arXiv subjects

Zoltán Trócsányi

Publications and source records attributed to Zoltán Trócsányi.

At least 19 recordsLinked to original sources

arXiv2025

CP asymmetry factor in decays at finite temperature

We present in the conventional equilibrium approach to leptogenesis the complete leading order prediction for the CP asymmetry factor in finite-temperature decays involving Majorana neutrinos. As thermal effects are generally not negligible, the knowledge of the high temperature behavior of the underlying particle physics model, in particular that of mass generation, is required for reliable estimates of matter-antimatter asymmetry through the mechanism of leptogenesis. We present all necessary information needed to obtain the full one-loop evaluation for the thermal CP asymmetry factors for the processes $N_i\to ϕ+ L$ and $ϕ\to N_i+L$ at temperatures where they are kinematically allowed. We present a numerical comparison with previous formulae given in the literature.

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arXiv2025

CP violation at finite temperature

We present a comprehensive study of the finite temperature CP-asymmetry factor needed in the semi-classical treatment of leptogenesis originating from Majorana fermion decays into a lepton and a scalar particle. The imaginary part of the relevant one-loop integrals are evaluated using both the real time and the imaginary time formalisms of thermal quantum field theory. In the former we consider the retarded-advanced approach as well as the original thermal cutting method developed by Kobes and Semenoff. Specific care is directed towards showing the consistency between the various approaches. We show that the final physical result of the calculation is linear in the statistical factors and is consistent with what is obtained in the Kadanoff-Baym approach. We also present analytic expressions for the full CP-asymmetry factor in the form of well-behaved triple-integrals, and provide numerical benchmark predictions in a specific particle physics model.

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arXiv2025

Precision Higgs Constraints in U(1) Extensions of the Standard Model with a Light Z'-Boson

Anomaly free $U(1)$ extensions of the standard model (SM) predict a new neutral gauge boson $Z'$. When the $Z'$ obtains its mass from the spontaneous breaking of the new $U(1)$ symmetry by a new complex scalar field, the model also predicts a second real scalar $s$ and the searches for the new scalar and the new gauge boson become intertwined. We present the computation of production cross sections and decay widths of such a scalar $s$ in models with a light $Z'$ boson, when the decay $h\to Z' Z'$ may have a sizeable branching ratio. We show how Higgs signal strength measurement in this channel can provide stricter exclusion bounds on the parameters of the model than those obtained from the total signal strength for Higgs boson production.

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arXiv2024

Analysis of $(n+1)$ and $n$-parton contributions for computing QCD jet cross sections in the local analytic subtraction scheme

We analyze and implement the Local Analytic Sector Subtraction (LASS) scheme for handling infrared singularities in next-to-next-to-leading order (NNLO) calculations in perturbative QCD. We examine the key aspects of the scheme including sector function construction, singular limit parametrization, subtraction counterterm derivation, and integration techniques. As a proof-of-concept, we numerically implement LASS for the process $e^+e^- \rightarrow 3$ jets. In this study we examine the limiting behavior of subtraction terms for real-virtual contribution and explicitly demonstrate the pole cancellation of the double-virtual contribution. Differential cross sections are computed for several event shape observables, showing the stability and efficiency of LASS scheme. This work lays the foundation for developing an automated tool for NNLO QCD calculations using this promising scheme.

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arXiv2024

Exclusion bounds for neutral gauge bosons

We study how the recent experimental results constrain the gauge sectors of U(1) extensions of the standard model using a novel representation of the parameter space. We determine the bounds on the mixing angle between the massive gauge bosons, or equivalently, the new gauge coupling as a function of the mass $M_{Z'}$ of the new neutral gauge boson $Z'$ in the approximate range $(10^{-2},10^4)\,$GeV/$c^2$. We consider the most stringent bounds obtained from direct searches for the $Z'$. We also exhibit the allowed parameter space by comparing the predicted and measured values of the $ρ$ parameter and those of the mass of the $W$ boson. Finally, we discuss the prospects of $Z'$ searches at future colliders.

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arXiv2023

Particles and antiparticles

We review the concept of chirality and charge for particles and antiparticles. We point out that the commonly accepted equivalence of particles and antiparticles - with difference only in the opposite signs of their charges, which follows from the CPT invariance - is valid only for free non-chiral particles. We show that with the weak interaction turned on the equivalence of particles and antiparticles is violated. We also discuss that within the Standard Model even free neutrinos are exceptions, they can be produced only in chiral states. We conclude that in spite of a long history of antiparticles, interesting theoretical and experimental challenges remain in their complete understanding.

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arXiv2023

Precise prediction for the mass of the $W$ boson in gauged U(1) extensions of the standard model

We present the one-loop radiative corrections to the muon decay in U(1)$_z$ extensions of the standard model. We compute the mass of the $W$ boson using those corrections and compare it to an approximation of the complete one-loop prediction implemented in automated computational tools. We point out that the truncation of the complete formulas become unreliable if the mass of the $Z'$ boson, corresponding to the new U(1)$_z$ gauge group is larger than about 1 TeV.

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arXiv2023

Constraining flavour-universal nonstandard interactions and superweak extension of the standard model

Nonstandard neutrino interactions (NSI) arising from light and heavy mediators probe different sectors of the parameter space of models focusing on phenomena that require the extension of the standard model. High-energy scattering experiments are not relevant on constraining the NSI hiding a light mediator at the fundamental level, while flavour-universal NSI cannot be probed with neutrino oscillation experiments. Currently the only way to measure flavour-universal NSI with a light mediator is to rely on coherent elastic neutrino-nucleon scattering experiments, which we use to derive bounds for light mediator flavour-universal NSI. For light NSI, we obtain $\varepsilon^u \in [-14.85,14.79]$ and $\varepsilon^d \in [-13.19,13.84]$ (90~\% CL.). We also derive constraints on flavour-universal heavy NSI and find a 2$σ$ tension. Finally, we discuss the implications of the experiments on the allowed parameter space of a specific example model, called superweak extension of the standard model.

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arXiv2022

Vacuum stability and scalar masses in the superweak extension of the standard model

We study the allowed parameter space of the scalar sector in the superweak extension of the standard model (SM). The allowed region is defined by the conditions of (i) stability of the vacuum and (ii) perturbativity up to the Planck scale, (iii) the pole mass of the Higgs boson falls into its experimentally measured range. We employ renormalization group equations and quantum corrections at two-loop accuracy. We study the dependence on the Yukawa couplings of the sterile neutrinos at selected values. We also check the exclusion limit set by the precise measurement of the mass of the W boson. Our method for constraining the parameter space using two-loop predictions can also be applied to simpler models such as the singlet scalar extension of the SM in a straightforward way.

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arXiv2022

Sterile neutrino dark matter in a U(1) extension of the standard model

We explore the parameter space of a U(1) extension of the standard model -- also called the super-weak model -- from the point of view of explaining the observed dark matter energy density in the Universe. The new particle spectrum contains a complex scalar singlet and three right-handed neutrinos, among which the lightest one is the dark matter candidate. We explore both freeze-in and freeze-out mechanisms of dark matter production. In both cases, we find regions in the plane of the super-weak coupling vs. the mass of the new gauge boson that are not excluded by current experimental constraints. These regions are distinct and the one for freeze-out will be explored in searches for neutral gauge boson in the near future.

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arXiv2021

Super-weakly coupled U(1)$_z$ and GeV neutrinos

The $super$-$weak$ force combines three simple extensions of the Standard Model, one in gauge sector, one in fermion sector and one in scalar sector. Each of these extensions are well motivated by their rich phenomenology. Combined to a single framework, they can explain several open questions in particle physics and cosmology: the origin of dark matter, cosmic inflation, matter-antimatter asymmetry, neutrino masses and vacuum stability. We discuss the effects of the model on neutrino masses and phenomenology in the case where the heaviest sterile neutrinos have a GeV scale mass.

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arXiv2021

Experimental constraints on the neutrino and gauge parameters of the super-weak U(1) extension of the standard model

The super-weak force is a minimal, anomaly-free U(1) extension of the standard model (SM), designed to explain the origin of (i) neutrino masses and mixing matrix elements, (ii) dark matter, (iii) cosmic inflation, (iv) stabilization of the electroweak vacuum and (v) leptogenesis. We discuss the neutrino sector of this model in detail and study the allowed parameter space of the neutrino Yukawa matrices and mixing matrix elements. The model generates nonstandard neutrino interactions, whose allowed experimental limits are used to constrain the parameter space of the model. We provide benchmark points in the relevant parameter space that fall within the sensitivity region of the SHiP and MATHUSLA experiments.

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arXiv2021

One-loop corrections to light neutrino masses in gauged U(1) extensions of the standard model

We consider gauged U(1) extensions of the standard model of particle physics with three right-handed sterile neutrinos and a singlet scalar. The neutrinos obtain mass via the type I seesaw mechanism. We compute the one loop corrections to the elements of the tree level mass matrix of the light neutrinos and show explicitly the cancellation of the gauge dependent terms. We present a general formula for the gauge independent, finite one-loop corrections for arbitrary number new U(1) groups, new complex scalars and sterile neutrinos. We estimate the size of the corrections relative to the tree level mass matrix in a particular extension, the super-weak model.

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arXiv2020

Groomed jet mass at high precision

We present predictions of the distribution of groomed heavy jet mass in electron-positron collisions at the next-to-next-to-leading order accuracy matched with the resummation of large logarithms to next-to-next-to-next-to-leading logarithmic accuracy. Resummation at this accuracy is possible through extraction of necessary two-loop constants and three-loop anomalous dimensions from fixed-order codes.

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arXiv2020

Two- and Three-Loop Data for Groomed Jet Mass

We discuss the status of resummation of large logarithmic contributions to groomed event shapes of hadronic final states in electron-positron annihilation. We identify the missing ingredients needed for next-to-next-to-next-to-leading logarithmic (NNNLL) resummation of the mMDT groomed jet mass in $e^+e^-$ collisions: the low-scale collinear-soft constants at two-loop accuracy, $c_{S_c}^{(2)}$, and the three-loop non-cusp anomalous dimension of the global soft function, $γ_S^{(2)}$. We present a method for extracting those constants using fixed-order codes: the EVENT2 program to obtain the color coefficients of $c_{S_c}^{(2)}$, and MCCSM for extracting $γ_S^{(2)}$. We present all necessary formulae for resummation of the mMDT groomed heavy jet mass distribution at NNNLL accuracy.

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arXiv2019

Particle physics model of curvaton inflation in a stable universe

We investigate a particle physics model for cosmic inflation based on the following assumptions: (i) there are at least two complex scalar fields; (ii) the scalar potential is bounded from below and remains perturbative up to the Planck scale; (iii) we assume slow-roll inflation with maximally correlated adiabatic and entropy fluctuations 50--60 e-folds before the end of inflation. The energy scale of the inflation is set automatically by the model. Assuming also at least one massive right handed neutrino, we explore the allowed parameter space of the scalar potential as a function of the Yukawa coupling of this neutrino.

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arXiv2019

High precision determination of $α_s$ from a global fit of jet rates

We present state-of-the-art extractions of the strong coupling based on N$^3$LO+NNLL accurate predictions for the two-jet rate in the Durham clustering algorithm at $e^+e^-$ collisions, as well as a simultaneous fit of the two- and three-jet rates taking into account correlations between the two observables. The fits are performed on a large range of data sets collected at LEP and PETRA colliders, with energies spanning from $35$ GeV to $207$ GeV. Owing to the high accuracy of the predictions used, the perturbative uncertainty is considerably smaller than that due to hadronization. Our best determination at the $Z$ mass is $α_s(M_Z) = 0.11881 \pm 0.00063(exp.) \pm 0.00101(hadr.) \pm 0.00045(ren.) \pm 0.00034(res.)$, which is in agreement with the latest world average and has a comparable total uncertainty.

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arXiv2019

Stability of the vacuum as constraint on $U$(1) extensions of the standard model

In the standard model the running quartic coupling becomes negative during its renormalization group flow, which destabilizes the vacuum. We consider U(1) extensions of the standard model, with an extra complex scalar field and a Majorana-type neutrino Yukawa coupling. These additional couplings affect the renormalization group flow of the quartic couplings. We compute the beta-functions of the extended model at one-loop order in perturbation theory and study how the parameter space of the new scalar couplings can be constrained by the requirement of stable vacuum and perturbativity up to the Planck scale.

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