25,250 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
Non-dopplerian cosmological redshift parameters in a model of graviton-dusty universe
Possible effects are considered which would be caused by a hypothetical
superstrong interaction of photons or massive bodies with single gravitons of
the graviton background. If full cosmological redshift magnitudes are caused by
the interaction, then the luminosity distance in a flat non-expanding universe
as a function of redshift is very similar to the specific function which fits
supernova cosmology data by Riess et al. From another side, in this case every
massive body, slowly moving relatively to the background, would experience a
constant acceleration, proportional to the Hubble constant, of the same order
as a small additional acceleration of Pioneer 10, 11.Comment: 5 pages. It was presented: at SIGRAV'2000 Congress, Italy (this
version); in Proc. of the Int. Symp. "FFP 4" (9-13 Dec 2000, Hyderabad,
India), Sidharth& Altaisky, Eds., Kluwer Academic/Plenum, 2001;in Proc. of
the 4th Edoardo Amaldi Conference on GW (Perth, W. Australia, 8-13 July 2001
Phase diagram of the alternating-spin Heisenberg chain with extra isotropic three-body exchange interactions
For the time being isotropic three-body exchange interactions are scarcely
explored and mostly used as a tool for constructing various exactly solvable
one-dimensional models, although, generally speaking, such competing terms in
generic Heisenberg spin systems can be expected to support specific quantum
effects and phases. The Heisenberg chain constructed from alternating S=1 and
sigma=1/2 site spins defines a realistic prototype model admitting extra
three-body exchange terms. Based on numerical density-matrix renormalization
group (DMRG) and exact diagonalization (ED) calculations, we demonstrate that
the additional isotropic three-body terms stabilize a variety of
partially-polarized states as well as two specific non-magnetic states
including a critical spin-liquid phase controlled by two Gaussinal conformal
theories as well as a critical nematic-like phase characterized by dominant
quadrupolar S-spin fluctuations. Most of the established effects are related to
some specific features of the three-body interaction such as the promotion of
local collinear spin configurations and the enhanced tendency towards
nearest-neighbor clustering of the spins. It may be expected that most of the
predicted effects of the isotropic three-body interaction persist in higher
space dimensions.Comment: 13 pages, 17 figures, submitte
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
On kaonic hydrogen. Quantum field theoretic and relativistic covariant approach
We study kaonic hydrogen, the bound K^-p state A_(Kp). Within a quantum field
theoretic and relativistic covariant approach we derive the energy level
displacement of the ground state of kaonic hydrogen in terms of the amplitude
of K^-p scattering for arbitrary relative momenta. The amplitude of low-energy
K^-p scattering near threshold is defined by the contributions of three
resonances Lambda(1405), Lambda(1800) and Sigma^0(1750) and a smooth elastic
background. The amplitudes of inelastic channels of low-energy K^-p scattering
fit experimental data on near threshold behaviour of the cross sections and the
experimental data by the DEAR Collaboration. We use the soft-pion technique
(leading order in Chiral Perturbation Theory) for the calculation of the
partial width of the radiative decay of pionic hydrogen A_(pi p) -> n + gamma
and the Panofsky ratio. The theoretical prediction for the Panofsky ratio
agrees well with experimental data. We apply the soft-kaon technique (leading
order in Chiral Perturbation Theory) to the calculation of the partial widths
of radiative decays of kaonic hydrogen A_(Kp) -> Lambda^0 + gamma and A_(Kp) ->
Sigma^0 + gamma. We show that the contribution of these decays to the width of
the energy level of the ground state of kaonic hydrogen is less than 1%.Comment: 33 pages, 1 figure, latex, References are adde
Deformations of generalized calibrations and compact non-Kahler manifolds with vanishing first Chern class
We investigate the deformation theory of a class of generalized calibrations
in Riemannian manifolds for which the tangent bundle has reduced structure
group U(n), SU(n), G_2 and Spin(7). For this we use the property of the
associated calibration form to be parallel with respect to a metric connection
which may have non-vanishing torsion. In all these cases, we find that if there
is a moduli space, then it is finite dimensional.
We present various examples of generalized calibrations that include almost
hermitian manifolds with structure group U(n) or SU(n), nearly parallel G_2
manifolds and group manifolds. We find that some Hopf fibrations are
deformation families of generalized calibrations. In addition, we give
sufficient conditions for a hermitian manifold (M,g,J) to admit Chern and
Bismut connections with holonomy contained in SU(n). In particular we show that
any connected sum of copies of admits a hermitian
structure for which the restricted holonomy of a Bismut connection is contained
in SU(3).Comment: 43 pages, Latex, typos corrected, reference added in section
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
Higgs masses of the general 2HDM in the Minkowski-space formalism
We study the masses of the Higgs bosons in the most general two-Higgs-doublet
model in a basis-independent approach. We adapt the recently developed
Minkowski-space formalism to this problem and calculate traces of any power of
the mass-matrix in a compact and reparametrization-invariant form. Our results
can be used to gain insight into the dynamics of the scalar sector of the
general 2HDM.Comment: 14 pages, no figures; v2: reference added, misprints correcte
Conformal and Superconformal Mechanics Revisited
We find, at the Lagrangian off-shell level, the explicit equivalence
transformation which relates the conformal mechanics of De Alfaro, Fubini and
Furlan to the conformal mechanics describing the radial motion of the charged
massive particle in the Bertotti-Robinson AdS background. Thus we
demonstrate the classical equivalence of these two systems which are usually
regarded as essentially different ``old'' and ``new'' conformal mechanics
models. We also construct a similar transformation for N=2,
superconformal mechanics in N=2 superfield formulation. Performing this
transformation in the action of the N=2 superconformal mechanics, we find an
off-shell superfield action of N=2 superextension of Bertotti-Robinson
particle. Such an action has not been given before. We show its on-shell
equivalence to the AdS superparticle action derived from the spontaneous
partial breaking of superconformal symmetry treated as the N=2
AdS supersymmetry.Comment: LaTeX, 15 page
On The Violation Of Marshall-Peierls Sign Rule In The Frustrated Heisenberg Antiferromagnet
We present a number of arguments in favor of the suggestion that the
Marshall-Peierls sign rule survives the frustration in the square-lattice
Heisenberg antiferromagnet with frustrating next-nearest-neighbor (diagonal)
bonds ( model) for relatively large values of the parameter
. Both the spin-wave analysis and the exact-diagonalization data
concerning the weight of Marshall states support the above suggestion.Comment: 8 pages, LaTex, 2 figurs on reques
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