21,002 research outputs found
On kaonic deuterium. Quantum field theoretic and relativistic covariant approach
We study kaonic deuterium, the bound K^-d state A_(K d). Within a quantum
field theoretic and relativistic covariant approach we derive the energy level
displacement of the ground state of kaonic deuterium in terms of the amplitude
of K^-d scattering for arbitrary relative momenta. Near threshold our formula
reduces to the well-known DGBT formula. The S-wave amplitude of K^-d scattering
near threshold is defined by the resonances Lambda(1405), Sigma(1750) and a
smooth elastic background, and the inelastic channels K^- d -> NY and K^- d ->
NY pion, with Y = Sigma^(+/-), Sigma^0 and Lambda^0, where the final-state
interactions play an important role. The Ericson-Weise formula for the S-wave
scattering length of K^-d scattering is derived. The total width of the energy
level of the ground state of kaonic deuterium is estimated using the
theoretical predictions of the partial widths of the two-body decays A_(Kd) ->
NY and experimental data on the rates of the NY-pair production in the
reactions K^-d -> NY. We obtain Gamma_{1s} = (630 +/-100) eV. For the shift of
the energy level of the ground state of kaonic deuterium we predict
epsilon_(1s) = (353 +/-60)eV.Comment: 73 pages,10 figures, Latex, We have slightly corrected the
contribution of the double scattering. The change of the S-wave scattering
length of K^-d scattering does not go beyond the theoretical uncertainty,
which is about 18
On the relativistic field theory model of the deuteron II
The relativistic field theory model of the deuteron is applied to the
calculation of the cross sections of the low-energy radiative neutron-proton
capture n + p -> D + gamma and the low-energy two-proton fusion p + p -> D +
e^+ + nu_e. For the low-energy radiative neutron-proton capture n + p -> D +
gamma our result agrees well with both the experimental data and the potential
model prediction. In the case of the two-proton fusion the cross section
obtained is 2.9 times as much as that given by the potential approach. The
obtained result is discussed in connection with the solar neutrino problem.
ERRATUM: We correct the value of the cross section for pp-fusion p + p -> D +
e^+ + nu_e. We find a contribution to the astrophysical factor \delta S_pp(0) =
2.01 x 10^{-25} (1 +/- 0.30) MeV b which is obtained only due to weak and
strong low-energy interactions of the protons and the deuteron when neglecting
the Coulomb repulsion between protons in the intermediate state. Minor
misprints are corrected.Comment: 35 pages, LaTeX, plus 5 figures added as postscript files, ERRATUM: 3
pages, to appear in Nucl. Phys. A added at the en
Magnetic phase diagram of a frustrated ferrimagnetic ladder: Relation to the one-dimensional boson Hubbard model
We study the magnetic phase diagram of two coupled mixed-spin
Heisenberg chains as a function of the frustration parameter related to
diagonal exchange couplings. The analysis is performed by using spin-wave
series and exact numerical diagonalization techniques. The obtained phase
diagram--containing the Luttinger liquid phase, the plateau phase with a
magnetization per rung , and the fully polarized phase--is closely
related to the generic phase diagram of the one-dimensional boson
Hubbard model.Comment: 4 pages, 2 figure
On kaonic hydrogen. Phenomenological quantum field theoretic model revisited
We argue that due to isospin and U-spin invariance of strong low-energy
interactions the S-wave scattering lengths a^0_0 and a^1_0 of bar-KN scattering
with isospin I=0 and I = 1 satisfy the low-energy theorem a^0_0 + 3 a^1_0 = 0
valid to leading order in chiral expansion. In the model of strong low-energy
bar-KN interactions at threshold (EPJA 21,11 (2004)) we revisit the
contribution of the Sigma(1750) resonance, which does not saturate the
low-energy theorem a^0_0 + 3 a^1_0 = 0, and replace it by the baryon background
with properties of an SU(3) octet. We calculate the S-wave scattering
amplitudes of K^-N and K^-d scattering at threshold. We calculate the energy
level displacements of the ground states of kaonic hydrogen and kaonic
deuterium. The result obtained for kaonic hydrogen agrees well with recent
experimental data by the DEAR Collaboration. We analyse the cross sections for
elastic and inelastic K^-p scattering for laboratory momenta of the incident
K^- meson from the domain 70 MeV/c < p_K < 150 MeV/c. The theoretical results
agree with the available experimental data within two standard deviations.Comment: 20 pages, Latex, We have slightly corrected the contribution of the
double scattering. This changes the S-wave scattering length of K^-d
scattering by 17%, which is commensurable with the theoretical uncertaint
Terahertz Response of Acoustically-Driven Optical Phonons
The manipulation of TO-phonon polaritons and the terahertz (THz) light field
associated with them by means of an ultra-sound acoustic wave is proposed and
illustrated by calculating the TO-phonon-mediated THz response of
acoustically-pumped CuCl and TlCl crystals. We show the high-contrast
acoustically-induced change of the THz reflectivity alongside with multiple THz
Bragg replicas, which are associated with the infrared-active TO-phonon
resonance driven by the ultrasonic wave. The effect, which stems from phonon
anharmonicity, refers to an operating acoustic intensity I_ac ~ 1-100 kW/cm^2
and frequency nu_ac ~ 0.1 - 1 GHz, with possible applications in THz
spectroscopy.Comment: 10 pages, 4 figure
Impurity center in a semiconductor quantum ring in the presence of a radial electric field
The problem of an impurity electron in a quantum ring (QR) in the presence of
a radially directed strong external electric field is investigated in detail.
Both an analytical and a numerical approach to the problem are developed. The
analytical investigation focuses on the regime of a strong wire-electric field
compared to the electric field due to the impurity. An adiabatic and
quasiclassical approximation is employed. The explicit dependencies of the
binding energy of the impurity electron on the electric field strength,
parameters of the QR and position of the impurity within the QR are obtained.
Numerical calculations of the binding energy based on a finite-difference
method in two and three dimensions are performed for arbitrary strengths of the
electric field. It is shown that the binding energy of the impurity electron
exhibits a maximum as a function of the radial position of the impurity that
can be shifted arbitrarily by applying a corresponding wire-electric field. The
maximal binding energy monotonically increases with increasing electric field
strength. The inversion effect of the electric field is found to occur. An
increase of the longitudinal displacement of the impurity typically leads to a
decrease of the binding energy. Results for both low- and high-quantum rings
are derived and discussed. Suggestions for an experimentally accessible set-up
associated with the GaAs/GaAlAs QR are provided.Comment: 16 pages, 8 figure
Resonant acousto-optics in the terahertz range: TO-phonon polaritons driven by an ultrasonic wave
The resonant acousto-optic effect is studied both analytically and
numerically in the terahertz range where the transverse-optical (TO) phonons
play the role of a mediator which strongly couples the ultrasound and light
fields. A propagating acoustic wave interacts with the TO phonons via
anharmonic channels and opens band gaps in the TO-phonon polariton energy
dispersion that results in pronounced Bragg scattering and reflection of the
incoming light. The separation in frequency of different Bragg replicas, which
is at the heart of acousto-optics, allows us to study the resonant
acousto-optic effect in the most simple and efficient geometry of collinear
propagation of electromagnetic and ultrasonic waves. The acoustically induced
energy gaps, Bragg reflection spectra, and the spatial distribution of the
electric field and polarization are calculated for CuCl parameters, in a wide
range of frequencies and intensities of the pumping acoustic wave. Our results
show drastic changes in terahertz spectra of semiconductor crystals that opens
the way for efficient and accessible manipulation of their infrared properties,
by tuning the parameters of the acoustic wave.Comment: 20 pages, 14 figure
The semileptonic decays of the B_c meson
We study the semileptonic transitions B_c to \eta_c, J/\psi, D, D^*, B, B^*,
B_s, B_s^* in the framework of a relativistic constituent quark model. We use
experimental data on leptonic J/\psi decay, lattice and QCD sum rule results on
leptonic B_c decay, and on radiative \eta_c transitions to adjust the quark
model parameters. We compute all form factors of the above semileptonic
B_c-transitions and give predictions for various semileptonic B_c decay modes
including their \tau-modes when they are kinematically accessible. The
implications of heavy quark symmetry for the semileptonic decays are discussed
and are shown to be manifest in our explicit relativistic quark model
calculation. A comparison of our results with the results of other calculations
is performed.Comment: 31 pages Latex (uses epsf, revtex). Section II expanded, typos
corrected. This version will appear in Phys. Rev.
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