arXiv subjects

M. Yu. Kuchiev

Publications and source records attributed to M. Yu. Kuchiev.

At least 37 records · Page 2Linked to original sources

arXiv2002

QED radiative corrections to parity nonconservation in heavy atoms

The self-energy and vertex QED radiative corrections (Z alpha^2 f(Z alpha)) are shown to give a large negative contribution to the parity nonconserving (PNC) amplitude in heavy atoms. The correction -0.7(2)% found for the 6s-7s PNC amplitude in Cs brings the experimental result for this transition into agreement with the standard model. The calculations are based on a new identity that expresses the radiative corrections to the PNC matrix element via corrections to the energy shifts induced by the finite nuclear size.

hep-ph↗

arXiv2002

Influence of perturbations on the electron wave function inside the nucleus

A variation of the valence electron wave function inside a nucleus induced by a perturbative potential is expressed in terms of the potential momenta. As an application we consider QED vacuum polarization corrections due to the Uehling and Wichmann-Kroll potentials to the weak interaction matrix elements.

hep-ph↗

arXiv2001

A boost to low energy nuclear reactions from preliminary elastic collisions (Carambole collisions)

In conventional nuclear experiments a beam of accelerated nuclei collides with a target nucleus that is surrounded by other nuclei in a molecule, in condensed matter, or in a plasma environment. It is shown that for low collision energies possible nuclear reactions (including deuterium fusion) are strongly boosted by the environment. The effect originates from a chain of preliminary three elastic collisions which transform the projectile-target experiment into one with colliding beams. Firstly, the projectile-target pair of nuclei undergo elastic scattering in which the projectile shares its energy and momentum with the target nucleus. Then the projectile and target nuclei collide with different heavy nuclei from the environment. These latter collisions change the velocities of the target and projectile nuclei and set them again on the collision course. Finally, the same pair of nuclei collide inelastically, this time giving rise to the nuclear reaction. The increased energy of the target nucleus increases the relative velocity up to sqrt 2 times, resulting in a drastic exponential increase of the probability to penetrate the Coulomb barrier and therefore sharply increasing the likelihood of the nuclear reaction. Applications to laser-induced fusion are discussed.

nucl-th↗

arXiv2000

"Colliding beam" enhancement mechanism of deuteron-deuteron fusion reactions in matter

We suggest a ``ping-pong'' mechanism of enhancement for fusion reactions between a low energy external deuteron beam and the deuterons in a condensed matter or molecular target. The mechanism is based on the possibility of acceleration of a target deuteron by the Coulomb field of a projectile deuteron with its subsequent rebound from a heavy atom in matter and the following fusion of the two deuterons moving towards each other. This effectively converts the fixed target process into a colliding beam reaction. In a simple limiting case this reduces the negative penetrability exponent by a factor of $\sqrt{2}$. We also discuss a contribution given by ``zero oscillations'' of a bound target deuteron. The proposed mechanism is expected to be efficient in compounds with target deuterons localized in the vicinity of heavy atoms.

nucl-th↗

arXiv2000

Atomic antenna mechanism in HHG and ATI

This paper reviews recent development of the atomic antenna, a theoretical framework which describes a number of laser-induced multiphoton phenomena in atoms, in particular in High Harmonic Generation and in Above Threshold Ionization. The paper presents a progress report made at the conference "Atoms, molecules and quantum dots in laser fields: fundamental processes", PISA, Italy, June 12-16, 2000

physics.atom-ph↗

arXiv2000

Comment on "Degenerate Wannier Theory for Multiple Ionization"

Recent Letter of T.Pattard and J.M.Rost (Phys.Rev.Lett 80, 5081 (1998)) suggests that there exist logarithmic corrections to the near threshold cross section for the processes of break up of a particle into several charged fragments. This comment shows that it is incorrect, the logarithmic terms never exist. The cross section for all processes behaves as some power of the above-threshold energy, similarly to the known Wannier problem.

physics.atom-ph↗

arXiv2000

Effective ATI Channels in High Harmonic Generation

Harmonic generation by an atom in a laser field is described by the three-step mechanism as proceeding via above-threshold ionization (ATI) followed by the electron propagation in the laser-dressed continuum and the subsequent laser assisted recombination (LAR). An amplitude of harmonic production is given by the coherent sum of contributions from different intermediate ATI channels labeled by the number m of absorbed laser photons. The range of m-values that gives substantial contribution is explored and found to be rather broad for high harmonic generation. The coherence effects are of crucial importance being responsible for the characteristic pattern of harmonic intensities with a plateau domain followed by a cutoff region. Due to multiphoton nature of the process, an efficient summation of m-contributions can be carried out in the framework of the saddle point method. The saddle points correspond to some complex-valued labels m=m_c associated with the intermediate effective ATI channels in the three-step harmonic generation process. The advantage of this approach stems from the fact that summation over large number of conventional ATI m-channels is replaced by summation over small number of effective m_c-channels. The equation governing m_c has a transparent physical meaning: the electron ejected from the atom on the first (ATI) stage should return to the core to make LAR possible. The calculated rates are in good agreement with the results obtained by other approaches.

physics.atom-ph↗

arXiv1999

Multiphoton radiative recombination of electron assisted by laser field

In the presence of an intensive laser field the radiative recombination of the continuum electron into an atomic bound state generally is accompanied by absorption or emission of several laser quanta. The spectrum of emitted photons represents an equidistant pattern with the spacing equal to the laser frequency. The distribution of intensities in this spectrum is studied employing the Keldysh-type approximation, i.e. neglecting interaction of the impact electron with the atomic core in the initial continuum state. Within the adiabatic approximation the scale of emitted photon frequencies is subdivided into classically allowed and classically forbidden domains. The highest intensities correspond to emission frequencies close to the edges of classically allowed domain. The total cross section of electron recombination summed over all emitted photon channels exhibits negligible dependence on the laser field intensity.

physics.atom-ph↗

arXiv1999

Possible mechanism of the fractional conductance quantization in a one-dimensional constriction

As it is well known there may arise situations when an interaction between electrons is attractive. A weak attraction should manifest itself strongly in 1D systems, since it can create two-electron bound states. This paper interprets the 0.7 $(2e^2/h)$ conductance structure, observed recently in a one-dimensional constriction, as a manifestation of two-electron bound states formed in a barrier saddle-point. The value 0.75 $(2e^2/h)$ follows naturally from the 3:1 triplet-singlet statistical weight ratio for the two-electron bound states, if the triplet energy is lower. Furthermore, the value 0.75 has to be multiplied by the probability T of the bound state formation during adiabatic transmission of two electrons into 1D channel ($T\simeq 1$). If the binding energy is larger than the sub-band energy spacing the 0.7 structure can be seen even when the integer steps are smeared away by the temperature. Bound states of several electrons, if they exist, may give different steps at 1/2, 5/16, 3/16 etc in the conductance. The latter results are sensitive to the length of 1D system and the electron density at the barrier. It is not excluded that the fractional conductance quantization may also appear for a repulsive interaction between electrons. In this case the electron level splitting is due to the exchange interaction with two nearest neighbors in a 1D Wigner crystal.

cond-mat.mes-hall↗

arXiv1999

Gravity and instantons

Conventional non-Abelian SO(4) gauge theory is able to describe gravity provided the gauge field possesses a specific polarized vacuum state in which the instantons have a preferred orientation. Their orientation plays the role of the order parameter for the polarized phase of the gauge field. The interaction of a weak and smooth gauge field with the polarized vacuum is described by an effective long-range action which is identical to the Hilbert action of general relativity. In the classical limit this action results in the Einstein equations of general relativity. Gravitons appear as the mode describing propagation of the gauge field which strongly interacts with the oriented instantons. The Newton gravitational constant describes the density of the considered phase of the gauge field. The radius of the instantons under consideration is comparable with the Planck radius.

hep-th↗

arXiv1999

Quantum theory of a high harmonic generation as a three-step process

Fully quantum treatment explicitly presents the high harmonic generation as a three-step process: (i) above threshold ionization (ATI) is followed by (ii) electron propagation in a laser-dressed continuum. Subsequently (iii) stimulated (or laser assisted) recombination brings the electron back into the initial state with emission of a high-energy photon. Contributions of all ATI channels add up coherently. All three stages of the process are described by simple, mostly analytical expressions that allow a detailed physical interpretation. A very good quantitative agreement with the previous calculations on the harmonic generation by H-minus ion is demonstrated, thus supplementing the conceptual significance of the theory with its practical efficiency. The virtue of the present scheme is further supported by a good accord between the calculations in length and velocity gauges for the high-energy photon.

physics.atom-ph↗

arXiv1999

Two-photon detachment of electrons from halogen negative ions

Absolute two-photon detachment cross sections and photoelectron angular distribution are calculated for halogen negative ions within lowest-order perturbation theory. The Dyson equation method is used to obtain the outer np ground-state wave functions with proper asymptotic behavior exp (-k r), corresponding to correct (experimental) binding energies E=k^2/2. The latter is crucial for obtaining correct absolute values of the multiphoton cross sections (Gribakin and Kuchiev 1997 Phys. Rev.A55 3760). Comparisons with previous calculations and experimental data are performed.

physics.atom-ph↗

arXiv1999

Strong dependence of multiphoton detachment rates on the asymptotic behaviour of the ground-state wave function

Two-photon detachment from the F-minus negative ion is investigated within the lowest order of perturbation theory. We show that in accordance with the adiabatic theory a proper asymptotic behaviour of the 2p bound state wave function is crucial for obtaining correct absolute values of the multiphoton detachment cross sections. We find that the latter are substantially higher than it was previously believed.

physics.atom-ph↗

arXiv1999

Quantum Theory of High Harmonic Generation via Above Threshold Ionization and Stimulated Recombination

Fully quantum treatment explicitly presents the high harmonic generation as a three-stage process: above threshold ionization (ATI) is followed by the continuum electron propagation in a laser field and subsequent stimulated recombination back into the initial state. The contributions of all ATI channels add up coherently. All three stages of the process are described by simple, mostly analytical expressions. A very good quantitative agreement with the previous calculations on the harmonic generation by H$^-$ ion is demonstrated, thus supplementing the conceptual significance of the theory with its practical efficiency.

physics.atom-ph↗

arXiv1998

Adiabatic Theory of Electron Detachment from Negative Ions in Two-Color Laser Field

Negative ion detachment in bichromatic laser field is considered within the adiabatic theory. The latter represents a recent modification of the famous Keldysh model for multiphoton ionization which makes it quantitatively reliable. We calculate angular differential detachment rates, partial rates for particular ATD (Above Threshold Detachment) channels and total detachment rates for the Hydrogen ion in a bichromatic field with 1:3 frequency ratio and various phase differences. Reliability of the present, extremely simple approach is testified by comparison with much more elaborate earlier calculations.

physics.atom-ph↗

arXiv1998

Can gravity appear due to polarization of instantons in the SO(4) gauge theory?

Conventional non-Abelian SO(4) gauge theory is able to describe gravity provided the gauge field possesses a specific polarized vacuum state. In this vacuum the instantons and anti-instantons have a preferred direction of orientation. Their orientation plays the role of the order parameter for the polarized phase of the gauge field. The interaction of a weak and smooth gauge field with the polarized vacuum is described by an effective long-range action which is identical to the Hilbert action of general relativity. In the classical limit this action results in the Einstein equations of general relativity. Gravitational waves appear as the mode describing propagation of the gauge field which strongly interacts with the oriented instantons. The Newton gravitational constant describes the density of the considered phase of the gauge field. The radius of the instantons under consideration is comparable with the Planck radius.

hep-th↗

arXiv1998

Threshold Laws for the Break-up of Atomic Particles into Several Charged Fragments

The processes with three or more charged particles in the final state exhibit particular threshold behavior, as inferred by the famous Wannier law for (2e + ion) system. We formulate a general solution which determines the threshold behavior of the cross section for multiple fragmentation. Applications to several systems of particular importance with three, four and five leptons (electrons and positrons) in the field of charged core; and two pairs of identical particles with opposite charges are presented. New threshold exponents for these systems are predicted, while some previously suggested threshold laws are revised.

physics.atom-ph↗

arXiv1997

Electron detachment from negative ions in bichromatic laser field

Negative ion detachment in two-colour laser field is considered within the recent modification of Keldysh model which makes it quantitatively reliable. The general approach is illustrated by calculation of angular differential detachment rates, partial rates for particular ATD (Above Threshold Detachment) channels and total detachment rates for H$^-$ ion in bichromatic field with 1:2 frequency ratio. Both perturbative and strong field regimes are examined. Polar asymmetry and phase effects are quantitatively characterized with some new features revealed. Phase effects are found to result in a huge anisotropy factor $\sim 10^3$ in the electron angular distribution in the perturbative regime.

physics.atom-ph↗