arXiv subjects

S. Moretti

Publications and source records attributed to S. Moretti.

At least 91 records · Page 5Linked to original sources

arXiv2015

LHC phenomenology of light pseudoscalars in the NMSSM

After the discovery of the 125 GeV Higgs boson, the Next-to-Minimal Supersymmetric Standard Model (NMSSM) has become more interesting as a model for new physics since new tree-level contributions to the Higgs mass makes it easier to accommodate the relatively high measured value, as compared to the MSSM. One very distinctive feature of the NMSSM is the possible existence of a light singlet-like pseudoscalar. As this pseudoscalar may be lighter than the discovered Higgs boson without conflict with data, it may lead to LHC signatures rather different to what is usually searched for in terms of new physics. In these proceedings we will discuss studies concerning the discoverability of such light pseudoscalars. It is demonstrated that heavier scalars decaying to pairs of pseudoscalars or pseudoscalars and Z bosons may lead to discovery in a large part of the parameter space. This is especially important for the non-SM like of the two lightest scalars, as it may have an almost 100% branching ratio for decay into pairs of pseudoscalars. In such a case the discussed channels might be our only means of discovery, also for the scalar.

hep-ph↗

arXiv2015

Double Higgs peak in the minimal SUSY B-L model

Motivated by a $\sim 3σ$ excess recorded by the CMS experiment at the LHC around a mass of order $\sim 137$ GeV in $ZZ\to 4l$ and $γγ$ samples, we analyse the discovery potential of a second neutral Higgs boson in the Supersymmetric $B-L$ extension of the Standard Model (BLSSM) at the CERN machine. We confirm that a double Higgs peak structure can be generated in this framework, with CP-even Higgs boson masses at $\sim125$ GeV and $\sim137$ GeV, unlike the case of the Minimal Supersymmetric Standard Model (MSSM).

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arXiv2015

Z'-induced Invisible Right-handed Sneutrino Decays at the LHC

The invisible signals of right-handed sneutrino decays originating from a Z' are analysed at the Large Hadron Collider. The possibility of accessing these events helps disentangling the B-L extension of Minimal Supersymmetric Standard Model from more popular scenarios of Supersymmetry. We assess the scope of the CERN machine in establishing the aforementioned signatures when accompanied by mono-jet, single-photon or Z-radiation probes through sophisticated signal-to-background simulations carried out in presence of parton shower, hadronisation as well as detector effects. We find substantial sensitivity to all such signals for standard luminosities at Run 2.

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arXiv2015

Flavor violating signatures of neutral Higgs bosons at the LHeC

We analyze the prospect for observing the lightest and heaviest CP-even neutral Higgs bosons ($ϕ=h,\;H$) in their decays to flavor violating $b\bar{s}$ (with charge conjugate) final states at the future Large Hadron electron Collider (LHeC), in the framework of the Two Higgs Doublet Model type III (2HDM-III) assuming a four-zero texture in the Yukawa matrices and a general Higgs potential. We consider the charge current production processes $e^- p \to ν_e ϕq_f$ ($ϕ= h, \; H$), with the flavor violating decays of the Higgs bosons. We consider scenarios of the model which are consistent with current experimental data from flavor and Higgs physics. We also consider the most relevant Standard Model (SM) backgrounds. We find that the lightest (SM-like) CP-even Higgs boson $h$ and the heaviest one $ H$ (with mass up to 150 GeV) would have 1--2 $Σ$ and 1 $Σ$ significances, respectively, with 100 fb$^{-1}$ of data. At the end of the LHeC running, the significances would be increased by ten times and the detection of both Higgs bosons ($h, H$) would be guaranteed.

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arXiv2015

XQCAT: eXtra Quark Combined Analysis Tool

XQCAT (eXtra Quark Combined Analysis Tool) is a tool aimed at determining exclusion confidence levels for scenarios of new physics characterised by the presence of one or multiple heavy extra quarks which interact through Yukawa couplings with any of the Standard Model quarks. The code uses a database of efficiencies for pre-simulated processes of QCD-induced pair production of extra quarks and their subsequent on-shell decays. In the version 1.2 of XQCAT the efficiencies have been computed for a set of seven publicly available search results by the CMS experiment. The input for the code is a text file in which masses, branching ratios and dominant chirality of the couplings of the new quarks are provided. The output of the code is the exclusion confidence levels of the test point for each implemented experimental analysis considered individually and, when possible, in statistical combination.

hep-ph↗

arXiv2015

Decays $h\to γγ, \, γZ$ in the Two Higgs Doublet Model Type III

We study the enhancement of the branching ratios of the decays $h \to γγ, \, γZ$ in the Two Higgs Doublet Model Type III, assuming a four-zero Yukawa Texture and a general Higgs potential. We show that these processes are very sensitive to the flavor pattern of the Yukawa texture and the structure of the triple coupling $h H^\pm H^\mp$ from the Higgs potential. We can accomodate the parameters of the model such that one can obtain the $h \toγγ$ rates reported by the LHC and at the same time we can get a $ h \to γZ$ fraction larger than in the SM and within experimental reach. The possibility of obtaining a light charged Higgs boson within the ensuing parameter space and compatible with current experimental measurements is also presented.

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arXiv2015

500 days of Stromgren b, y and narrow-band [OIII], Ha photometric evolution of gamma-ray Nova Del 2013 (= V339 Del)

We present and discuss highly accurate photometry obtained through medium Stromgren y,b bands and narrow [OIII], Halpha bands covering 500 days of the evolution of Nova Del 2013 since its maximum brightness. This is by far the most complete study of any nova observed in such photometric systems. The nova behaviour in these photometric bands is very different from that observed with the more conventional broad bands like UBVRI or ugriz, providing unique information about extent and ionization of the ejecta, the onset of critical phases like the transition between optically thick and thin conditions, and re-ionization by the central super-soft X-ray source. The actual transmission profiles of the y, b, [OIII] and Halpha photometric filters have been accurately measured at different epochs and different illumination angles, to evaluate in detail their performance under exact operating conditions. The extreme smoothness of both the Halpha and [OIII] lightcurves argues for absence of large and abrupt discontinuities in the ejecta of Nova Del 2013. Should they exist, glitches in the lightcurves would have appeared when the ionization and/or recombination fronts overtook them. During the period of recorded very large variability (up to 100x over a single day) in the super-soft X-ray emission (from day +69 to +86 past V maximum), no glitch in excess of 1% was observed in the optical photometry, either in the continuum (Stromgren y) or in the lines ([OIII] and Halpha filters), or in a combination of the two (Stromgren b, Johnson B and V). Considering that the recombination time scale in the ejecta was one week at that time, this excludes global changes of the white dwarf as the source of the X-ray variability and supports instead clumpy ejecta passing through the line of sight to us as its origin.

astro-ph.SR↗

arXiv2015

Higgs boson decays into γγ and Zγ in the MSSM and BLSSM

We calculate Higgs decay rates into γγ and Zγ in the Minimal Supersymmetric Standard Model (MSSM) and (B-L) Supersymmetric Standard Model (BLSSM) by allowing for contributions from light staus and charginos. We show that sizable departures are possible from the SM predictions for the 125 GeV state and that they are testable during run 2 at the Large Hadron Collider. Furthermore, we illustrate how a second light scalar Higgs signal in either or both these decay modes can be accessed at the CERN machine rather promptly within the BLSSM, a possibility instead precluded to the MSSM owing to the much larger mass of its heavy scalar state.

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arXiv2015

$A_{FB}$ as a discovery tool for $Z^\prime$ bosons at the LHC

The Forward-Backward Asymmetry (AFB) in $Z^\prime$ physics is commonly only perceived as the observable which possibly allows one to interpret a $Z^\prime$ signal by distinguishing different models of such (heavy) spin-1 bosons. In this article, we examine the potential of AFB in setting bounds on or even discovering a $Z^\prime$ at the Large Hadron Collider (LHC) and show that it might be a powerful tool for this purpose. We analyze two different scenarios: $Z^\prime$s with a narrow and wide width, respectively. We find that in both cases AFB can complement the cross section in accessing $Z^\prime$ signals.

hep-ph↗

arXiv2015

Forward-Backward Asymmetry as a Discovery Tool for Z' Bosons at the LHC

The Forward-Backward Asymmetry (AFB) in Z' physics is commonly only perceived as the observable which possibly allows one to interpret a Z' signal by distinguishing different models of such (heavy) spin-1 bosons. In this paper, we examine the potential of AFB in setting bounds on or even discovering a Z' boson at the Large Hadron Collider (LHC) and show that it might be a powerful tool for this purpose. We analyse two different scenarios: Z' bosons with a narrow and wide width, respectively. We find that, in the first case, the significance of the AFB search can be comparable with that of the bump search usually adopted by the experimental collaborations; however, being a ratio of (differential) cross sections the AFB has the advantage of reducing systematical errors. In the second case, the AFB search can win over the bump search in terms of event shape, as the structure of the AFB distribution as a function of the invariant mass of the reconstructed Z'boson could nail down the new broad resonance much better than the event counting strategy usually adopted in such cases.

hep-ph↗

arXiv2015

Analysis of the quark sector in the 2HDM-III with a four-zero Yukawa texture using the most recent data on the CKM matrix

In this letter we analyse, in the context of the general 2-Higgs Doublet Model, the structure of the Yukawa matrices, $\widetilde{ \bf Y}_{ _{1,2} }^{q}$, by assuming a four-zero texture ansatz for their definition. In this framework, we obtain compact expressions for $\widetilde{ \bf Y}_{ _{1,2} }^{q}$, which are reduced to the Cheng and Sher ansatz with the difference that they are obtained naturally as a direct consequence of the invariants of the fermion mass matrices. Furthermore, in order to avoid large flavour violating effects coming from charged Higgs exchange, we consider the main flavour constraints on the off-diagonal terms of Yukawa texture {{$\left( \widetildeχ_{j}^q \right)_{kl}$}} ($k\neq l$). We perform a $χ^2$-fit based on current experimental data on the quark masses and the Cabibbo-Kobayashi-Maskawa mixing matrix ${ \bf V}_{\rm CKM }$. Hence, we obtain the allowed ranges for the parameters $\widetilde{ \bf Y}_{ _{1,2} }^{q}$ at 1$σ$ for several values of $\tan β$. The results are in complete agreement with the bounds obtained taking into account constraints on Flavour Changing Neutral Currents reported in the literature.

hep-ph↗

arXiv2015

Unitarity in composite Higgs approaches with vector resonances

We examine a simple Composite Higgs Model (CHM) with vector resonances in addition to the Standard Model (SM) fields in perturbation theory by using the $K$-matrix method to implement unitarity constraints. We find that the $W_LW_L$ scattering amplitude has an additional scalar pole (analogous to the $σ$ meson of QCD) as in generic strongly interacting extensions of the SM. The mass and width of this dynamically generated scalar resonance are large and the mass behaves contrary to the vector one, so that when the vector resonance is lighter, the scalar one is heavier, and vice versa. We also attempt an interpretation of this new resonance. Altogether, the presence of the vector state with the symmetries of the CHM improve the low-energy unitarity behavior also in the scalar-isoscalar channel.

hep-ph↗

arXiv2014

Framework for Model Independent Analyses of Multiple Extra Quark Scenarios

In this paper we present an analysis strategy and a dedicated tool to determine the exclusion confidence level for any scenario involving multiple heavy extra quarks with generic decay channels, as predicted in several extensions of the Standard Model. We have created, validated and used a software package, called XQCAT (eXtra Quark Combined Analysis Tool), which is based on publicly available experimental data from direct searches for top partners and from Supersymmetry inspired searches. By means of this code, we recast the limits from CMS on new heavy extra quarks considering a complete set of decay channels. The resulting exclusion confidence levels are presented for some simple scenarios with multiple states and general coupling assumptions. Highlighting the importance of combining multiple topology searches to obtain accurate re-interpretations of the existing searches, we discuss the reach of the SUSY analyses so as to set bounds on new quark resonances. In particular, we report on the re-interpretation of the existing limits on benchmark scenarios with one and multiple pair-produced top partners having non-exclusive couplings to the third Standard Model generation of quarks.

hep-ph↗

arXiv2014

$H^\pm\to cb$ in models with two or more Higgs doublets

Searches for light $H^\pm$s via $t\to H^\pm b$ are being carried out at the LHC. Herein, it is normally assumed that the dominant decay channels are $H^\pm\to τν$ and $H^\pm\to cs$ and separate data analyses are performed with comparable sensitivity to the underlying model assumptions. However, the $H^\pm\to cb$ decay rate can be as large as $80\%$ in models with two or more Higgs doublets with natural flavour conservation, while satisfying the constraint from $b\to sγ$ for $m_{H^\pm}< m_t$. Despite the current search strategy for $H^\pm\to cs$ is also sensitive to $H^\pm\to cb$, a significant gain in sensitivity could be obtained by tagging the $b$ quark from the decay $H^\pm\to cb$.

hep-ph↗

arXiv2014

Multiple Z' -> t-tbar signals in a 4D Composite Higgs Model

We study the production of top-antitop pairs at the Large Hadron Collider as a testbed for discovering heavy Z' bosons belonging to a composite Higgs model, as, in this scenario, such new gauge interaction states are sizeably coupled to the third generation quarks of the Standard Model. We study their possible appearance in cross section as well as (charge and spin) asymmetry distributions. Our calculations are performed in the minimal four-dimensional formulation of such a scenario, namely the 4-Dimensional Composite Higgs Model (4DCHM), which embeds five new $Z'$s. We pay particular attention to the case of nearly degenerate resonances, highlighting the conditions under which these are separable in the aforementioned observables. We also discuss the impact of the intrinsic width of the new resonances onto the event rates and various distributions. We confirm that the 14 TeV stage of the LHC will enable one to detect two such states, assuming standard detector performance and machine luminosity. A mapping of the discovery potential of the LHC of these new gauge bosons is given. Finally, from the latter, several benchmarks are extracted which are amenable to experimental investigation.

hep-ph↗

arXiv2014

Composite Higgs searches at the LHC and beyond

General Composite Higgs models provide an elegant solution to the hierarchy problem present in the Standard Model and give an alternative pattern leading to the mechanism of electroweak (EW) symmetry breaking. We present an analysis of a realistic realization of this general idea, namely the 4DCHM, analysing the Higgs production and decay modes, fitting them to the latest LHC showing the compatibility with the results of the CERN machine. We then present the prospects of a future electron positron collider of testing this model against the expected experimental accuracies in the various Higgs decay channels accessible herein.

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arXiv2014

Variations on a Higgs theme

We show how the $Z$ boson can be generated in gluon-gluon fusion and yield two photons, via $gg\to Z\to γγ$, through massive fermion loops only, thereby contributing events to a candidate Higgs sample in the di-photon channel. A sub-leading contribution also exists from $q\bar q\to Z\toγγ$ events. Assuming the Standard Model, the corresponding event rates are negligible at the LHC stages of 7, 8 TeV, given the luminosities collected therein (about 5 and 20 fb$^{-1}$, respectively). Conversely, at 14 TeV, the first process become accessible for luminosities of order 300 fb$^{-1}$. Finally, we show how additional fermion states entering such loops, in production, in decay or in both cases, could affect the predictions in this channel by curiously mimicking Higgs signals.

hep-ph↗

arXiv2014

Impact of a four-zero Yukawa texture on $h\to γγ$ and $γZ$ in the framework of the Two Higgs Doublet Model Type III

We study the substantial enhancement, with respect to the corresponding Standard Model rates, that can be obtained for the branching ratios of the decay channels $h \to γγ$ and $h\to γZ$ within the framework of the Two Higgs Doublet Model Type III, assuming a four-zero Yukawa texture and a general Higgs potential. We show that these processes are very sensitive to the flavor pattern entering the Yukawa texture and to the triple coupling structure of the Higgs potential, both of which impact onto the aforementioned decays. We can accommodate the parameters of the model in such a way to obtain the $h \to γγ$ rates reported by the Large Hadron Collider and at the same time we get a $h\to γZ$ fraction much larger than in the Standard Model, indeed within experimental reach. We present some scenarios where this phenomenology is realized for spectrum configurations that are consistent with current constraints. We also discuss the possibility of obtaining a light charged Higgs boson compatible with all such measurements, thereby serving the purpose of providing a hallmark signal of the scenario considered.

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