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S. I. Godunov

Publications and source records attributed to S. I. Godunov.

At least 19 recordsLinked to original sources
arXiv2026

Importance of unitarity in the search for heavy neutrinos in $e^+ e^- \to W^+ W^-$

We study the process $e^+e^- \to W^+W^-$ with the aim of estimating the prospects for observing heavy neutrinos contributions at future $e^+e^-$-colliders. In this work, we consider two implementations of heavy-light neutrino mixing: a linearized mixing approximation applied in popular models and an exact unitary mixing scheme. We conclude that the approximate realization leads to physically incorrect results for this process, while exact unitary mixing provides some signatures that can be experimentally checked.

hep-ph↗
arXiv2025

Correction to $CP$-asymmetry in $Υ(4S)$ decays due to the admixture of $B^0 \bar B^0$ in a $C$-even state

$BB$ pairs from $Υ(4S)\to BB$ decays are in $C$-odd state. However, there is a small admixture of the $C$-even state and it modifies the time dependent $CP$-asymmetry. The $C$-even component appears due to soft photon emission, breaking the pure $C$-odd nature of the initial state. Using the two-particle wave function formalism, we derive analytical expressions for $CP$-asymmetry in both pure and mixed $C$-parity states. We emphasize the strong energy dependence of the admixture magnitude.

hep-ph↗
arXiv2024

libepa -- a C++/Python library for calculations of cross sections of ultraperipheral collisions

The library provides a set of C++/Python functions for computing cross sections of ultraperipheral collisions of high energy particles under the equivalent photons approximation. Cross sections are represented through multiple integrals over the phase space. The integrals are calculated through recurrent application of algorithms for one dimensional integration. The paper contains an introduction to the theory of ultraperipheral collisions, discusses the library approach and provides a few examples of calculations.

hep-ph↗
arXiv2021

Production of heavy charged particles in proton-proton ultraperipheral collisions at the Large Hadron Collider: survival factor

Ultraperipheral collisions of high energy protons are a source of approximately real photons colliding with each other. Photon fusion can result in production of yet unknown charged particles in very clean events. The cleanliness of such an event is due to the requirement that the protons survive during the collision. Finite sizes of the protons reduce the probability of such outcome compared to point-like particles. We calculate the survival factors and cross sections for the production of heavy charged particles at the Large Hadron Collider.

hep-ph↗
arXiv2021

LHC as a photon-photon collider: bounds on $Γ_{X\toγγ}$

In the relatively recent CMS data, there is a hint on the existence of a resonance with the mass 28 GeV coupling to muons. Such a resonance should also couple to photons through the fermion loop, therefore it can be searched for in ultraperipheral collisions (UPC) of protons. We set an upper bound on the $X γγ$ coupling constant from the data on $μ^+ μ^-$ pair production in UPC at the LHC. Our approach can be used for similar resonances should they appear in the future.

hep-ph↗
arXiv2020

Quasistable charginos in ultraperipheral proton-proton collisions at the LHC

We propose a model-independent approach for the search of charged long-lived particles produced in ultraperipheral collisions at the LHC. The main idea is to improve event reconstruction at ATLAS and CMS with the help of their forward detectors. Detection of both scattered protons in forward detectors allows complete recovery of event kinematics. Though this requirement reduces the number of events, it greatly suppresses the background, including the large background from the pile-up.

hep-ph↗
arXiv2018

Evolution of thick domain walls in inflationary and $p=wρ$ universe

We study the evolution of thick domain walls in the different models of cosmological inflation, in the matter-dominated and radiation-dominated universe, or more generally in the universe with the equation of state $p=wρ$. We have found that the domain wall evolution crucially depends on the time-dependent parameter $C(t)=1/(H(t)δ_0)^2$, where $H(t)$ is the Hubble parameter and $δ_0$ is the thickness of the wall in flat space-time. For $C(t)>2$ the physical thickness of the wall, $a(t)δ(t)$, tends with time to $δ_0$, which is microscopically small. Otherwise, when $C(t) \leq 2$, the wall steadily expands and can grow up to a cosmologically large size.

gr-qc↗
arXiv2018

Dimuon resonance near 28 GeV and muon anomaly

We discuss if the resonance recently observed by CMS can be responsible for the deviation of the experimentally measured muon anomalous magnetic moment from the theoretical prediction.

hep-ph↗
arXiv2018

Resonances in positron scattering on a supercritical nucleus and spontaneous production of $e^{+}e^{-}$ pairs

We re-examine the physics of supercritical nuclei, specially focusing on the scattering phase $δ_{\varkappa}$ and its dependence on the energy $\varepsilon$ of the diving electronic level, for which we give both exact and approximate formulas. The Coulomb potential $Zα/r$ is rounded to the constant $Zα/R$ for $r < R$. We confirm the resonant behavior of $δ_{\varkappa}$ that we investigate in details. In addition to solving the Dirac equation for an electron, we solve it for a positron, in the field of the same nucleus. This clarifies the interpretation of the resonances. Our results are compared with claims made in previous works.

hep-ph↗
arXiv2016

Spatial structure of the modified Coulomb potential in a superstrong magnetic field

The modification of the Coulomb potential due to the enhancement of loop corrections in a superstrong magnetic field is studied numerically. We calculate the modified potential with high precision and obtain the pattern of equipotential lines. The results confirm the general features known from previous studies, however we emphasize some differences in potential structure that can be important for problems with spatially distributed charges.

hep-ph↗
arXiv2016

Evolution of thick domain walls in de Sitter universe

We consider thick domain walls in a de Sitter universe following paper by Basu and Vilenkin. However, we are interested not only in stationary solutions found therein, but also investigate the general case of domain wall evolution with time. When the wall thickness parameter, $δ_0$, is smaller than $H^{-1}/\sqrt{2}$, where $H$ is the Hubble parameter in de Sitter space-time, then the stationary solutions exist, and initial field configurations tend with time to the stationary ones. However, there are no stationary solutions for $δ_0 \geq H^{-1}/\sqrt{2}$. We have calculated numerically the rate of the wall expansion in this case and have found that the width of the wall grows exponentially fast for $δ_0 \gg H^{-1}$. An explanation for the critical value $δ_{0c} = H^{-1}/\sqrt{2}$ is also proposed.

gr-qc↗
arXiv2016

New Physics at 1 TeV?

If decays of a heavy particle S are responsible for the diphoton excess with invariant mass 750 GeV observed at the 13 TeV LHC run, it can be easily accomodated in the Standard Model. Two scenarios are considered: production in gluon fusion through a loop of heavy isosinglet quark(s) and production in photon fusion through a loop of heavy isosinglet leptons. In the second case many heavy leptons are needed or/and they should have large electric charges in order to reproduce experimental data on $σ(pp \to SX) \cdot \mathrm{Br}(S \to γγ)$.

hep-ph↗
arXiv2015

Separated matter and antimatter domains with vanishing domain walls

We present a model of spontaneous (or dynamical) C and CP violation where it is possible to generate domains of matter and antimatter separated by cosmologically large distances. Such C(CP) violation existed only in the early universe and later it disappeared with the only trace of generated baryonic and/or antibaryonic domains. So the problem of domain walls in this model does not exist. These features are achieved through a postulated form of interaction between inflaton and a new scalar field, realizing short time C(CP) violation.

astro-ph.CO↗
arXiv2015

Suppression of $H\to VV$ decay channels in the Georgi-Machacek model

The $H\to ZZ$ decay mode is usually considered as one of the most promising ways to discover new heavy neutral scalar $H$. We show that in the Georgi-Machacek model it is possible to get large enhancement of double SM-like Higgs boson production due to $H$ decays while $ZZ$ and $WW$ decay channels could be highly suppressed.

hep-ph↗