arXiv subjects

S. Moretti

Publications and source records attributed to S. Moretti.

At least 55 records · Page 3Linked to original sources

arXiv2021

Below-threshold CP-odd Higgs boson search via A -> Z* h at the LHC

We study the process q q, g g -> A -> Z* h in a 2-Higgs Doublet Model Type-II where the mass of the CP-odd Higgs state A is lower than the rest mass of the Z and h particles (the latter being the Standard Model-like Higgs state), i.e., mA < mZ + mh = 215 GeV. This is a mass range which is not being currently tested by ATLAS and CMS in this channel, yet we show that there can be sensitivity to it already during Runs 2 and 3, assuming leptonic decays of the gauge boson and bottom-antibottom quark ones for the Higgs boson.

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arXiv2021

Analysis of $W^\pm+4γ$ in the 2HDM Type-I at the LHC

We analyse a light charged Higgs boson in the 2-Higgs Doublet Model (2HDM) Type-I, when its mass satisfies the condition $M_{H^{\pm}} < M_{t}+M_{b}$ and the parameter space is consistent with theoretical requirements of self-consistency as well as the latest experimental constraints from Large Hadron Collider (LHC) and other data. Over such a parameter space, wherein the Standard Model (SM)-like state discovered at the LHC in 2012 is the heaviest CP-even state of the 2HDM, it is found that the decay modes of the charged Higgs boson are dominated by $H^{\pm} \rightarrow W^{\pm *} h$. Furthermore, the light neutral Higgs boson $h$ dominantly decays into two photons. Under these conditions, we find that the production and decay process $ p p \to H^\pm h \to {W^\pm}^{(*)} h h \to l ν_{l} + 4 γ$ ($l=e,μ$) is essentially background free. However, since the $W^{\pm(*)}$ could be largely off-shell and the $h$ state is very light, so that both the lepton coming from the former and the photons coming from the latter could be rather soft, we perform here a full Monte Carlo (MC) analysis at the detector level demonstrating that such a $W^{\pm} + 4γ$ signal is very promising, as it would be yielding significant excesses at the LHC with an integrated luminosity of $L=$ 300 $fb^{-1}$ at both $\sqrt{s}= 13$ and $14 ~\text{TeV}$.

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arXiv2021

The $Z_3$ symmetric I(2+1)HDM

We introduce a 3-Higgs Doublet Model (3HDM) with two Inert (or dark) scalar doublets and an active Higgs one, hence termed I(2+1)HDM, in the presence of a discrete $Z_3$ symmetry acting upon the three doublet fields. We show that such a construct yields a Dark Matter (DM) sector with two mass-degenerate states of opposite CP parity, both of which contribute to DM dynamics, which we call \textit{Hermaphrodite DM}, distinguishable from a (single) complex DM candidate. We show that the relic density contributions of both states are equal, saturating the observed relic density compliant with (in)direct searches for DM as well as other experimental data impinging on both the dark and Higgs sectors of the model, chiefly, in the form of Electro-Weak Precision Observables (EWPOs), Standard Model (SM)-like Higgs boson measurements at the Large Hadron Collider (LHC) and void searches for additional (pseudo)scalar states at the CERN machine and previous colliders.

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arXiv2020

Complementary Probes of Two-component Dark Matter

We study a $Z_2 \times Z'_2$ symmetric 3-Higgs Doublet Model (3HDM), wherein two of the doublets are inert and one is active (thus denoted in literature as I(2+1)HDM), yielding a two-component Dark Matter (DM) sector. The two DM candidates emerge as the lightest scalar component of a different inert doublet, each with a different odd discrete parity, and cooperate to achieve the correct relic density. When a sufficient mass difference exists between the two DM candidates, it is possible to test the presence of both in present and/or forthcoming facilities, as the corresponding masses are typically at the electroweak scale. Specifically, the light DM component can be probed by the nuclear recoil energy in direct detection experiments while the heavy DM component appears through the photon flux in indirect detection experiments. In fact, the DM mass sensitivity that the two experimental set-ups can achieve should be adequate to establish the presence of two different DM signals. This result has been obtained in the presence of a thorough theoretical analysis of the stability conditions of the vacuum structure emerging from our I(2+1)HDM construct, ensuring that the model configurations adopted are physical, and of up-to-date constraints coming from data collected by both space and ground experiments, ensuring that the coupling and mass spectra investigated are viable phenomenologically.

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arXiv2020

Charged Higgs boson production via $cb-$fusion at the Large Hadron Collider

We analyse the production of a light charged Higgs boson at the Large Hadron Collider (LHC) via the quark-fusion mechanism $c \bar{b} \to H^- $ considering the decay channel $H^- \to τ\bar ν_τ$ in the final state. We study this process in the framework of the 2-Higgs Doublet Model Type III (2HDM-III) which assumes a four-zero texture in the Yukawa matrices and a general Higgs potential, wherein the two Higgs doublets coupling to both up and down fermions do generate Flavour Changing Neutral Currents (FCNCs) yet the latter can be controlled by the texture when flavour physics constraints are considered. We consider the parameter space of the model where this signal is enhanced and in agreement with both theoretical constraints and experimental data. In particular, we exploit the setup with lepton-specific-like Yukawa couplings and assess the LHC sensitivity to such $H^\pm$ signals against the dominant {irreducible and} reducible backgrounds. We show that in our model BR$(H^\pm \to cb) \sim 0.1- 0.2$ and BR$(H^\pm \to τν) \sim 0.7-0.9$ so that, under these conditions, the prospects for $H^\pm$ detection in the 2HDM-III in the aforementioned production and decay channels are excellent assuming standard collider energy and luminosity conditions.

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arXiv2020

The sustained post-outburst brightness of Nova Per 2018, the evolved companion, and the long orbital period

Nova Per 2018 (= V392 Per) halted the decline from maximum when it was 2mag brighter than quiescence and since 2019 has been stable at such a plateau. The ejecta have already fully diluted into the interstellar space. We obtained BVRIgrizY photometry and optical spectroscopy of V392 Per during the plateau phase and compared it with equivalent data gathered prior to the nova outburst. We find the companion star to be a G9 IV/III and the orbital period to be 3.4118 days, making V392 Per the longest known period for a classical nova. The location of V392 Per on the theoretical isochrones is intermediate between that of classical novae and novae erupting within symbiotic binaries, in a sense bridging the gap. The reddening is derived to be E(B-V)=0.72 and the fitting to isochrones returns a 3.6 Gyr age for the system and 1.35 Msun, 5.3 Rsun, and 15 Lsun for the companion. The huge Ne overabundance in the ejecta and the very fast decline from nova maximum both point to a massive white dwarf (M(WD) >= 1.1-1.2 Msun). The system is viewed close to pole-on conditions and the current plateau phase is caused by irradiation of the CS by the WD still burning at the surface.

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arXiv2020

Alleviating the $\bar B \to D τν$ and $\bar B \to D^* τν_τ$ puzzle in the MSSM

We show that Supersymmetric effects driven by penguin contributions to the $b \to c τν_τ$ transition are able to account simultaneously for a sizeable increase of both branching ratios of $\bar{B}\to D τ\barν_τ$ and $\bar{B} \to D^{*} τ\barν_τ$ with respect to the Standard Model predictions, thereby approaching their experimentally measured values. We emphasise that a light chargino and neutralino, with masses less than 300 GeV, in addition to a large stau/snueutrino mass and a large $\tanβ$, are essential for enhancing the effect of the lepton penguin $τν_τW^{\pm}$, which is responsible for the improved theoretical predictions with respect to current data.

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arXiv2020

Lepton collider signatures of dark CP violation

We study an extension of the Standard Model (SM) in which two copies of the SM Higgs doublet are added to the scalar sector. These extra doublets do not develop a vacuum expectation value, hence, they are \textit{inert}. This essentially leads to a 3-Higgs Doublet Model (3HDM) with 2 inert and 1 active scalar doublets, which we denote as I(2+1)HDM. We allow for CP-violation in the \textit{inert} sector, where the lightest \textit{inert} state is protected from decaying to SM particles through the conservation of a $Z_2$ symmetry, so that it is a Dark Matter (DM) candidate. For this scenario, we identify a smoking gun signature of dark CP-violation in the form of production thresholds of pairs of \textit{inert} neutral Higgs bosons at an $e^+e^-$ collider.

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arXiv2020

Collider signatures of dark CP-violation

We study an extension of the Standard Model (SM) in which two copies of the SM-Higgs doublet which do not acquire a vacuum expectation value, and hence are {\it inert}, are added to the scalar sector. The lightest particle from the inert sector, which is protected from decaying to SM particles through the conservation of a $Z_2$ symmetry, is a viable dark matter candidate. We allow for CP-violation in this extended dark sector and evaluate the $ZZZ$ vertex and its CP-violating form factor in several benchmark scenarios. We provide collider signatures of this dark CP-violation in the form of potentially observable asymmetries and cross sections for the $f\bar f\to Z^*\to ZZ$ process at both leptonic and hadronic machines.

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arXiv2020

A Review of the Exceptional Supersymmetric Standard Model

Local supersymmetry (SUSY) provides an attractive framework for the incorporation of gravity and unification of gauge interactions within Grand Unified Theories (GUTs). Its breakdown can lead to a variety of models with softly broken SUSY at low energies. In this review article we focus on the SUSY extension of the Standard Model (SM) with an extra U(1)_{N} gauge symmetry originating from a string-inspired E_6 grand unified gauge group. Only in this U(1) extension of the minimal supersymmetric standard model (MSSM) inspired by E_6 GUTs the right-handed neutrinos can be superheavy providing a mechanism for the generation of the lepton and baryon asymmetry of the Universe. The particle content of this exceptional supersymmetric standard model (E_6SSM) includes three 27 representations of the E_6 group, to ensure anomaly cancellation, plus a pair of SU(2)_W doublets as required for gauge coupling unification. Thus E_6SSM involves extra exotic matter beyond the MSSM. We consider symmetries that permit to suppress non-diagonal flavour transitions and rapid proton decay, as well as gauge coupling unification, the breakdown of the gauge symmetry and the spectrum of Higgs bosons in this model. The possible Large Hadron Collider (LHC) signatures caused by the presence of exotic states are also discussed.

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arXiv2019

Dark Matter Spin Characterisation in Mono-$Z$ Channels

The $B-L$ Supersymmetric Standard Model (BLSSM) is an ideal testing ground of the spin nature of Dark Matter (DM) as it offers amongst its candidates both a spin-1/2 (the lightest neutralino) and spin-0 (the lightest right-handed sneutrino) state. We show that the mono-$Z$ channel can be used at the Large Hadron Collider (LHC) to diagnose whether a DM signal is characterised within the BLSSM by a fermionic or (pseudo)scalar DM particle. Sensitivity to either hypothesis can be obtained after only 100 fb$^{-1}$ of luminosity following Runs 2 and 3 of the LHC.

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arXiv2019

Production of Z'-Boson Resonances with Large Width at the LHC

Di-lepton searches for Beyond the Standard Model (BSM) Z' bosons that rely on the analysis of the Breit-Wigner (BW) line shape are appropriate in the case of narrow resonances, but likely not sufficient in scenarios featuring Z' states with large widths. Conversely, alternative experimental strategies applicable to wide Z' resonances are much more dependent than the default bump search analyses on the modelling of QCD higher-order corrections to the production processes, for both signal and background. For heavy Z' boson searches in the di-lepton channel at the CERN Large Hadron Collider (LHC), the transverse momentum q_T of the di-lepton system peaks at q_T \ltap 10^{-2} M_{ll}, where M_{ll} is the di-lepton invariant mass. We exploit this to treat the QCD corrections by using the logarithmic resummation methods in M_{ll} / q_T to all orders in the strong coupling constant α_s. We carry out studies of Z' states with large width at the LHC by employing the program {\tt reSolve}, which performs QCD transverse momentum resummation up to Next-to-Next-to-Leading Logarithmic (NNLL) accuracy. We consider two benchmark BSM scenarios, based on the Sequential Standard Model (SSM) and dubbed `SSM wide' and `SSM enhanced'. We present results for the shape and size of Z' boson signals at the differential level, mapped in both cross section (σ) and Forward-Backward Asymmetry (A_{\rm FB}), and perform numerical investigations of the experimental sensitivity at the LHC Run 3 and High-Luminosity LHC (HL-LHC).

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arXiv2019

Light charged Higgs boson production at future $ep$ colliders

We present a recent study of light charged Higgs boson ($H^-$) production at the Large Hadron electron Collider (LHeC). We study the charged current production process $e^- p \to ν_e q H^-$, taking in account the decay channels $H^- \to b\bar{c}$ and $H^-\to τ\barν_τ$. We analyse the process in the framework of the 2-Higgs Doublet Model Type-III (2HDM-III), assuming a four-zero texture in the Yukawa matrices and a general Higgs potential. We consider a variety of both reducible and irreducible backgrounds for the signals of the $H^-$ state. We show that the detection of a light charged Higgs boson is feasible, assuming for the LHeC standard energy and luminosity conditions.

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arXiv2019

Light charged Higgs boson production at the Large Hadron electron Collider

We study the production of a light charged Higgs boson at the future Large Hadron electron Collider (LHeC), through the process $e^- p \to ν_e H^- q$ considering both decay channels $H^- \to b \bar c$ and $H^- \to τ\bar ν_τ$ in the final state. We analyse these processes in the context of the 2-Higgs Doublet Model Type III (2HDM-III) and assess the LHeC sensitivity to such $H^-$ signals against a variety of both reducible and irreducible backgrounds. We confirm that prospects for $H^-$ detection in the 2HDM-III are excellent assuming standard collider energy and luminosity conditions.

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arXiv2019

Constraining Parton Distribution Functions from Neutral Current Drell-Yan Measurements

We study the cross section σand Forward-Backward asymmetry A_{FB} in the process pp \to γ^*,Z \to \ell^+\ell^- (with \ell=e,μ) for determinations of Parton Distribution Functions (PDFs) of the proton. We show that, once mapped in the invariant mass of the di-lepton final state, M({\ell\ell}), both observables, σand A_{FB}, display a statistical error which is presently competitive with that assigned to the existing PDF sets and which will rapidly become smaller than the latter as the luminosity being accumulated at Run-II of the LHC grows. This statement is applicable to both on-peak and off-peak M({\ell\ell}) regions, both (just) below and above it, thereby offering a means of constraining the quark PDFs over a sizeable (x,Q^2) range.

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arXiv2019

Advancing LHC Probes of Dark Matter from the Inert 2-Higgs Doublet Model with the Mono-jet Signal

The inert 2-Higgs Doublet Model (i2HDM) is a well-motivated minimal consistent Dark Matter (DM) model, but it is rather challenging to test at the Large Hadron Collider (LHC) in the parameter space allowed by relic density and DM direct detection constraints. This is especially true when considering the latest XENON 1T data on direct DM searches which we use here to present the best current combined limit on the i2HDM parameter space. In this analysis, we present prospects to advance the exploitation of DM mono-jet signatures from the i2HDM at the LHC, by emphasising that a shape analysis of the missing transverse momentum distribution allows one to sizably improve the LHC discovery potential. As a key element of our analysis, we explore the validity of using an effective vertex, $ggH$, for the coupling of the Higgs boson to gluons using a full one-loop computation. We have found sizeable differences between the two approaches, especially in the high missing transverse momentum region, and incorporated the respective K-factors to obtain the correct kinematical distributions. As a result, we delineate a realistic search strategy and present the improved current and projected LHC sensitivity to the i2HDM parameter space.

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arXiv2018

Searching for Charged Higgs Bosons in the $B-L$ Supersymmetric Standard Model at the High Luminosity Large Hadron Collider

Upon assuming the $B-L$ Supersymmetric Standard Model (BLSSM) as theoretical framework accommodating a multi-Higgs sector, we assess the scope of the High Luminosity Large Hadron Collider (HL-LHC) in accessing charged Higgs bosons ($H^\pm$) produced in pairs from $Z'$ decays. We show that, by pursuing both di-jet and tau-neutrino decays, several signals can be established for $H^\pm$ masses ranging from about $M_{W}$ to above $m_t$ and $Z'$ masses between 2.5 TeV and 3.5 TeV. The discovery can be attained, even in a background free environment in some cases, owing to the fact that the very massive resonating $Z'$ ejects the charged Higgs bosons at very high transverse momentum, a kinematic region where any SM noise is hugely depleted.

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arXiv2018

Exploring Sensitivity to NMSSM Signatures with Low Missing Transverse Energy at the LHC

We examine scenarios in the Next-to-Minimal Supersymmetric Standard Model (NMSSM), where pair-produced squarks and gluinos decay via two cascades, each ending in a stable neutralino as Lightest Supersymmetric Particle (LSP) and a Standard Model (SM)-like Higgs boson, with mass spectra such that the missing transverse energy, $E_{T}^{\text{miss}}$, is very small. Performing two-dimensional parameter scans and focusing on the hadronic $H\rightarrow b\bar{b}$ decay giving a $b\bar{b}b\bar{b} + E_{T}^{\text{miss}}$ final state we explore the sensitivity of a current LHC general-purpose jets+$E_{T}^{\text{miss}}$ analysis to such scenarios.

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