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M. I. Krivoruchenko

Publications and source records attributed to M. I. Krivoruchenko.

At least 55 records · Page 3Linked to original sources
arXiv2011

Resonance enhancement of neutrinoless double electron capture

The process of neutrinoless double electron capture ($0ν$ECEC) is revisited for those cases where the two participating atoms are nearly degenerate in mass. The theoretical framework is the formalism of an oscillation of two atoms with different total lepton number (and parity), one of which can be in an excited state so that mass degeneracy is realized. In such a case and assuming light Majorana neutrinos, the two atoms will be in a mixed configuration with respect to the weak interaction. A resonant enhancement of transitions between such pairs of atoms will occur, which could be detected by the subsequent electromagnetic de-excitation of the excited state of the daughter atom and nucleus. Available data of atomic masses, as well as nuclear and atomic excitations are used to select the most likely candidates for such resonant $0ν$ECEC transitions. Assuming an effective mass for the Majorana neutrino of 1 eV, some half-lives are predicted to be as low as $10^{22}$ years in the unitary limit. It is argued that, in order to obtain more accurate predictions for the $0ν$ECEC half-lives, precision mass measurements of the atoms involved are necessary, which can readily be accomplished by today's high precision Penning traps. Further advancements also require a better understanding of high-lying excited states of the final nuclei (i.e. excitation energy, angular momentum and parity) and the calculation of the nuclear matrix elements.

hep-ph↗
arXiv2011

Possibility of narrow resonances in nucleon-nucleon channels

Compound states manifest themselves as bound states, resonances, or primitives, and their character is determined by their interaction with the continuum. If the interaction experiences a perturbation, a compound state can change its manifestation. Phase analysis of nucleon-nucleon scattering indicates the existence of primitives in the 3S1, 1S0, and 3P0 channels. Electromagnetic interaction can shift primitives from the unitary cut, turning them into narrow resonances. We evaluate this effect on the 1S0 proton-proton scattering channel within the framework of the Simonov-Dyson model. We show that electromagnetic interaction turns a primitve with a mass of 2000 MeV into a dibaryon resonance of approximately the same mass and a width of 260 keV. Narrow resonances of a similar nature may occur in other nucleon-nucleon channels. Experimental confirmation of the existence of narrow resonances would have important implications for the theory of nucleon-nucleon interaction.

nucl-th↗
arXiv2010

Remarks on the origin of Castillejo-Dalitz-Dyson poles

Castillejo-Dalitz-Dyson (CDD) poles are known to be connected with bound states and resonances. We discuss a new type of CDD pole associated with primitives i.e., poles of the P matrix that correspond to zeros of the D function on the unitary cut. Low's scattering equation is generalized for amplitudes with primitives. The relationship between the CDD poles and the primitives is illustrated by a description of the S-wave nucleon-nucleon phase shifts.

nucl-th↗
arXiv2010

Nuclear matter at high density: Phase transitions, multiquark states, and supernova outbursts

Phase transition from hadronic matter to quark-gluon matter is discussed for various regimes of temperature and baryon number density. For small and medium densities, the phase transition is accurately described in the framework of the Field Correlation Method, whereas at high density predictions are less certain and leave room for the phenomenological models. We study formation of multiquark states (MQS) at zero temperature and high density. Relevant MQS components of the nuclear matter can be described using a previously developed formalism of the quark compound bags (QCB). Partial-wave analysis of nucleon-nucleon scattering indicates the existence of 6QS which manifest themselves as poles of $P$-matrix. In the framework of the QCB model, we formulate a self-consistent system of coupled equations for the nucleon and 6QS propagators in nuclear matter and the G-matrix. The approach provides a link between high-density nuclear matter with the MQS components and the cumulative effect observed in reactions on the nuclei, which requires the admixture of MQS in the wave functions of nuclei kinematically. 6QS determine the natural scale of the density for a possible phase transition into the MQS phase of nuclear matter. Such a phase transition can lead to dynamic instability of newly born protoneutron stars and dramatically affect the dynamics of supernovae. Numerical simulations show that the phase transition may be a good remedy for the triggering supernova explosions in the spherically symmetric supernova models. A specific signature of the phase transition is an additional neutrino peak in the neutrino light curve. For a Galactic core-collapse supernova, such a peak could be resolved by the present neutrino detectors. The possibility of extracting the parameters of the phase of transition from observation of the neutrino signal is discussed also.

hep-ph↗
arXiv2009

Once more on electromagnetic form factors of nucleons in extended vector meson dominance model

Extended vector meson dominance model, that allows to describe the electromagnetic form factors of nucleons obeying the asymptotic quark counting rule prescriptions and contains the minimal number of free parameters, is presented. We get a reasonable fit of form factors over experimentally available space-like region of momentum transfer and get also reasonable results in the time-like region.

hep-ph↗
arXiv2009

Constraints for weakly interacting light bosons from existence of massive neutron stars

Theories beyond the standard model include a number of new particles some of which might be light and weakly coupled to ordinary matter. Such particles affect equation of state of nuclear matter and can shift admissible masses of neutron stars to higher values. The internal structure of neutron stars is modified provided the ratio between coupling strength and mass squared of a weakly interacting light boson is above $g^2/μ^2 \sim 25 ~\mathrm{GeV}^{-2}$. We provide limits on the couplings with the strange sector, which cannot be achieved from laboratory experiments analysis. When the couplings to the first family of quarks is considered the limits imposed by the neutron stars are not more stringent than the existing laboratory ones. The observations on neutron stars give evidence that equation of state of the $β$-equilibrated nuclear matter is stiffer than expected from many-body theory of nuclei and nuclear matter. A weakly interacting light vector boson coupled predominantly to the second family of the quarks can produce the required stiffening.

hep-ph↗
arXiv2008

Dilepton production in heavy-ion collisions with in-medium spectral functions of vector mesons

The in-medium spectral functions of $ρ$ and $ω$ mesons and the broadening of the nucleon resonances at finite baryon density are calculated self-consistently by combining a resonance dominance model for the vector meson production with an extended vector meson dominance model. The influence of the in-medium modifications of the vector meson properties on the dilepton spectrum in heavy-ion collisions is investigated. The dilepton spectrum is generated for the C+C reaction at 2.0$A$ GeV and compared with recent HADES Collaboration data. The collision dynamics is then described by the Tübingen relativistic quantum molecular dynamics transport model. We find that an iterative calculation of the vector meson spectral functions that takes into account the broadening of the nucleon resonances due to their increased in-medium decay branchings is convergent and provides a reasonable description of the experimental data in the mass region $0.45\leq M \leq 0.75$ GeV. On the other side, the theoretical calculations slightly underestimate the region $m_π\leq M \leq 0.4$ GeV. Popular in-medium scenarios such as a schematic collisional broadening and dropping vector mesons masses are discussed as well.

nucl-th↗
arXiv2008

Decays, contact P-wave interactions and hyperfine structure in Omega- exotic atoms

Contact $P$-wave interactions connected to the Larmor interaction of a magnetic dipole and Thomas spin precession in the filed of an electric quadrupole are described and their implications for spectroscopy of exotic $Ω^{-}$-atoms are studied. In order to evaluate the magnitude of the contact $P$-wave interactions as compared to the conventional long-range interactions and the sensitivity of spectroscopic data to the $Ω^{-}$-hyperon quadrupole moment, we consider $2P$ states of $Ω^{-}$ atoms formed with light stable nuclei with spins $I \geq 1/2$ and atomic numbers $Z \leq 10$. The energy level splitting caused by the contact interactions is 2-5 orders of magnitude smaller than the conventional long-range interactions. Strong decay widths of $pΩ^{-}$ atoms due to reactions $pΩ^{-} \to ΛΞ^{0}$ and $pΩ^{-} \to ΣΞ$, induced by $t$-channel kaon exchanges, are calculated. $Ω^{-}$ atoms formed with the light nuclei have strong widths 5-6 orders of magnitude higher than splitting caused by the contact interactions. The low-$L$ pattern in the energy spectra of intermediate- and high-$Z$ $Ω^{-}$ atoms thus cannot be observed. The $Ω^{-}$ quadrupole moment can be measured by observing $X$-rays from circular transitions between high-$L$ levels in $Ω^{-}$ exotic atoms. The effect of strong interactions in $^{208}$Pb$Ω^{-}$ atoms is negligible starting from $L \sim 10$. The contact $P$-wave interactions exist in ordinary atoms and $μ$-meson atoms.

nucl-th↗
arXiv2007

Comment on "Dynamics of nuclear fluid. VIII. Time-dependent Hartree-Fock approximation from a classical point of view"

The phase-space paths introduced by Cheuk-Yin Wong in Phys. Rev.C25, 1460 (1982) and discussed recently in the literature can be used for calculation of evolution of the Wigner function to first order in the time increments only. The first-order solutions are helpful to determine the phase-space Green function in the framework of the phase-space path integral method.

hep-ph↗
arXiv2007

Semiclassical expansion of quantum characteristics for many-body potential scattering problem

In quantum mechanics, systems can be described in phase space in terms of the Wigner function and the star-product operation. Quantum characteristics, which appear in the Heisenberg picture as the Weyl's symbols of operators of canonical coordinates and momenta, can be used to solve the evolution equations for symbols of other operators acting in the Hilbert space. To any fixed order in the Planck's constant, many-body potential scattering problem simplifies to a statistical-mechanical problem of computing an ensemble of quantum characteristics and their derivatives with respect to the initial canonical coordinates and momenta. The reduction to a system of ordinary differential equations pertains rigorously at any fixed order in $\hbar$. We present semiclassical expansion of quantum characteristics for many-body scattering problem and provide tools for calculation of average values of time-dependent physical observables and cross sections. The method of quantum characteristics admits the consistent incorporation of specific quantum effects, such as non-locality and coherence in propagation of particles, into the semiclassical transport models. We formulate the principle of stationary action for quantum Hamilton's equations and give quantum-mechanical extensions of the Liouville theorem on the conservation of phase-space volume and the Poincaré theorem on the conservation of $2p$ forms. The lowest order quantum corrections to the Kepler periodic orbits are constructed. These corrections show the resonance behavior.

nucl-th↗
arXiv2007

Weyl's symbols of Heisenberg operators of canonical coordinates and momenta as quantum characteristics

The knowledge of quantum phase flow induced under the Weyl's association rule by the evolution of Heisenberg operators of canonical coordinates and momenta allows to find the evolution of symbols of generic Heisenberg operators. The quantum phase flow curves obey the quantum Hamilton's equations and play the role of characteristics. At any fixed level of accuracy of semiclassical expansion, quantum characteristics can be constructed by solving a coupled system of first-order ordinary differential equations for quantum trajectories and generalized Jacobi fields. Classical and quantum constraint systems are discussed. The phase-space analytic geometry based on the star-product operation can hardly be visualized. The statement "quantum trajectory belongs to a constraint submanifold" can be changed e.g. to the opposite by a unitary transformation. Some of relations among quantum objects in phase space are, however, left invariant by unitary transformations and support partly geometric relations of belonging and intersection. Quantum phase flow satisfies the star-composition law and preserves hamiltonian and constraint star-functions.

quant-ph↗
arXiv2006

Density resummation of perturbation series in a pion gas to leading order in chiral perturbation theory

The mean field (MF) approximation for the pion matter, being equivalent to the leading ChPT order, involves no dynamical loops and, if self-consistent, produces finite renormalizations only. The weight factor of the Haar measure of the pion fields, entering the path integral, generates an effective Lagrangian $δ\mathcal{L}_{H}$ which is generally singular in the continuum limit. There exists one parameterization of the pion fields only, for which the weight factor is equal to unity and $δ\mathcal{L}_{H}=0$, respectively. This unique parameterization ensures selfconsistency of the MF approximation. We use it to calculate thermal Green functions of the pion gas in the MF approximation as a power series over the temperature. The Borel transforms of thermal averages of a function $\mathcal{J}(χ^αχ^α)$ of the pion fields $χ^α$ with respect to the scalar pion density are found to be $\frac{2}{\sqrtπ}\mathcal{J}(4t)$. The perturbation series over the scalar pion density for basic characteristics of the pion matter such as the pion propagator, the pion optical potential, the scalar quark condensate $<{\bar{q}}q>$, the in-medium pion decay constant ${\tilde{F}}$, and the equation of state of pion matter appear to be asymptotic ones. These series are summed up using the contour-improved Borel resummation method. The quark scalar condensate decreases smoothly until $T_{max}\simeq 310$ MeV. The temperature $T_{max}$ is the maximum temperature admissible for thermalized non-linear sigma model at zero pion chemical potentials. The estimate of $T_{max}$ is above the chemical freeze-out temperature $T\simeq 170$ MeV at RHIC and above the phase transition to two-flavor quark matter $T_{c} \simeq 175$ MeV, predicted by lattice gauge theories.

hep-ph↗
arXiv2006

Probing in-medium vector mesons by dileptons at heavy-ion colliders

An introduction to physics of in-medium hadrons with special emphasis towards modification of vector meson properties in dense nuclear matter is given. We start from remarkable analogy between the in-medium behavior of atoms in gases and hadrons in nuclear matter. Modifications of vector meson widths and masses can be registered experimentally in heavy-ion collisions by detecting dilepton spectra from decays of nucleon resonances and light unflavored mesons including $ρ$- and $ω$-mesons. Theoretical schemes for description of the in-medium hadrons are reviewed and recent experimental results of the NA60 and HADES collaborations on the dilepton production are discussed.

nucl-th↗
arXiv2006

Moyal dynamics of constraint systems

Quantization of constraint systems within the Weyl-Wigner-Groenewold-Moyal framework is discussed. Constraint dynamics of classical and quantum systems is reformulated using the skew-gradient projection formalism. The quantum deformation of the Dirac bracket is generalized to match smoothly the classical Dirac bracket in and outside of the constraint submanifold in the limit $\hbar \to 0$.

hep-th↗
arXiv2006

Underlying gauge symmetries of second-class constraints systems

Gauge-invariant systems in unconstrained configuration and phase spaces, equivalent to second-class constraints systems upon a gauge-fixing, are discussed. A mathematical pendulum on an $n-1$-dimensional sphere $S^{n-1}$ as an example of a mechanical second-class constraints system and the O(n) non-linear sigma model as an example of a field theory under second-class constraints are discussed in details and quantized using the existence of underlying dilatation gauge symmetry and by solving the constraint equations explicitly. The underlying gauge symmetries involve, in general, velocity dependent gauge transformations and new auxiliary variables in extended configuration space. Systems under second-class holonomic constraints have gauge-invariant counterparts within original configuration and phase spaces. The Dirac's supplementary conditions for wave functions of first-class constraints systems are formulated in terms of the Wigner functions which admit, as we show, a broad set of physically equivalent supplementary conditions. Their concrete form depends on the manner the Wigner functions are extrapolated from the constraint submanifolds into the whole phase space.

hep-th↗
arXiv2006

$D$-mesons and charmonium states in hot pion matter

We calculate the in-medium $D$ meson self-energies in a hot pion gas induced by resonance interactions with pions. The appropriate resonances in the {\it s},~ {\it p} and {\it d} waves of the $D$ meson-pion pair are represented by low lying scalar, vector and tensor $D^*$ mesons. At temperatures around 200 MeV the D-meson mass drops by $30~ \rm {MeV}$ and the scattering width grows up to $60~ \rm {MeV}$. Similar medium effects are found for the $D^*$ vector mesons. This opens and/or enhances the decay and/or dissociation channels of the charmonium states $Ψ^\prime$, $χ_c$ and $J/Ψ$ to $D \bar D,~D^* \bar D,~D \bar D^* ,~D^* \bar D^*$ pairs in pion matter.

nucl-th↗