arXiv subjects

Orlando Panella

Publications and source records attributed to Orlando Panella.

At least 19 recordsLinked to original sources

arXiv2025

Radiative corrections to the $\rm S, T, U$ parameters and their impact on the $W$ boson mass in the 331 model

We investigate radiative corrections to electroweak precision observables, specifically the Peskin--Takeuchi parameters $\mathrm{S}$, $\mathrm{T}$, and $\mathrm{U}$, in the $SU(3)_C \times SU(3)_L \times U(1)_X$ (331) model with $\beta = -\sqrt{3}$. Using the SARAH and SPheno packages, we compute the mass spectrum and low-energy observables. We show that these parameters place strong constraints on the model, requiring most of the scalar masses to lie in the TeV range or below, and imposing indirect bounds on the newly predicted gauge bosons. Furthermore, we demonstrate that the model can accommodate the $W$ boson mass anomaly reported by the CDF collaboration, should future measurements confirm its persistence.

hep-ph↗

arXiv2025

Connecting $t$-channel Dark Matter Models to the Standard Model Effective Field Theory

We investigate the connection between simplified dark matter models featuring a $t$-channel scalar mediator and the Standard Model Effective Field Theory (SMEFT). We focus on scenarios with fermionic dark matter interacting with leptons, under the assumption of Minimal Flavor Violation. The dimension-six SMEFT Wilson coefficients are computed in the Warsaw basis at one loop, with the aid of Matchete. Assuming a compressed mass spectrum for the dark matter and the mediator, we incorporate coannihilations, Sommerfeld enhancement, and bound-state effects in the relic density calculation. We then analyze the interplay between the dark matter energy density, global SMEFT fits, and direct detection constraints. Our results show that SMEFT bounds, though loop-suppressed, can meaningfully constrain the parameter space for $m_\chi \gtrsim 0.5$ TeV and $\mathcal{O}(1)$ portal couplings.

hep-ph↗

arXiv2025

Very high energy cosmic ray particles from the Kerr black hole at the galaxy center

Conventional general relativity supplies the notion of a vacuum tension and thus a maximum force $F_{max}=c^4/4G\approx\ 3\times 10^{43}$ Newtons, that is realized for a black hole. In conjunction with the Wilson area rule, we are thus led to the surface confinement of the mass of a black hole analogous to the surface confinement of quarks. The central result of our paper is that PeV scale protons exist on the surface of a Kerr black hole residing at our galactic center that is in concert with the HAWC Collaboration result of a PeVatron at the galactic center.

astro-ph.HE↗

arXiv2024

Searching for type I seesaw mechanism in a two Heavy Neutral Leptons scenario at FCC-ee

This paper investigates the search for heavy neutral leptons (HNL) in the type I seesaw mechanism at the Future Circular Collider in its $e^+e^-$ stage (FCC-ee), considering a luminosity of 125 ab$^{-1}$ collected at $\sqrt{s}=$91.2 GeV. The study examines two generations of heavy neutral leptons produced in association with Standard Model (SM) neutrinos and decaying to a purely leptonic final state. This theoretical framework can explain neutrino oscillations and other open questions of the SM, providing a broader perspective on the relevance of this experimental search. The analysis is performed using a fast simulation of the IDEA detector concept to study potential HNL interactions at the FCC-ee. The sensitivity contours are obtained from a selection of kinematic variables aimed at improving the signal-to-background ratio for the prompt production case. In the case of long-lived HNLs, the background can be almost fully eliminated by exploiting their displaced decay vertices. The study shows that the FCC-ee has a significant sensitivity to observing these objects in a region of the phase space not accessible by other experiments.

hep-ph↗

arXiv2024

Searching for exclusive leptoquarks with the Nambu-Jona-Lasinio composite model at the LHC and HL-LHC

We present a detailed study concerning a new physics scenario involving four fermion operators of the Nambu-Jona-Lasinio type characterized by a strong-coupling ultraviolet fixed point where composite particles are formed as bound states of elementary fermions at the scale $Λ={\cal O}(\text{TeV})$. After implementing the model in the Universal FeynRules Output format, we focus on the phenomenology of the scalar leptoquarks at the LHC and the High-Luminosity option. Leptoquark particles have undergone extensive scrutiny in the literature and experimental searches, primarily relying on pair production and, more recently, incorporating single, t-channel, and lepton-induced processes. This study marks, for the first time, the examination of these production modes at varying jet multiplicities. Novel mechanisms emerge, enhancing the total production cross-section, especially for leptoquarks couplings to higher fermion generations. A global strategy is devised to capture all final state particles produced in association with leptoquarks or originating from their decay, which we termed ``exclusive'', in an analogy to the nomenclature used in nuclear reactions. The assessment of the significance in current and future LHC runs, focusing on the case of leptoquark coupling to a muon - $\textit{c}$ quark pair, reveals superior sensitivity compared to ongoing searches. Given this heightened discovery potential, we advocate the incorporation of exclusive leptoquark searches in future investigations at the LHC.

hep-ph↗

arXiv2024

The Muon Anomalous Magnetic Moment in the Excited Fermion Paradigm

Extensions of the Standard Model featuring excited fermions present an interesting framework that motivates the search for exotic particles at the LHC. Additionally, these extensions offer potential explanations for the muon's anomalous magnetic moment and other precision observables, shedding light on the energy scale and key parameters of the new theory. Our analysis focuses on the one-loop radiative correction originating from excited lepton doublet and triplet states using the effective Lagrangian approach. The bounds derived from the $(g-2)_\mu$ anomaly can be complemented with the ones arising from other observables like the electroweak precision observable $\Delta \rho$ and the signals from direct LHC searches to constraint the effective theory. Our results suggest that the $(g-2)_\mu$ anomaly can be addressed within a very narrow region of the effective theory scale. Consequently, this imposes indirect constraints on the parameter space of excited fermions.

hep-ph↗

arXiv2023

Constraints on NJL four-fermion effective interactions from neutrinoless double beta decay

We study the contribution of a heavy right-handed Majorana neutrino to neutrinoless double beta decay ($0νββ$) via four-fermion effective interactions of Nambu-Jona-Lasinio (NJL) type. In this physical scenario, the sterile neutrino contributes to the nuclear transition through gauge, contact, and mixed interactions. Using the lower limit on the half-life of $0νββ$ from the KamLAND-Zen experiment, we then constrain the effective right-handed coupling between the sterile neutrino and the $W$ boson: $\mathcal{G}^{W}_{R}$. Eventually, we show that the obtained bounds are compatible with those found in the literature, which highlights the complementarity of this type of phenomenological study with high-energy experiments.

hep-ph↗

arXiv2023

Quantum backflow of a Dirac fermion on a ring

We study the quantum backflow problem of a relativistic charged Dirac fermion constrained to move on a ring of radius $R$. Using the relativistic current operator we compute the probability flux through a generic time interval to show emergence of quantum backflow. We also discuss the limiting case when the particle moves along a line.

quant-ph↗

arXiv2020

Reinterpretation of LHC Results for New Physics: Status and Recommendations after Run 2

We report on the status of efforts to improve the reinterpretation of searches and measurements at the LHC in terms of models for new physics, in the context of the LHC Reinterpretation Forum. We detail current experimental offerings in direct searches for new particles, measurements, technical implementations and Open Data, and provide a set of recommendations for further improving the presentation of LHC results in order to better enable reinterpretation in the future. We also provide a brief description of existing software reinterpretation frameworks and recent global analyses of new physics that make use of the current data.

hep-ph↗

arXiv2020

Phenomenology at the LHC of composite particles from strongly interacting Standard Model fermions via four-fermion operators of NJL type

A new physics scenario shows that four-fermion operators of Nambu-Jona-Lasinio (NJL) type have a strong-coupling UV fixed point, where composite fermions $F$ (bosons $Π$) form as bound states of three (two) SM elementary fermions and they couple to their constituents via effective contact interactions at the composite scale $Λ\approx {\cal O} $(TeV). We present a phenomenological study to investigate such composite particles at the LHC by computing the production cross sections and decay widths of composite fermions in the context of the relevant experiments at the LHC with $pp$ collisions at $\sqrt{s}={\rm 13}$ TeV and $\sqrt{s}={\rm 14}$ TeV. Systematically examining all the different composite particles $F$ and the signatures with which they can manifest, we found a vast spectrum of composite particles $F$ that has not yet been explored at the LHC. Recasting the recent CMS results of the resonant channel $pp\rightarrow e^+F \rightarrow e^+e^- q\bar{q}'$, we find that the composite fermion mass $m_F$ below 4.25 TeV is excluded for $Λ$/$m_F$ = 1. We further highlight the region of parameter space where this specific composite particle $F$ can appear using 3 ab$^{-1}$, expected by the High-Luminosity LHC, computing 3 and 5 $σ$ contour plots of its statistical significance.

hep-ph↗

arXiv2019

Quantization of nonlocal fractional field theories via the extension problem

We use the extension problem proposed by Caffarelli and Silvestre to study the quantization of a scalar nonlocal quantum field theory built out of the fractional Laplacian. We show that the quantum behavior of such a nonlocal field theory in $d$-dimensions can be described in terms of a local action in $d+1$ dimensions which can be quantized using the canonical operator formalism though giving up local commutativity. In particular, we discuss how to obtain the two-point correlation functions and the vacuum energy density of the nonlocal fractional theory as a brane limit of the bulk correlators. We show explicitly how the quantized extension problem reproduces exactly the same particle content of other approaches based on the spectral representation of the fractional propagator. We also briefly discuss the inverse fractional Laplacian and possible applications of this approach in general relativity and cosmology.

hep-th↗

arXiv2018

Like-sign dileptons with mirror type composite neutrinos at the HL-LHC

Within a mirror type assignment for the excited composite fermions the neutrino mass term is built up from a Dirac mass, $m_*$, which gives the mass of charged lepton component of the $SU(2)$, right-handed, doublet, and a Majorana mass, $m_L$, for the left-handed component (singlet) of the excited neutrino. The mass matrix is diagonalized leading to two Majorana mass eigenstates. The active neutrino field $ν^*_R$ is thus a superposition of the two mass eigenstates with mixing coefficients which depend on the ratio $m_L/m_*$. We discuss the prospects of discovery of these physical states at the HL-LHC as compared with the previous searches of composite Majorana neutrinos at the LHC based on sequential type Majorana neutrinos.

hep-ph↗

arXiv2017

Leptogenesis and composite heavy neutrinos with gauge mediated interactions

Leptogenesis is an appealing framework to account for the baryon asymmetry in the universe. To this end physics beyond the Standard Model is demanded. In this paper we investigate the possibility to attain successful leptogenesis with composite Majorana neutrinos. We work in the framework of effective gauge mediated and contact interactions without any reference to an underlying compositeness theory. This approach is the one adopted in all current experimental searches for composite fermions at colliders. In the case of gauge mediated interactions, we calculate the CP asymmetry in heavy composite neutrino decays. Both the direct and indirect CP asymmetry are derived and resonant leptogenesis is also discussed. We find that the Sakharov conditions can be met and, for some choice of the parameters, the correct order of magnitude of the baryon asymmetry is reproduced.

hep-ph↗

arXiv2017

Thermodynamics of Quantum Phase Transitions of a Dirac oscillator in a homogenous magnetic field

The Dirac oscillator in a homogenous magnetic field exhibits a chirality phase transition at a particular (critical) value of the magnetic field. Recently, this system has also been shown to be exactly solvable in the context of noncommutative quantum mechanics featuring the interesting phenomenon of re-entrant phase transitions. In this work we provide a detailed study of the thermodynamics of such quantum phase transitions (both in the standard and in the noncommutative case) within the Maxwell-Boltzmann statistics pointing out that the magnetization has discontinuities at critical values of the magnetic field even at finite temperatures.

cond-mat.stat-mech↗

arXiv2017

Unparticle Casimir effect

In this paper we present the un-Casimir effect, namely the study of the Casimir energy in the presence of an unparticle component in addition to the electromagnetic field contribution. The distinctive feature of the un-Casimir effect is a fractalization of metallic plates. This result emerges through a new dependence of the Casimir energy on the plate separation that scales with a continuous power controlled by the unparticle dimension. As long as the perfect conductor approximation is valid, we find bounds on the unparticle scale that are independent of the effective coupling constant between the scale invariant sector and ordinary matter. We find regions of the parameter space such that for plate distances around $5μ$m and larger the un-Casimir bound wins over the other bounds.

hep-ph↗

arXiv2014

Pseudo Hermitian interactions in the Dirac Equation

We consider $(2+1)$ dimensional massless Dirac equation in the presence of complex vector potentials. It is shown that such vector potentials (leading to complex magnetic fields) can produce bound states and the Dirac Hamiltonians are $η$-pseudo Hermitian. Some examples have been explicitly worked out.

hep-th↗

arXiv2014

Searching Doubly Charged Leptons at Present and Future Colliders

The production at the LHC of exotic excited leptons of charge $Q = +2e$ is considered. Such states are predicted in composite models with extended isospin multiplets ($I_{W}=1$ and $I_{W}=3/2$). The coupling among these doubly charged leptons and Standard Model fermions may occurs either via gauge or contact interactions. In the former case the decay channels are more constrained. We study the production cross section at the LHC of $L^{++}$ ($pp \rightarrow L^{++} \, \ell^{-}$) and focus on the leptonic signature deriving from the subsequent decays $L^{++} \rightarrow W^{+} \ell^{+} \rightarrow \ell^{+} \ \ell^{+} \, ν_l $. The invariant mass distribution of the like-sign dilepton exhibits a sharp end-point corresponding to excited doubly charged lepton mass $m^{*}$. A preliminary study for the production of doubly charged leptons at the future linear colliders, by considering the process $e^{-} e^{-} \rightarrow L_{e}^{--} \, ν_{e}$, is carried out. Both the contact and gauge interaction mechanisms are investigated and compared.

hep-ph↗

arXiv2010

Threshold production of meta-stable bound states of Kaluza Klein excitations in Universal Extra Dimensions

We study the formation and detection at the next linear e^+e^- collider of bound states of level-1 quark Kaluza-Klein excitations B_KK within a scenario of universal extra-dimensions (UED). The interactions of such Kaluza-Klein excitations are modeled by an alpha_s driven Coulomb potential. In order to obtain the threshold cross-section, we employ the Green function method which is known to properly describe the peaks below threshold and to yield a net increase in the continuum region (above threshold) relative to the naive Born cross-section. We study such effect at different values of the scale (R^-1) of the extra-dimensions with an explicit calculation of the mass spectrum as given by radiative corrections. The overall effect is roughly 2.7 at R^-1=300 GeV and goes down to 2.2 at R^-1=1000 GeV and a relatively large number of events is expected from N_events ~ 2.5*10^4 at R^-1=300 GeV down to N_events ~ 10^3 at R^-1=1000 GeV at the anticipated annual integrated luminosity of L_0= 100 fb^-1. We finally discuss some potentially observable signatures such as the multilepton channels 2j + 2l + missing energy, and 2j + 4l + missing energy for which we estimate statistical significance >~ 2 for R^-1 up to 600 ~ 700 GeV.

hep-ph↗