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O. K. Vorov

Publications and source records attributed to O. K. Vorov.

At least 19 recordsLinked to original sources
arXiv2002

Rotating ground states of trapped Bose atoms with arbitrary two-body interactions

In a k-dimensional system of weakly interacting Bose atoms trapped by a spherically symmetric and harmonic external potential, an exact expression is obtained for the rotating ground states at a fixed angular momentum. The result is valid for arbitrary interactions obeying minimal physical requirements. Depending on the sign of a modified scattering length, it reduces to either a collective rotation or a condensed vortex state, with no alternative. The ground state can undergo a kind of quantum phase transition when the shape of the interaction potential is smoothly varied.

cond-mat.stat-mech↗
arXiv2002

On "Do the attractive bosons condense?" by N. K. Wilkin, J. M. F. Gunn, R. A. Smith

Using Perron-Frobenius theorem, we prove that the results by Wilkin, Gunn and Smith [1] for the ground states of N Bose atoms rotating at the angular momentum L in a harmonic atomic trap with frequency omega interacting via attractive delta^2(r) forces, are valid for a broad class of predominantly attractive interactions V(r), not necessarily attractive for any r. The sufficient condition for the interaction is that all the two-body matrix elements allowed by the conservation of angular momentum k+l = m+n, are negative. This class includes, in particular, the Gaussian attraction of arbitrary radius, -1/r - Coulomb and log(r)-Coulomb forces, as well as all the short-range R << omega^{-1/2} interactions satisfying inequality int d^2r V(r) < 0. There is no condensation at L>> 1, and the angular momentum is concentrated in the collective ``center-of-mass'' mode.

cond-mat.stat-mech↗
arXiv2002

Condensed vortex ground states of rotating Bose-Einstein condensate in harmonic atomic trap

We study a system of $N$ Bose atoms trapped by a symmetric harmonic potential, interacting via weak central forces. Considering the ground state of the rotating system as a function of the two conserved quantities, the total angular momentum and its collective component, we develop an algebraic approach to derive exact wave functions and energies of these ground states. We describe a broad class of the interactions for which these results are valid. This universality class is defined by simple integral condition on the potential. Most of the potentials of practical interest which have pronounced repulsive component belong to this universality class.

cond-mat.stat-mech↗
arXiv2001

Anomalous anapole moment of an exotic nucleus

Using the information on the nuclear structure of exotic neutron-rich halo nucleus $^{11}$Be, we evaluate the parity violating anapole moment in its ground state. The resulting value $κ(^{11}$Be)$=0.17$ is fifteen times bigger than the typical value of the anapole moment of a normal nucleus of the same mass, and in fact exceeds by few times anapole moments of any known neutron-odd nuclei (e.g., kappa(^{11}Be) > 2|κ(^{207}Pb)|. It is also few times bigger than the neutral current contribution to the lepton-nucleus interaction.

nucl-th↗
arXiv2001

Generalized yrast states of a Bose condensate in harmonic trap for a universality class of repulsive interactions

For a system of N bosons in a 2d harmonic trap with frequency omega, interacting via repulsive forces V<<omega, we develop supersymmetric method to find the lowest energy states of rotating Bose condensate as function of two quantum numbers, the total angular momentum and the angular momentum of internal excitations (generalized yrast states). The energies of these condensed vortex states are expressed through the single two-body matrix element of interaction V. A broad universality class of the repulsive interactions for which these results hold is described by a simple integral condition on V. It includes Gaussian, delta-function and log-Coulomb forces.

cond-mat↗
arXiv1999

SU(2,1) Dynamics of Multiple Giant Dipole Resonance Coulomb Excitation

We construct a three-dimensional analytically soluble model of the nonlinear effects in Coulomb excitation of multiphonon Giant Dipole Resonances (GDR) based on the SU(2,1) algebra. The full 3-dimensional model predicts further enhancement of the Double GDR (DGDR) cross sections at high bombarding energies. Enhancement factors for DGDR measured in thirteen different processes with various projectiles and targets at different bombarding energies are well reproduced with the same value of the nonlinearity parameter with the exception of the anomalous case of $^{136}$Xe which requires a larger value.

nucl-th↗
arXiv1999

Giant Resonances in Coulomb Excitations of Relativistic Ions

We propose a soluble model to incorporate the nonlinear effects in the transition probabilities of the multiphonon Giant Dipole Resonances based on the SU(1,1) algebra. Analytical expressions for the multi-phonon transition probabilities are derived. For reasonably small magnitude of nonlinearity $x\simeq 0.1-0.2$ enhancement factor for the Double Giant Resonance excitation probabilities and the cross sections %in relativistic ion collisions reaches values $1.3-2$ compatible with experimental data.

nucl-th↗
arXiv1999

Enhancement of parity violating mixing in halo nuclei and the problem of neutron weak parity nonconserving potential constant

We consider the Parity Nonconserving (PNC) mixing in the ground state of exotic (halo) nuclei caused by the PNC weak interaction between outer neutron and nucleons within nuclear interior. For the nucleus $^{11}Be$ as an example of typical nucleus with neutron halo, we use analytical model for the external neutron wave functions to estimate the scale of the PNC mixing. The amplitude of the PNC mixing in halo state is found to be an order of magnitude bigger than that of typical PNC mixing between the ``normal'' nuclear states in nearby nuclei. The enhanced PNC mixing in halo cloud is proportional to the neutron weak PNC potential constant $g^W_n$ only.

nucl-th↗
arXiv1998

Nonlinear Enhancement of the Multiphonon Coulomb Excitation in Relativistic Heavy Ion Collisions

We propose a soluble model to incorporate the nonlinear effects in the transition probabilities of the multiphonon Giant Dipole Resonances based on the SU(1,1) algebra. Analytical expressions for the multi-phonon transition probabilities are derived. Enhancement of the Double Giant Resonance excitation probabilities in relativistic ion collisions scales as $(2 k +1)(2k)^{-1}$ for the degree of nonlinearity $(2k)^{-1}$ and is able to reach values $1.5-2$ compatible with experimental data. The enhancement factor is found to decrease with increasing bombarding energy. [KEYWORDS: Relativistic Heavy Ion Collisions,Double Giant Resonance]

nucl-th↗
arXiv1997

Renormalization of the one-body off-diagonal Coulomb field in nuclei

Isospin violation effects in nuclei are investigated within a microscopic approach which takes into account the influence of the residual strong interaction on the Coulomb interaction. The renormalization of the off-diagonal Coulomb field acting within a nucleus, by the residual strong interaction is calculated analytically in a simplified RPA. From the expression for the suppression coefficient of the isospin violating part of the Coulomb field, the isospin violating spreading widths of isobaric analog states are derived. The resulting reduction of the width is in agreement with the data on the isospin symmetry restoration and with some earlier evaluations of the isospin violating spreading widths.

nucl-th↗
arXiv1997

Renormalization of the P- and T-odd nuclear potentials by the strong interaction and enhancement of P-odd effective field

Approximate analytical formulas for the self-consistent renormalization of P,T-odd and P-odd weak nuclear potentials by the residual nucleon-nucleon strong interaction are derived. The contact spin-flip nucleon-nucleon interaction reduces the constant of the P,T-odd potential 1.5 times for the proton and 1.8 times for the neutron. Renormalization of the P-odd potential is caused by the velocity dependent spin-flip component of the strong interaction. In the standard variant of $π+ ρ$-exchange, the conventional strength values lead to anomalous enhancement of the P-odd potential. Moreover, the $π$-meson exchange contribution seems to be large enough to generate an instability (pole) in the nuclear response to a weak potential.

nucl-th↗
arXiv1997

Matrix Elements between Nuclear Compound States and Dynamical Enhancement of the Weak Interaction

A method to calculate the mean squared matrix element of weak interaction between compound states is developed. The result is expressed in terms of matrix elements of the nucleon-nucleon strong and weak interactions times the Fermi distribution functions at finite temperature. Numerical calculations for $^{233}$Th are in excellent agreement with recent measurements of parity nonconservation effects in neutron capture. In fact, our calculations prove that the factor of dynamical enhancement (ratio of compound-nucleus effect to single-particle one) really exceeds 100, thus making it unnesessary to assume a value of the weak constant bigger than standard one ($g\simeq 10^{8} ε\sim 1÷4$).

nucl-th↗
arXiv1997

Neutrino-nucleus reactions on ^{12}C and ^{16}O

Exclusive and inclusive $(ν_μ, μ^-), (ν_e, e^-)$ cross-sections and $μ^-$-capture rates are calculated for ^{12}C and ^{16}O using the consistent random phase approximation (RPA) and pairing model. After a pairing correction is introduced to the RPA results the flux-averaged theoretical $(ν_μ, μ^-), (ν_e, e^-)$ cross-sections and $μ^-$-capture rates in $^{12}$C are in good agreement with experiment. In particular when one takes into account the experimental error bars, the recently measured range of values for the $(ν_μ, μ^-)$ cross-section is in agreement with the present theoretical results. Predictions of $(ν_μ, μ^-)$ and $(ν_e, e^-)$ cross-sections in ^{16}O are also presented.

nucl-th↗
arXiv1996

Structure of Low-Energy Collective $0^{-}$-States in Doubly Magic Nuclei and Matrix Elements of the P-odd and P- and T-odd Weak Interaction

The structure of the collective low-energy $J^π=0^{-}$ (T=0 and T=1) modes is studied for a doubly magic nucleus in a schematic analytic model of RPA. The $0^{-}$ phonon states ($T= 0,1$) lie at energies $E_{T=0}(0^{-}) \alt ω$ and $E_{T=1}(0^{-}) > ω$, where $ω$ is the oscillator frequency. The matrix elements of P-odd and P- and T-odd weak one-body potentials connecting the ground state to these $0^{-}$-states, $W_{coll}$, are enhanced by the factor $\sim 2 (\fracω{E})^{1/2}A^{1/3} \sim 10$ as compared to the single-particle value $w_{sp}$ what can result in values $|W_{coll}| \sim 20-30 eV$ if standard values of DDH parameters are used for $w_{sp}$. Similar enhancement arises in the P- and T-odd case.

nucl-th↗
arXiv1995

Limits of Time-Reversal Violating Interaction from Compound Nuclear Experiments

Mean square matrix elements of the time reversal invariance violating (TRIV) interaction between the compound nuclear states are calculated within the statistical model, using the explicit form of the TRIV interaction via the $ρ$-meson exchange. From the comparison of the calculated values with the data known for $p+ ^{27}Al \Leftrightarrow ^{24}Mg + α$ reaction, and for $γ$-correlation measurements in $^{113}Cd(n,γ)^{114}Cd$ process, the bounds on the TRIV constant are obtained ${\bar g}_ρ \alt 1.8 \times 10^{-2}$ and ${\bar g}_ρ \alt 1.1 \times 10^{-2}$. The sensitivity of the recently proposed detailed balance test experiments on isolated resonances in $^{32}S$ to the value of ${\bar g}_ρ$ is shown to be as high as to reach values ${\bar g}_ρ \sim 10^{-4}$.

nucl-th↗
arXiv1994

Effects of T- and P-odd weak nucleon interaction in nuclei: renormalizations due to residual strong interaction, matrix elements between compound states and their correlations with P-violating matrix elements

Manifestations of P-,T-odd weak interaction between nucleons in nucleus are considered. Renormalization of this interaction due to residual strong interaction is studied. Mean squared matrix elements of P-,T-odd weak interaction between compound states are calculated. Correlators between P-,T-odd and P-odd, T-even weak interaction matrix elements between compound states are considered and estimates for these quantities are obtained.

nucl-th↗
arXiv1994

Induced Parity Nonconserving Interaction and Enhancement of Two-Nucleon Parity Nonconserving Forces

Two-nucleon parity nonconserving (PNC) interaction induced by the single-particle PNC weak potential and the two-nucleon residual strong interaction is considered. An approximate analytical formula for this Induced PNC Interaction (IPNCI) between proton and neutron is derived ($Q({\bf r} {\bf σ}_{p} \times {\bf σ}_{n}) δ({\bf r}_{p}-{\bf r}_{n})$), and the interaction constant is estimated. As a result of coherent contributions from the nucleons to the PNC potential, IPNCI is an order of magnitude stronger ($\sim A^{1/3}$) than the residual weak two-nucleon interaction and has a different coordinate and isotopic structure (e.g., the strongest part of IPNCI does not contribute to the PNC mean field). IPNCI plays an important role in the formation of PNC effects, e.g., in neutron-nucleus reactions. In that case, it is a technical way to take into account the contribution of the distant (small) components of a compound state which dominates the result. The absence of such enhancement ($\sim A^{1/3}$) in the case of T- and P-odd interaction completes the picture.

nucl-th↗