymmetric parameters. The mass, mixings, couplings and production cross sections relevant to the $\tilde{t}_{1}\tilde{t}^{*}_{1}h^{0}$ channel have been studied in the past. Here, we complement these analyses by performing a thorough decay study. We conclude that there is some scope for extracting this channel at the Large Hadron Collider, for suitable combinations of the Supersymmetric parameters, in several different decay channels of both the stop quarks and Higgs boson, the most numerically promising being the signature involving charm decays of the stops and bottom decay of the Higgs. This, in fact, remains true in the Supergravity inspired Minimal Supersymmetric Standard Model.

hep-ph↗
arXiv2008

One-loop Electro-Weak Corrections to Three-jet Observables of b-quarks in e+e- Annihilations

We compute the full one-loop EW contributions of O(α_S alpha_EM^3) entering the electron-positron into two b-quarks and one gluon cross section at the Z peak and LC energies. We include both factorisable and non-factorisable virtual corrections, photon bremsstrahlung but not the real emission of W^\pm and Z bosons. Their importance for the measurement of alpha_S from jet rates and shape variables is explained qualitatively and illustrated quantitatively. Their impact on the forward-backward asymmetry is also analysed.

hep-ph↗
arXiv2008

The Constrained E$_6$SSM

We present a self--consistent $E_6$ inspired supersymmetric model with an extra $U(1)_{N}$ gauge symmetry under which right-handed neutrinos have zero charge. We explore the particle spectrum within the constrained version of this exceptional supersymmetric standard model (E$_6$SSM) and discuss its possible collider signatures.

hep-ph↗
arXiv2008

The nature and evolution of Nova Cygni 2006

AIMS: Nova Cyg 2006 has been intensively observed throughout its full outburst. We investigate the energetics and evolution of the central source and of the expanding ejecta, their chemical abundances and ionization structure, and the formation of dust. METHOD: We recorded low, medium, and/or high-resolution spectra (calibrated into accurate absolute fluxes) on 39 nights, along with 2353 photometric UBVRcIc measures on 313 nights, and complemented them with IR data from the literature. RESULTS: The nova displayed initially the normal photometric and spectroscopic evolution of a fast nova of the FeII-type. Pre-maximum, principal, diffuse-enhanced, and Orion absorption systems developed in a normal way. After the initial outburst, the nova progressively slowed its fading pace until the decline reversed and a second maximum was reached (eight months later), accompanied by large spectroscopic changes. Following the rapid decline from second maximum, the nova finally entered the nebular phase and formed optically thin dust. We computed the amount of formed dust and performed a photo-ionization analysis of the emission-line spectrum during the nebular phase, which showed a strong enrichment of the ejecta in nitrogen and oxygen, and none in neon, in agreement with theoretical predictions for the estimated 1.0 Msun white dwarf in Nova Cyg 2006. The similarities with the poorly investigated V1493 Nova Aql 1999a are discussed.

astro-ph↗
arXiv2008

Lepton Flavour Violating Heavy Higgs Decays Within the nuMSSM and Their Detection at the LHC

Within the $ν$MSSM, a Minimal Supersymmetric neutrino See-saw Model, Lepton Flavour Violating Higgs couplings are strongly enhanced at large $\tanβ$ ($\gsim30$), which can lead to BR$(H^0/A^0 \to τμ) \simeq O(10^{-4})$, for $M_{H^0/A^0}\gsim 160$ GeV. Enhancements on the production of Higgs bosons, through the gluon fusion mechanism, $gg\to H^0/A^0$, and the associated production channel $gg,q\bar q\to b\bar bH^0/A^0$, whose rates grow with $\tanβ$, as well as the mass degeneracy that occurs between the $H^0$ and $A^0$ states in this regime, also contribute to further the possibilities to detect a heavy Higgs signal into $τμ$ pairs. We show that the separation of $τμ$ Higgs events from the background at the upcoming CERN Large Hadron Collider could be done for Higgs masses up to about 600 GeV for 300 fb$^{-1}$ of luminosity, for large $\tanβ$ values. However, even with as little as 10 fb$^{-1}$ one can probe $H^0/A^0$ masses up to 400 GeV or so, if $\tanβ=60$. Altogether, these processes then provide a new Higgs discovery mode as well as an independent test of flavour physics.

hep-ph↗
arXiv2008

One-loop electroweak corrections to e+e- into three-jets

We describe the impact of the full one-loop Electro-Weak terms of O($α_sα^3_{EM}$) entering the electron-positron into three-jet cross-section. We include both factorisable and non-factorisable virtual corrections, photon bremsstrahlung but not the real emission of $W^\pm$ and $Z$ bosons. We show preliminary results and we discuss the impact of the Electro-Weak corrections on three-jet observables.

hep-ph↗
arXiv2008

Benchmark scenarios for the NMSSM

We discuss constrained and semi--constrained versions of the next--to--minimal supersymmetric extension of the Standard Model (NMSSM) in which a singlet Higgs superfield is added to the two doublet superfields that are present in the minimal extension (MSSM). This leads to a richer Higgs and neutralino spectrum and allows for many interesting phenomena that are not present in the MSSM. In particular, light Higgs particles are still allowed by current constraints and could appear as decay products of the heavier Higgs states, rendering their search rather difficult at the LHC. We propose benchmark scenarios which address the new phenomenological features, consistent with present constraints from colliders and with the dark matter relic density, and with (semi--)universal soft terms at the GUT scale. We present the corresponding spectra for the Higgs particles, their couplings to gauge bosons and fermions and their most important decay branching ratios. A brief survey of the search strategies for these states at the LHC is given.

hep-ph↗
arXiv2008

Studies of Spin Effects in Charged Higgs Boson Production with an Iterative Discriminant Analysis at the Tevatron and LHC

We report on detailed Monte Carlo comparisons of selection variables to separate tbH+ signal events from the Standard Model ttbar background using an Iterative Discriminant Analysis (IDA) method. While kinematic differences exist between the two processes whenever m(H+).ne.m(W+), the exploration of the spin difference between the charged Higgs and the W+ gauge boson becomes crucial in the particularly challenging case of near degeneracy of the charged Higgs boson mass with the W+ mass. The TAUOLA package is used to decay the tau leptons emerging from the charged Higgs and W+ boson decays taking the spin difference properly into account. We demonstrate that, even if the individual selection variables have limited discriminant power, the IDA method achieves a significant separation between the expected signal and background. For both Tevatron and LHC energies, the impact of the spin effects and H+ mass on the separation of signal and background has been studied quantitatively. The effect of a hard transverse momentum cut to remove QCD background has been studied and it is found that the spin effects remain important. The separation is expressed in purity versus efficiency curves. The study is performed for charged Higgs boson masses between the W+ mass and near the top mass.

hep-ph↗
arXiv2008

Charged Higgs boson phenomenology in Supersymmetric models with Higgs triplets

We present a detailed study of the Higgs sector within an extension of the Minimal Supersymmetric Standard Model that includes one Complex Higgs Triplet (MSSM+1CHT). The model spectrum includes three singly charged Higgs bosons as well as three CP-even (or scalar) and two CP-odd (or pseudoscalar) neutral Higgs bosons. We present an approximated calculation of the one-loop radiative corrections to the neutral CP-even Higgs masses ($m_{H_i^0}$) and the couplings $H_i^0 Z^0 Z^0$ ($i=1$, 2, 3), which determine the magnitude of the Higgs-strahlung processes $e^+ e^-\to Z^0 H^0_i$. Limits from LEP2 are then considered, in order to obtain bounds on the neutral Higgs sector. Further, we also include the experimental limits from LEP2 on $e^+e^-\to H^+H^-$ and those on BR($t \to b H^+$) from Tevatron, to derive bounds on the mass of the two lightest charged Higgs bosons ($H_1^{\pm}$ and $H_2^{\pm}$). Concerning the latter, we find some cases, where $m_{H_1^{\pm}} \simeq 90$ GeV, that are not excluded by any experimental bound, even for large values of $\tanβ$, so that they should be looked for at the Large Hadron Collider (LHC).

hep-ph↗
arXiv2007

Tevatron-for-LHC Report: Higgs

The search for Higgs bosons in both the standard model and its extensions is well under way at the Tevatron. As the integrated luminosity collected increases into the multiple inverse femptobarn range, these searches are becoming very interesting indeed. Meanwhile, the construction of the Large Hadron Collider (LHC) and its associated experiments at CERN are nearing completion. In this TeV4LHC workshop, it was realized that any experience at the Tevatron with respect to backgrounds, experimental techniques and theoretical calculations that can be verified at the Tevatron which have relevance for future measurements at the LHC were important. Studies and contributions to these efforts were made in three broad categories: theoretical calculations of Higgs production and decay mechanisms; theoretical calculations and discussions pertaining to non-standard model Higgs bosons; and experimental reviews, analyses and developments at both the Tevatron and the upcoming LHC experiments. All of these contributions represent real progress towards the elucidation of the mechanism of electroweak symmetry breaking.

hep-ph↗
arXiv2007

Di-photon Higgs Decay in SUSY with CP Violation

Physical Higgs particles in the Minimal Supersymmetric Standard Model (MSSM) with explicit CP violation are CP mixed states. The decay of these Higgs particles can be analysed to study the CP properties of the MSSM. In the present work we consider the di-photon channel of the lightest neutral Higgs boson for this purpose. Compared to earlier studies on effects of scalar/pseudo-scalar mixing, our analysis also investigates the effect due to Higgs-sfermion-sfermion couplings along with that of mixing. We find that a light stop may have a strong impact on the width and Branching Ratio (BR) of the decay process H1 --> gamma.gamma, whereas other light sparticles have only little influence. In some regions of the MSSM parameter space with large CP-violating phase phi-mu ~ 90 deg a light (~ 200 GeV) stop can change the di-photon BR by more than 50 % compared to the case with heavy (~ 1 TeV) stop and otherwise same MSSM parameters.

hep-ph↗