Resonant mechanism of axion photoproduction in a magnetized electron gas

It was shown that the contribution of diagrams with electron-positron vacuum excitation in a strong magnetic field B ? B ₀ = m ²/e = 4.41 × 10¹³ G in the Compton mechanism of axion production γe → ae at temperatures on the order of the axion mass exceeds the contribution of the “simple” Compton diagram and the contribution of the neutrino production γe → (ν\(\bar \nu \))e to the radiation power by many orders of magnitude. The conclusion is made on the probable axionic nature of the cold hidden mass of the Universe.     

Effectively two-dimensional mechanism of axion and neutrino bremsstrahlung in the interaction of electrons with nuclei in a magnetic field

Axion and neutrino bremsstrahlung from electrons in the processes $e(Ze) \to e(Ze)a(\nu \bar \nu )$ is considered within the proposed two-dimensional covariant method for calculating Feynman diagrams in an external magnetic field. General expressions for squared matrix elements, as well as for the probability and power of this radiation, are obtained for a nonrelativistic nondegenerate electron gas. The energy scale f _a characteristic of the violation of global Peccei-Quinn symmetry is constrained by comparing the contributions of the above processes to the emissivity of magnetic neutron stars.     

The electromagnetic mechanism of plasmon decay to a neutrino pair in a strongly magnetized electron gas

An expression for the neutrino luminosity of a degenerate electron gas in a strong magnetic field via plasmon decay to a neutrino pair due to electromagnetic neutrino moments is derived. The neutrino luminosity of the medium in an electromagnetic reaction channel is shown to be comparable with the luminosity in a weak channel. The relative upper bounds for the effective magnetic neutrino moment are obtained.     

Expansion of an interacting fermi gas

We study the expansion of a dilute ultracold sample of fermions initially trapped in an anisotropic harmonic trap. The expansion of the cloud provides valuable information about the state of the system and the role of interactions. In particular, the time evolution of the deformation of the expanding cloud behaves quite differently depending on whether the system is in the normal or in the superfluid phase. For the superfluid phase, we predict an inversion of the deformation of the sample, similar to what happens with Bose-Einstein condensates. Vice versa, in the normal phase, the inversion of the aspect ratio is never achieved, if the mean field interaction is attractive and collisions are negligible.     

Photoproduction of a neutrino on an electron in a dense magnetized medium

The effect of a strongly magnetized cold plasma on the Compton-like photoproduction of a neutrino on an electron \(\gamma e \to e\nu \bar \nu \) has been considered. The contribution of this process to the neutrino emissivity has been calculated with the inclusion of the dispersion properties of a photon in the medium. A method for the calculation of the emissivity of the process under consideration in terms of the width of the Compton absorption of the photon has been proposed. This method shows that the neutrino emissivity owing to the \(\gamma e \to e\nu \bar \nu \) reaction is significantly modified as compared to the previously reported data.     

Interaction-controlled transport of an ultracold fermi gas

We explore the transport properties of an interacting Fermi gas in a three-dimensional optical lattice. The center of mass dynamics of the atoms after a sudden displacement of the trap minimum is monitored for different interaction strengths and lattice fillings. With increasingly strong attractive interactions the weakly damped oscillation, observed for the noninteracting case, turns into a slow relaxational drift. Tuning the interaction strength during the evolution allows us to dynamically control the transport behavior. Strong attraction between the atoms leads to the formation of local pairs with a reduced tunneling rate. The interpretation in terms of pair formation is supported by a measurement of the number of doubly occupied lattice sites. This quantity also allows us to determine the temperature of the noninteracting gas in the lattice to be as low as (27+/-2)% of the Fermi temperature.     

Diffraction of a superfluid fermi gas by an atomic grating

An atomic grating generated by a pulsed standing-wave laser field is proposed to manipulate the superfluid state in a quantum degenerate gas of fermionic atoms. We show that in the presence of atomic Cooper pairs, the density oscillations of the gas caused by the atomic grating exhibit a much longer coherence time than that in the normal Fermi gas. Our result indicates that the technique of a pulsed atomic grating is a potential candidate to detect the atomic superfluid state in a quantum degenerate Fermi gas.     

Compton effect in and power absorption by an electron gas

An analysis is made of Compton scattering by an electron gas. The power absorption and heating of an electron gas are calculated. The possible measurement of the intensity of intense coherent light beams is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 95–99, September, 1970.     

Synchrotron and annihilation channels for axion production in an external electromagnetic field

We consider axion formation processes in the synchrotron (e ⁻→e ⁻ a) and annihilation (e ⁻ e ⁺→a) channels in a constant crossed field F _μν F^μν=Fμν*F ^μν =0, which approximates constant fields of other configurations in the ultrarelativistic asymptotic limit. The probability and intensity of axion emission are obtained, and we analyze the energy and field asymptotics. A comparison with the characteristic neutrino channel yields the constraints on the axion mass and the energy scale for Peccei-Quinn symmetry breaking. Possible astrophysical applications are discussed. Zh. éksp. Teor. Fiz. 112, 25–31 (July 1997)     

On the thermodynamics of an ideal fermi gas on the lattice at finite density

We study the ideal gas of fermions on a lattice at finite density for both naive and Wilson fermions. Comparing the thermodynamical quantities thus calculated with the known results in the continuum theory, we are led to propose a modification of the naive form of the lattice action, which is same for both the naive and the Wilson fermions. The thermodynamical quantities, calculated by using this form, are shown to have the correct continuum limit.     

The modes of an ultra-cold strongly magnetized charged Bose gas

The modes of a strongly magnetized charged Bose gas are presented for ultra-low temperatures. For longitudinal oscillations propagating parallel to the magnetic field the dispersion relation is found to be dominated by the one-dimensional field-free plasmon dispersion relation as found by Alexandrov, Beere and Kabanov recently in reference [1], while for propagation perpendicular to the magnetic field they are found to be influenced by the cyclotron motion of the particles. Dispersion relations for these modes known as Bernstein modes are given near the cyclotron frequency and its first two harmonics. The dispersion relations for transverse modes in the system are then presented for the cases of photon propagation perpendicular and parallel to the direction of the magnetic field. Received: 3 July 1997 / Revised: 12 August 1997 / Accepted: 4 November 1997     

Finite-temperature phase diagram of a polarized fermi gas in an optical lattice

We present phase diagrams for a polarized Fermi gas in an optical lattice as a function of temperature, polarization, and lattice filling factor. We consider the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO), Sarma or breached pair, and BCS phases, and the normal state and phase separation. We show that the FFLO phase appears in a considerable portion of the phase diagram. The diagrams have two critical points of different nature. We show how various phases leave clear signatures to momentum distributions of the atoms which can be observed after time of flight expansion.     

Spin and dispersion of a massive Dirac neutrino in a magnetized plasma

The total energy shift of a polarized massive Dirac neutrino in an electron–positron plasma in a constant magnetic field is investigated. The calculation in the Feynman gauge is performed for the first time by using the Matsubara temperature Green functions. The dependence of the dispersion relation and the anomalous magnetic moment of the neutrino on the magnetic field strength, spin, energy, direction of motion, neutrino mass, and the plasma parameters is analyzed. The results of investigations for the massive neutrino in the limiting case are compared with those obtained earlier by other authors for the massless left neutrino.     

On the ground state of an impurity in a dilute fermi gas

The system under consideration is a large collection of identical fermions (B), forming a background, into which is inserted a relatively small number of distinct impurity (I) particles. The background is considered to be dilute in the sense that R ? a, where R is the average separation of the B particles, and a is the range of their interaction potential; and the I particles are so dilute with respect to the B particles that I-I interactions can be ignored. The I particles are then all essentially at rest in their ground state. The BB and BI interaction potentials are chosen to be hard cores of the same range a. A series expansion is developed for the ground-state energy of the I particles, and the first four terms are calculated explicitly using two distinct methods, employing Feynman and Goldstone diagrams respectively. It is shown that each method has distinct advantages over the other, and that a judicious combination of both can be used to considerable benefit.     

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应用多光子非线性Compton散射模型和分段电流密度卷积时域有限差分法,将入射光和Compton 散射光作为形成缺陷模的机制,研究了Compton散射对具有单一缺陷模的时变磁化等离子体光子晶体缺陷模的影响.结果表明:与Compton散射前相比,入射光频率低于等离子体频率时,禁带中仍存在明显的缺陷模,其频率随等离子体驰豫时间的增大而缓慢增大;等离子体弛豫时间相等时,等离子体均匀分布的禁带透射系数峰值比Epstein分布时小,两者的缺陷模特征都比较明显,但两者的禁带宽度及缺陷模之间的区别明显减小.     

On some effective mechanism for charmed particle production in neutrino and antineutrino beams

The paper describes an effective mechanism for charmed particle production in neutrino and antineutrino reactions, which consists in production of charmed virtual vector F1-meson in a weak vertex νF1μ (without suppression by the Cabibbo angle) with further strong rescattering of F1-meson on nucleon. This “quasidiffractive” mechanism should make the basic contribution to the production of charmed particles in neutrino experiments basic energies up to some hundreds of GeV. The charmed particles are mainly produced at limited momentum transfers $\text{|q}{}^2\text{| ≈ M}{}^2{}_{\mathrm{<mtext>F</mtext>}}\text{1}$ and with equal cross sections in the neutrino and antineutrino beams.