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Oleg Lychkovskiy

Publications and source records attributed to Oleg Lychkovskiy.

51 records · Page 3Linked to original sources
arXiv2014

Perpetual motion of a mobile impurity in a one-dimensional quantum gas

Consider an impurity particle injected in a degenerate one-dimensional gas of noninteracting fermions (or, equivalently, Tonks-Girardeau bosons) with some initial momentum $p_0$. We examine the infinite-time value of the momentum of the impurity, $p_\infty$, as a function of $p_0$. A lower bound on $|p_\infty(p_0)|$ is derived under fairly general conditions. The derivation, based on the existence of the lower edge of the spectrum of the host gas, does not resort to any approximations. The existence of such bound implies the perpetual motion of an impurity in a one-dimensional gas of noninteracting fermions or Tonks-Girardeau bosons at zero temperature. The bound has an especially simple and useful form when the interaction between the impurity and host particles is everywhere repulsive.

cond-mat.quant-gas↗
arXiv2013

Spin dynamics in finite cyclic XY model

Evolution of the z-component of a single spin in the finite cyclic XY spin 1/2 chain is studied. Initially one selected spin is polarized while other spins are completely unpolarized and uncorrelated. Polarization of the selected spin as a function of time is proportional to the autocorrelation function at infinite temperature. Initialization of the selected spin gives rise to two wave packets moving in opposite directions and winding over the circle. We express the correlation function as a series in winding number and derive tractable approximations for each term. This allows to give qualitative explanation and quantitative description to various finite-size effects such as partial revivals and transition from regular to erratic behavior.

quant-ph↗
arXiv2011

On the merit of a Central Limit Theorem-based approximation in statistical physics

The applicability conditions of a recently reported Central Limit Theorem-based approximation method in statistical physics are investigated and rigorously determined. The failure of this method at low and intermediate temperature is proved as well as its inadequacy to disclose quantum criticalities at fixed temperatures. Its high temperature predictions are in addition shown to coincide with those stemming from straightforward appropriate expansions up to (k_B T)^(-2). Our results are clearly illustrated by comparing the exact and approximate temperature dependence of the free energy of some exemplary physical systems.

cond-mat.stat-mech↗
arXiv2011

mu->e Gamma decay versus mu->eee bound and lepton flavor violating processes in supernova

Even tiny lepton flavor violation (LFV) due to some New Physics is able to alter the conditions inside a collapsing supernova core and probably to facilitate the explosion. LFV emerges naturally in a See-Saw type II model of neutrino mass generation. Experimentally LFV is constrained by rare lepton decay searches. In particular, strong bounds are imposed on the mu->eee branching ratio and on the mu-e conversion probability in muonic gold. Currently the mu->e gamma decay is under investigation in the MEG experiment which aims at dramatic increase of sensitivity in the next three years. We search for a See-Saw type II LFV pattern which fits all the experimental constraints, provides Br(mu->e gamma) not less than Br(mu->eee) and ensures a rate of LFV processes in supernova high enough to modify the supernova physics. These requirements are sufficient to eliminate almost all freedom in the model. In particular, they lead to a prediction 0.5*10^(-12) < Br(mu->e gamma)< 6*10^(-12), which is testable by MEG in the nearest future. The considered scenario also constrains neutrino mass-mixing pattern and provides lower and upper bounds on tau-lepton LFV decays. We also briefly discuss a model with a single bilepton in which the mu->eee decay is absent at the tree level.

hep-ph↗
arXiv2011

Entanglement, decoherence and thermal relaxation in exactly solvable models

Exactly solvable models provide an opportunity to study different aspects of reduced quantum dynamics in detail. We consider the reduced dynamics of a single spin in finite XX and XY spin 1/2 chains. First we introduce a general expression describing the evolution of the reduced density matrix. This expression proves to be tractable when the combined closed system (i.e. open system plus environment) is integrable. Then we focus on comparing decoherence and thermalization timescales in the XX chain. We find that for a single spin these timescales are comparable, in contrast to what should be expected for a macroscopic body. This indicates that the process of quantum relaxation of a system with few accessible states can not be separated in two distinct stages - decoherence and thermalization. Finally, we turn to finite-size effects in the time evolution of a single spin in the XY chain. We observe three consecutive stages of the evolution: regular evolution, partial revivals, irregular (apparently chaotic) evolution. The duration of the regular stage is proportional to the number of spins in the chain. We observe a "quiet and cold period" in the end of the regular stage, which breaks up abruptly at some threshold time.

quant-ph↗
arXiv2010

Lepton flavor violating New Physics and supernova explosion

Electrons and electron neutrinos in the inner core of the core-collapse supernova are highly degenerate and therefore numerous during a few seconds of explosion. In contrast, leptons of other flavors are non-degenerate and therefore relatively scarce. This is due to lepton flavor conservation. If this conservation law is broken by some non-standard interactions, electron neutrinos are converted to muon and tau-neutrinos, and electrons -- to muons. This affects the supernova dynamics and the supernova neutrino signal in several ways. In particular, the total neutrino luminosity in the first second of the collapse is increased due to the larger free path of the non-electron neutrinos. This effect may have important consequences as the increase of the neutrino luminosity is known to facilitate the explosion. We consider an extension of the Standard Model by scalar bileptons which mediate lepton flavor violation. It is shown that in case of TeV-mass bileptons the electron fermi gas is equilibrated with non-electron species inside the inner supernova core at a time-scale of order of (1-100) ms. In particular, a scalar triplet which generates neutrino masses through the see-saw type II mechanism is considered. Non-observation of rare decays and data on neutrino mixing and neutrino masses restrict possible lepton flavor violation effects in this case. However a region in the parameter space of the model exists which fits all the experimental constraints and provides lepton flavor violation sufficient for observable effects in supernova.

hep-ph↗
arXiv2010

A necessary condition for the thermalization of a quantum system coupled to a quantum bath

A system put in contact with a large heat bath normally thermalizes. This means that the state of the system approaches an equilibrium state, the latter depending only on macroscopic characteristics of the bath (e.g. temperature), but not on the initial state of the system. The above statement is the cornerstone of the equilibrium statistical mechanics; its validity and its domain of applicability are central questions in the studies of the foundations of statistical mechanics. In the present paper we concentrate on one aspect of thermalization, namely, on the system initial state independence (ISI) of the equilibrium state. A necessary condition for the system ISI is derived in the quantum framework. We use the derived condition to prove the absence of the system ISI in a specific model. Namely, we consider a single spin coupled to a large bath, the interaction being of a specific form. Although the model under consideration is nontrivial enough to exhibit the decoherence and the approach to equilibrium, the derived necessary condition is not fulfilled and thus the equilibrium state depends on the initial state of the spin.

quant-ph↗
arXiv2010

TeV-scale bileptons, see-saw type II and lepton flavor violation in core-collapse supernova

Electrons and electron neutrinos in the inner core of the core-collapse supernova are highly degenerate and therefore numerous during a few seconds of explosion. In contrast, leptons of other flavors are non-degenerate and therefore relatively scarce. This is due to lepton flavor conservation. If this conservation law is broken by some non-standard interactions, electron neutrinos are converted to muon and tau-neutrinos, and electrons - to muons. This affects the supernova dynamics and the supernova neutrino signal. We consider lepton flavor violating interactions mediated by scalar bileptons, i.e. heavy scalars with lepton number 2. It is shown that in case of TeV-mass bileptons the electron fermi gas is equilibrated with non-electron species inside the inner supernova core at a time-scale of order of (1-100) ms. In particular, a scalar triplet which generates neutrino masses through the see-saw type II mechanism is considered. It is found that supernova core is sensitive to yet unprobed values of masses and couplings of the triplet.

hep-ph↗
arXiv2009

Spin flip of neutrinos with magnetic moment in core-collapse supernova

Neutrino with magnetic moment can experience a chirality flip while scattering off charged particles. This effect may lead to important consequences for the dynamics and the neutrino signal of the core-collapse supernova. It is known that if neutrino is a Dirac fermion, then nu_L->nu_R transition induced by the chirality flip leads to the emission of sterile right-handed neutrinos. The typical energies of these neutrinos are rather high, E ~ (100-200)MeV. Neutrino spin precession in the magnetic field either inside the collapsing star or in the interstellar space may lead to the backward transition, nu_R->nu_L. Both possibilities are known to be interesting. In the former case high-energy neutrinos can deliver additional energy to the supernova envelope, which can help the supernova to explode. In the latter case high-energy neutrinos may be detected simultaneously with the "normal" supernova neutrino signal, which would be a smoking gun for the Dirac neutrino magnetic moment. We report the results of the calculation of the supernova right-handed neutrino luminosity up to 250 ms after bounce. They allow to refine the estimates of the energy emitted in right-handed neutrinos. Also the sensitivity of water Cherenkov detectors to the Dirac neutrino magnetic moment is estimated. For mu_Dirac=10^{-13}mu_B Super-Kamiokande is expected to detect at least few high-energy events from a galactic supernova explosion. Also we briefly discuss the case of Majorana neutrino magnetic moment. It is pointed out that spin flips may quickly equilibrate electron neutrinos with non-electron antineutrinos if mu_Majorana~10^{-12}mu_B. This may lead to various consequences for supernova physics.

hep-ph↗
arXiv2009

Purity sieve for models with factorizable interactions

Evolution of purity in case of factorizable interaction between an open system and an environment is investigated. We derive a simple expression for purity decrease at the first instants of evolution (when purity is close to unity). We find that purity at very small times is maximal when an initial state of an open system coincides with one of the eigenstates of the interaction operator, no matter how weak the interaction is. On the other hand it is widely known that in general eigenstates of the interaction are not pointer states. Therefore the procedure of selecting pointer states by purity maximization (known as "purity sieve") should not rely on short-time purity behavior. We propose a modification of the purity sieve criterion which approximately takes into account purity evolution at longer times. As an example of its applicability we recover known results for pointer states of a particle undergoing quantum Brownian motion; we point out that the criterion is not applicable for some other models, however. It is argued that the proposed modified purity sieve may be used for selecting pointer states of a particle undergoing decoherence through collisions.

quant-ph↗
arXiv2008

Neutrino magnetic moment signatures in the supernova neutrino signal

It is known that if neutrino is a Dirac fermion with magnetic moment, then ν_L -> ν_R -> ν_L transition of supernova neutrinos may occur. The first stage of such transition is due to the neutrino spin flip inside the hot dense supernova core, while the second one - due to the neutrino spin precession in the galactic magnetic field on the way from the supernova to terrestrial detectors. This can result in the detection of 60-200 MeV neutrinos simultaneously with the "normal" supernova neutrino signal, which would be a smoking gun for the Dirac neutrino magnetic moment, μ. We argue that in case of a nearby supernova explosion (~10 kpc away from the Earth) one may observe such high-energy events in Super-Kamiokande if μ\gtrsim 10^{-13} μ_B, and in a Mt-scale detector if μ\gtrsim 0.5*10^{-13} μ_B. Such an observation by itself, however, may be not sufficient to determine the value of the magnetic moment, because of the ignorance of the interstellar magnetic field. We point out that if in addition a deficit of the neutronization burst neutrinos is established, it would be possible to extract the value of the magnetic moment from observations. We also briefly discuss a possible Majorana magnetic moment signature due to ν_e -> \barν_{μ,τ} flip inside the supernova core.

hep-ph↗
arXiv2007

Analysis of the SN1987A two-stage explosion hypothesis with account for the MSW neutrino flavour conversion

Detection of 5 events by the Liquid Scintillation Detector (LSD) on February, 23, 1987 was interpreted in the literature as the detection of neutrinos from the first stage of the two-stage supernova collapse. We pose rigid constraints on the properties of the first stage of the collapse, taking into account neutrino flavour conversion due to the MSW-effect and general properties of supernova neutrino emission. The constraints depend on the unknown neutrino mass hierarchy and mixing angle θ_{13}.

astro-ph↗
arXiv2006

Constraints on neutrino mixing angle theta_13 and Supernova neutrino fluxes from the LSD neutrino signal from SN1987A

Detection of 5 events by the Liquid Scintillation Detector (LSD) on February, 23, 1987 was recently interpreted as a detection of the electron neutrino flux from the first stage of the two-stage Supernova collapse. We show that, if neutrino mass hierarchy is normal, such interpretation excludes values of neutrino mixing angle θ_{13} larger than 3\cdot 10^{-2}, independently of the particular Supernova collapse model. Also constraints on the original fluxes of neutrinos and antineutrinos of different flavours are obtained.

hep-ph↗