263,112 research outputs found
Chiral expansion of the decay width
A chiral field theory of mesons has been applied to study the contribution of
the current quark masses to the decay width at
the next leading order. enhancement has been predicted and there is no
new parameter.Comment: 9 page
A Rate-Splitting Based Bound-Approaching Transmission Scheme for the Two-User Symmetric Gaussian Interference Channel with Common Messages
This paper is concerned with a rate-splitting based transmission strategy for the two-user symmetric Gaussian interference channel that contains common messages only. Each transmitter encodes its common message into multiple layers by multiple codebooks that drawn from one separate code book, and transmits the superposition of the messages corresponding to these layers; each receiver decodes the messages from all layers of the two users successively. Two schemes are proposed for decoding order and optimal power allocation among layers respectively. With the proposed decoding order scheme, the sum-rate can be increased by rate-splitting, especially at the optimal number of rate-splitting, using average power allocation in moderate and weak interference regime. With the two proposed schemes at the receiver and the transmitter respectively, the sum-rate achieves the inner bound of HK without time-sharing. Numerical results show that the proposed optimal power allocation scheme with the proposed decoding order can achieve significant improvement of the performance over equal power allocation, and achieve the sum-rate within two bits per channel use (bits/channel use) of the sum capacity
Asymptotically Universal Crossover in Perturbation Theory with a Field Cutoff
We discuss the crossover between the small and large field cutoff (denoted
x_{max}) limits of the perturbative coefficients for a simple integral and the
anharmonic oscillator. We show that in the limit where the order k of the
perturbative coefficient a_k(x_{max}) becomes large and for x_{max} in the
crossover region, a_k(x_{max}) is proportional to the integral from -infinity
to x_{max} of e^{-A(x-x_0(k))^2}dx. The constant A and the function x_0(k) are
determined empirically and compared with exact (for the integral) and
approximate (for the anharmonic oscillator) calculations. We discuss how this
approach could be relevant for the question of interpolation between
renormalization group fixed points.Comment: 15 pages, 11 figs., improved and expanded version of hep-th/050304
Particle Spectrum of the Supersymmetric Standard Model from the Massless Excitations of a Four Dimensional Superstring
A superstring action is quantised with Neveu Schwarz(NS) and Ramond(R)
boundary conditions. The zero mass states of the NS sector are classified as
the vector gluons, W-mesons, -mesons and scalars containing Higgs. The
fifteen zero mass fermions are obtained from the Ramond sector. A space time
supersymmetric Hamiltonian of the Standard Model is presented without any
conventional SUSY particles
Correlations of chaotic eigenfunctions: a semiclassical analysis
We derive a semiclassical expression for an energy smoothed autocorrelation
function defined on a group of eigenstates of the Schr\"odinger equation. The
system we considered is an energy-conserved Hamiltonian system possessing
time-invariant symmetry. The energy smoothed autocorrelation function is
expressed as a sum of three terms. The first one is analogous to Berry's
conjecture, which is a Bessel function of the zeroth order. The second and the
third terms are trace formulae made from special trajectories. The second term
is found to be direction dependent in the case of spacing averaging, which
agrees qualitatively with previous numerical observations in high-lying
eigenstates of a chaotic billiard.Comment: Revtex, 13 pages, 1 postscript figur
Nonperturbative signatures in pair production for general elliptic polarization fields
The momentum signatures in nonperturbative multiphoton pair production for
general elliptic polarization electric fields are investigated by employing the
real-time Dirac-Heisenberg-Wigner formalism. For a linearly polarized electric
field we find that the positions of the nodes in momenta spectra of created
pairs depend only on the electric field frequency. The polarization of external
fields could not only change the node structures or even make the nodes
disappear but also change the thresholds of pair production. The momentum
signatures associated to the node positions in which the even-number-photon
pair creation process is forbid could be used to distinguish the orbital
angular momentum of created pairs on the momenta spectra. These distinguishable
momentum signatures could be relevant for providing the output information of
created particles and also the input information of ultrashort laser pulses.Comment: 8 pages, 4 figures, submitted to Europhysics Letter
- …