3,209 research outputs found
Spectra of magnetic fluctuations and relativistic particles produced by a nonresonant wave instability in supernova remnant shocks
We model strong forward shocks in young supernova remnants with efficient
particle acceleration where a nonresonant instability driven by the cosmic ray
current amplifies magnetic turbulence in the shock precursor. Particle
injection, magnetic field amplification (MFA) and the nonlinear feedback of
particles and fields on the bulk flow are derived consistently. The shock
structure depends critically on the efficiency of turbulence cascading. If
cascading is suppressed, MFA is strong, the shock precursor is stratified, and
the turbulence spectrum contains several discrete peaks. These peaks, as well
as the amount of MFA, should influence synchrotron X-rays, allowing
observational tests of cascading and other assumptions intrinsic to the
nonlinear model of nonresonant wave growth.Comment: 3 figures, 5 pages. Accepted for publication in ApJ
Nonlinear equations for p-adic open, closed, and open-closed strings
We investigate the structure of solutions of boundary value problems for a
one-dimensional nonlinear system of pseudodifferential equations describing the
dynamics (rolling) of p-adic open, closed, and open-closed strings for a scalar
tachyon field using the method of successive approximations. For an open-closed
string, we prove that the method converges for odd values of p of the form
p=4n+1 under the condition that the solution for the closed string is known.
For p=2, we discuss the questions of the existence and the nonexistence of
solutions of boundary value problems and indicate the possibility of
discontinuous solutions appearing.Comment: 16 pages, 3 figure
Spin excitations and thermodynamics of the t-J model on the honeycomb lattice
We present a spin-rotation-invariant Green-function theory for the dynamic
spin susceptibility in the spin-1/2 antiferromagnetic t-J Heisenberg model on
the honeycomb lattice. Employing a generalized mean-field approximation for
arbitrary temperatures and hole dopings, the electronic spectrum of
excitations, the spin-excitation spectrum and thermodynamic quantities
(two-spin correlation functions, staggered magnetization, magnetic
susceptibility, correlation length) are calculated by solving a coupled system
of self-consistency equations for the correlation functions. The temperature
and doping dependence of the magnetic (uniform static) susceptibility is
ascribed to antiferromagnetic short-range order. Our results on the doping
dependencies of the magnetization and susceptibility are analyzed in comparison
with previous results for the t_J model on the square lattice.Comment: 9 pages, 7 figures, submitted to European Physical Journal B. arXiv
admin note: text overlap with arXiv:1703.0839
Superconductivity of strongly correlated electrons on the honeycomb lattice
A microscopic theory of the electronic spectrum and of superconductivity
within the t-J model on the honeycomb lattice is developed. We derive the
equations for the normal and anomalous Green functions in terms of the Hubbard
operators by applying the projection technique. Superconducting pairing of d +
id'-type mediated by the antiferromagnetic exchange is found. The
superconducting Tc as a function of hole doping exhibits a two-peak structure
related to the van Hove singularities of the density of states for the two-band
t-J model. At half-filling and for large enough values of the exchange
coupling, gapless superconductivity may occur. For small doping the coexistence
of antiferromagnetic order and superconductivity is suggested. It is shown that
the s-wave pairing is prohibited, since it violates the constraint of
no-double-occupancy.Comment: 10 pages, 3 figures, to be published in Eur. Phys. J.
Dynamic spin susceptibility of superconducting cuprates: A microscopic theory of the magnetic resonance mode
A microscopic theory of the dynamic spin susceptibility (DSS) in the
superconducting state within the t-J model is presented. It is based on an
exact representation for the DSS obtained by applying the Mori-type projection
technique for the relaxation function in terms of Hubbard operators. The static
spin susceptibility is evaluated by a sum-rule-conserving generalized
mean-field approximation, while the self-energy is calculated in the
mode-coupling approximation. The spectrum of spin excitations is studied in the
underdoped and optimally doped regions. The DSS reveals a resonance mode (RM)
at the antiferromagnetic wave vector Q = \pi(1,1) at low temperatures due to a
strong suppression of the damping of spin excitations. This is explained by an
involvement of spin excitations in the decay process besides the particle-hole
continuum usually considered in random-phase-type approximations. The spin gap
in the spin-excitation spectrum at Q plays a dominant role in limiting the
decay in comparison with the superconducting gap which results in the
observation of the RM even above in the underdoped region. A good
agreement with inelastic neutron-scattering experiments on the RM in YBCO
compounds is found.Comment: 15 pages, 20 figures, references adde
Electroproduction of tensor mesons in QCD
Due to multiple possible polarizations hard exclusive production of tensor
mesons by virtual photons or in heavy meson decays offers interesting
possibilities to study the helicity structure of the underlying short-distance
process. Motivated by the first measurement of the transition form factor
at large momentum transfers by the BELLE
collaboration we present an improved QCD analysis of this reaction in the
framework of collinear factorization including contributions of twist-three
quark-antiquark-gluon operators and an estimate of soft end-point corrections
using light-cone sum rules. The results appear to be in a very good agreement
with the data, in particular the predicted scaling behavior is reproduced in
all cases.Comment: 27 pages, 5 figure
Noncommutative magnetic moment of charged particles
It has been argued, that in noncommutative field theories sizes of physical
objects cannot be taken smaller than an elementary length related to
noncommutativity parameters. By gauge-covariantly extending field equations of
noncommutative U(1)_*-theory to the presence of external sources, we find
electric and magnetic fields produces by an extended charge. We find that such
a charge, apart from being an ordinary electric monopole, is also a magnetic
dipole. By writing off the existing experimental clearance in the value of the
lepton magnetic moments for the present effect, we get the bound on
noncommutativity at the level of 10^4 TeV.Comment: 9 pages, revtex; v2: replaced to match the published versio
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