arXiv subjects

Igor P. Volobuev

Publications and source records attributed to Igor P. Volobuev.

At least 19 recordsLinked to original sources

arXiv2021

Comparative analysis of the Compton ionization of Hydrogen and Positronium

The paper deals with the Compton disintegration of positronium and a comparison of the differential cross sections of this process with the similar cross sections in the case of the Compton ionization of the hydrogen atom. Special attention is paid to the resonances arising, when the electron and positron move parallel to each other in continuum states with the same velocities and zero relative momentum. It is likely that a manifestation of this effect in the double differential cross section is found as an additional peak, which grows with a decrease in the photon energy.

quant-ph↗

arXiv2020

Kinematically complete experimental study of Compton scattering at helium atoms near the ionization threshold

Compton scattering is one of the fundamental interaction processes of light with matter. Already upon its discovery [1] it was described as a billiard-type collision of a photon kicking a quasi-free electron. With decreasing photon energy, the maximum possible momentum transfer becomes so small that the corresponding energy falls below the binding energy of the electron. Then ionization by Compton scattering becomes an intriguing quantum phenomenon. Here we report a kinematically complete experiment on Compton scattering at helium atoms below that threshold. We determine the momentum correlations of the electron, the recoiling ion, and the scattered photon in a coincidence experiment finding that electrons are not only emitted in the direction of the momentum transfer, but that there is a second peak of ejection to the backward direction. This finding links Compton scattering to processes as ionization by ultrashort optical pulses [2], electron impact ionization [3,4], ion impact ionization [5,6], and neutron scattering [7] where similar momentum patterns occur.

physics.atom-ph↗

arXiv2019

Coherence length of neutrino oscillations in quantum field-theoretical approach

We consider a novel quantum field-theoretical approach to the description of processes passing at finite space-time intervals based on the Feynman diagram technique in the coordinate representation. The most known processes of this type are neutrino and neutral kaon oscillations. The experimental setting of these processes requires one to adjust the rules of passing to the momentum representation in the Feynman diagram technique in accordance with it, which leads to a modification of the Feynman propagator in the momentum representation. The approach does not make use of wave packets, both initial and final particle states are described by plane waves, which simplifies the calculations considerably. We consider neutrino oscillation processes, where the neutrinos are produced in three-particle weak decays of nuclei and detected in the charged-current interaction with nuclei or in the charged- and neutral-current interactions with electrons. Particular examples are considered and it is shown that the momentum spread of the produced neutrinos and the energy dependence of the differential cross section of the detection process result in the suppression of neutrino oscillation, which is characterized by a coherence length specific for a pair of production and detection processes. This coherence length turns out to be much less than the coherence length in the standard quantum-mechanical approach defined by the quantum uncertainty of neutrino momentum.

hep-ph↗

arXiv2018

Neutrino oscillation processes with a change of lepton flavor in quantum field-theoretical approach

The oscillating probabilities of lepton flavor changing neutrino oscillation processes, where neutrinos are detected by charged-current and neutral-current interactions, are calculated in a quantum field-theoretical approach to neutrino oscillations based on a modification of the Feynman propagator in the momentum reprsentation. The approach is most similar to the standard Feynman diagram technique in the momentum representation. It is found that the oscillating distance-dependent probabilities of detecting an electron in experiments with neutrino production in the muonic decay of $π^+$-meson and the detection of the produced neutrino by charged-current and neutral-current interactions exactly coincide with the corresponding probabilities calculated in the standard approach.

hep-ph↗

arXiv2018

Coherent Compton scattering from hydrogen and helium atoms

We develop an approach to describing coherent Compton scattering of photons in the keV energy range from hydrogen and helium atoms based on a relativistic version of the AA-approximation within the standard perturbative S-matrix formalism. The resulting formulas for the cross section take into account the effects of the electron boundness and correctly reproduce the behavior of the cross section at large photon energies, where it goes to Thomson formula, which coincides with the Klein-Nishina-Tamm formula for the cross section in the non-relativistic limit.

physics.atom-ph↗

arXiv2017

Neutrino oscillation processes in quantum field-theoretical approach

It is shown that neutrino oscillation processes can be consistently described in the framework of quantum field theory. Namely, the oscillating electron survival probabilities in experiments with neutrino detection by charged-current and neutral-current interactions are calculated in the quantum field-theoretical approach to neutrino oscillations based on a modification of the Feynman propagator. The approach is most similar to the standard Feynman diagram technique in the momentum representation. It is found that the oscillating distance-dependent probabilities of detecting an electron in experiments with neutrino detection by charged-current and neutral-current interactions exactly coincide with the corresponding probabilities calculated in the standard approach.

hep-ph↗

arXiv2017

Quantum field-theoretical description of neutrino and neutral kaon oscillations

It is shown that the neutrino and neutral kaon oscillation processes can be consistently described in quantum field theory using only the mass eigenstates of neutrinos and neutral kaons. The distance-dependent and time-dependent parts of the amplitudes of these processes are calculated and the results turn out to be in accord with those of the standard quantum mechanical description of these processes based on the notion of neutrino flavor states and neutral kaon states with definite strangeness. However, the physical picture of the phenomena changes radically: now there are no oscillations of flavor or definite strangeness states, but, instead of it, there is an interference of amplitudes due to different virtual mass eigenstates.

hep-ph↗

arXiv2016

Can the 750 GeV diphoton LHC excess be due to a radion-dominated state?

We discuss the possibility of interpreting the 125 GeV scalar boson and the 750 GeV diphoton excess recently reported by the ATLAS and CMS experiments as a Higgs-dominated and a radion-dominated states respectively in a stabilized brane-world model. It is shown that in the simplest variant of the model, where only the gravitational degrees of freedom propagate in the bulk, the production cross section of the radion-dominated state with mass 750 GeV turns out to be too small in the allowed region of the model parameter space for explaining the nature of the excess in this approach.

hep-ph↗

arXiv2016

Some problems with reproducing the Standard Model fields and interactions in five-dimensional warped brane world models

In the present paper we examine, from the purely theoretical point of view and in a model-independent way, the case, when matter, gauge and Higgs fields are allowed to propagate in the bulk of five-dimensional brane world models with compact extra dimension, and the Standard Model fields and their interactions are supposed to be reproduced by the corresponding zero Kaluza-Klein modes. An unexpected result is that in order to avoid possible pathological behavior in the fermion sector, it is necessary to impose constraints on the fermion field Lagrangian. In the case when the fermion zero modes are supposed to be localized at one of the branes, these constraints imply an additional relation between the vacuum profile of the Higgs field and the form of the background metric. Moreover, this relation between the vacuum profile of the Higgs field and the form of the background metric results in the exact reproduction of the gauge boson and fermion sectors of the Standard Model by the corresponding zero mode four-dimensional effective theory in all the physically relevant cases, allowed by the absence of pathologies. Meanwhile, deviations from these conditions can lead either back to pathological behavior in the fermion sector or to a variance between the resulting zero mode four-dimensional effective theory and the Standard Model, which, depending on the model at hand, may, in principle, result in constraints putting the theory out of the reach of the present day experiments.

hep-th↗

arXiv2015

Higgs-radion mixing in stabilized brane world models

We consider a quartic interaction of the Higgs and Goldberger-Wise fields, which connects the mechanism of the extra dimension size stabilization with spontaneous symmetry breaking on our brane and gives rise to a coupling of the Higgs field to the radion and its KK tower. We estimate a possible influence of this coupling on the Higgs-radion mixing and study restrictions on model parameters from the LHC data.

hep-ph↗

arXiv2009

Testing extra dimensions below the production threshold of Kaluza-Klein excitations

We consider a stabilized RS1 model in the energy range below the direct production of KK states. In this range we work out the effective Lagrangian due to exchange of heavy KK tensor graviton and scalar radion states and compute explicitly the corresponding effective coupling constants. As an example, the Drell-Yan lepton pair production at the Tevatron and the LHC is analyzed in two situations, when the first KK resonance is too heavy to be directly detected at the colliders, and when the first KK resonance is visible but other states are still too heavy. It is shown that in both cases the contribution from the KK invisible tower leads to a modification of final particles distributions. In particular, for the second case a nontrivial interference between the first KK mode and the rest KK tower takes place. Expected 95% CL limits for model parameters for the Tevatron and the LHC are given. In the Appendix useful formulas for the cross sections and distributions of various new $2\to2$ processes via heavy KK tower exchange are presented, the new formulas containing nonzero particle masses for final state fermions and bosons. The formulas and numerical results are obtained by means of the CompHEP code, in which all new effective interactions are implemented providing a tool for simulation of corresponding events and a more detailed analysis.

hep-ph↗

arXiv2008

On a stabilized warped brane world without Planck brane

We discuss a stabilized brane world model with two branes, admitting the solution to the hierarchy problem due to the warped extra dimension and possessing a remarkable feature: the strength of gravitational interaction is of the same order on both branes, contrary to the case of the Randall-Sundrum model with a hierarchical difference of gravitational strength on the branes. The solution also admits the existence of two branes with an equal strength of gravitational interaction, which is of interest for treating the matter on the "mirror" brane as dark matter.

hep-th↗

arXiv2008

Single-brane world with stabilized extra dimension

We present a model describing a single brane with tension embedded into a five-dimensional space-time with compact extra dimension, which can be easily stabilized. We examine the linearized gravity in the model and obtain an expression for the four-dimensional Planck mass on the brane in terms of the model parameters. It is also shown that the scalar sector of the effective four-dimensional theory contain a tachyonic mode, and we discuss the problem of stability of the model.

hep-th↗

arXiv2007

Ghosts in the self-accelerating universe

The self-accelerating universe realizes the accelerated expansion of the universe at late times by large-distance modification of general relativity without a cosmological constant. The Dvali-Gabadadze-Porrati (DGP) braneworld model provides an explicit example of the self-accelerating universe. Recently, the DGP model becomes very popular to study the observational consequences of the modified gravity models as an alternative to dark energy models in GR. However, it has been shown that the self-accelerating universe in the DGP model contains a ghost at the linearized level. The ghost carries negative energy densities and it leads to the instability of the spacetime. In this article, we review the origin of the ghost in the self-accelerating universe and explore the physical implication of the existence of the ghost.

hep-th↗

arXiv2007

Physical degrees of freedom in stabilized brane world models

We consider brane world models with interbrane separation stabilized by the Goldberger-Wise scalar field. For arbitrary background, or vacuum configurations of the gravitational and scalar fields in such models, we construct the second variation Lagrangian, study its gauge invariance, find the corresponding equations of motion and decouple them in a suitable gauge. We also derive an effective four-dimensional Lagrangian for such models, which describes the massless graviton, a tower of massive gravitons and a tower of massive scalars. It is shown that for a special choice of the background solution the masses of the graviton excitations may be of the order of a few TeV, the radion mass of the order of 100 GeV, the inverse size of the extra dimension being tens of GeV. In this case the coupling of the radion to matter on the negative tension brane is approximately the same as in the unstabilized model with the same values of the fundamental five-dimensional energy scale and the interbrane distance.

hep-th↗

arXiv2006

Effective Lagrangians for linearized gravity in Randall-Sundrum model

We construct the second variation Lagrangian for Randall-Sundrum model with two branes, study its gauge invariance, find the corresponding equations of motion and decouple them. We also derive an effective Lagrangian for this model in the unitary gauge, which describes a massless graviton, massive gravitons and a massless scalar radion. It is shown that the mass spectra of these fields and their couplings to the matter are different on different branes.

hep-th↗

arXiv2006

Effective Lagrangians for physical degrees of freedom in the Randall-Sundrum model

We derive the second variation Lagrangian of the Randall-Sundrum model with two branes, study its gauge invariance and diagonalize it in the unitary gauge. We also show that the effective four-dimensional theory looks different on different branes and calculate the observable mass spectra and the couplings of the physical degrees of freedom of 5-dimensional gravity to matter.

hep-th↗

arXiv2005

A non-standard matter distribution in the RS1 model and the coupling constant of the radion

In the zero mode approximation we solve exactly the equations of motion for linearized gravity in the Randall-Sundrum model with a non-standard distribution of matter in the neighbourhood of the negative tension brane. It is shown that the form of this distribution can strongly affect the coupling of the radion to matter. We believe that such a situation can arise in models with a realistic mechanisms of matter localization.

hep-th↗