433 research outputs found
The scalars from the topcolor scenario and the spin correlations of the top pair production at the LHC
The topcolor scenario predicts the existences of some new scalars. In this
paper, we consider the contributions of these new particles to the observables,
which are related to the top quark pair () production at the LHC. It
is found that these new particles can generate significant corrections to the
production cross section and the spin correlations.Comment: 23 pages, 4 figures; discussions and references added; agrees with
published versio
Kinetically driven glassy transition in an exactly solvable toy model with reversible mode coupling mechanism and trivial statics
We propose a toy model with reversible mode coupling mechanism and with
trivial Hamiltonian (and hence trivial statics). The model can be analyzed
exactly without relying upon uncontrolled approximation such as the
factorization approximation employed in the current MCT. We show that the model
exhibits a kinetically driven transition from an ergodic phase to nonergodic
phase. The nonergodic state is the nonequilibrium stationary solution of the
Fokker-Planck equation for the distribution function of the modelComment: 10 pages, 1 figure, contribution to the Proceedings of the Barcelona
Workshop 'Glassy Behavior of Kinetically Constrained Models'. To appear in J.
Phys. Condens. Matte
Critical Exponents of the Three Dimensional Random Field Ising Model
The phase transition of the three--dimensional random field Ising model with
a discrete () field distribution is investigated by extensive Monte
Carlo simulations. Values of the critical exponents for the correlation length,
specific heat, susceptibility, disconnected susceptibility and magnetization
are determined simultaneously via finite size scaling. While the exponents for
the magnetization and disconnected susceptibility are consistent with a first
order transition, the specific heat appears to saturate indicating no latent
heat. Sample to sample fluctuations of the susceptibilty are consistent with
the droplet picture for the transition.Comment: Revtex, 10 pages + 4 figures included as Latex files and 1 in
Postscrip
Two-Scale Annihilation
The kinetics of single-species annihilation, , is investigated in
which each particle has a fixed velocity which may be either with equal
probability, and a finite diffusivity. In one dimension, the interplay between
convection and diffusion leads to a decay of the density which is proportional
to . At long times, the reactants organize into domains of right- and
left-moving particles, with the typical distance between particles in a single
domain growing as , and the distance between domains growing as .
The probability that an arbitrary particle reacts with its
neighbor is found to decay as for same-velocity pairs and as
for pairs. These kinetic and spatial exponents and their
interrelations are obtained by scaling arguments. Our predictions are in
excellent agreement with numerical simulations.Comment: revtex, 5 pages, 5 figures, also available from
http://arnold.uchicago.edu/~eb
Effective Potential for Uniform Magnetic Fields through Pauli Interaction
We have calculated the explicit form of the real and imaginary parts of the
effective potential for uniform magnetic fields which interact with spin-1/2
fermions through the Pauli interaction. It is found that the non-vanishing
imaginary part develops for a magnetic field stronger than a critical field,
whose strength is the ratio of the fermion mass to its magnetic moment. This
implies the instability of the uniform magnetic field beyond the critical field
strength to produce fermion pairs with the production rate density
in the
presence of Pauli interaction.Comment: 9 pages with 1 figur
Octet baryon electromagnetic form factors in nuclear medium
We study the octet baryon electromagnetic form factors in nuclear matter
using the covariant spectator quark model extended to the nuclear matter
regime. The parameters of the model in vacuum are fixed by the study of the
octet baryon electromagnetic form factors. In nuclear matter the changes in
hadron properties are calculated by including the relevant hadron masses and
the modification of the pion-baryon coupling constants calculated in the
quark-meson coupling model. In nuclear matter the magnetic form factors of the
octet baryons are enhanced in the low region, while the electric form
factors show a more rapid variation with . The results are compared with
the modification of the bound proton electromagnetic form factors observed at
Jefferson Lab. In addition, the corresponding changes for the bound neutron are
predicted.Comment: Version accepted for publication in J.Phys. G. Few changes. 40 pages,
14 figures and 8 table
Flux quantization and superfluid weight in doped antiferromagnets
Doped antiferromagnets, described by a t-t'-J model and a suitable 1/N
expansion, exhibit a metallic phase-modulated antiferromagnetic ground state
close to half-filling. Here we demonstrate that the energy of latter state is
an even periodic function of the external magnetic flux threading the square
lattice in an Aharonov-Bohm geometry. The period is equal to the flux quantum
entering the Peierls phase factor of the hopping
matrix elements. Thus flux quantization and a concomitant finite value of
superfluid weight D_s occur along with metallic antiferromagnetism. We argue
that in the context of the present effective model, whereby carriers are
treated as hard-core bosons, the charge q in the associated flux quantum might
be set equal to 2e. Finally, the superconducting transition temperature T_c is
related to D_s linearly, in accordance to the generic Kosterlitz-Thouless type
of transition in a two-dimensional system, signaling the coherence of the phase
fluctuations of the condensate. The calculated dependence of T_c on hole
concentration is qualitatively similar to that observed in the high-temperature
superconducting cuprates.Comment: 5 pages, 2 figures, to be published in J. Phys. Condens. Matte
Picosecond time-resolved, polarized fluorescence decay of phycobilisomes and constituent biliproteins isolated from Mastigocladus laminosus
Langevin dynamics of the Lebowitz-Percus model
We revisit the hard-spheres lattice gas model in the spherical approximation
proposed by Lebowitz and Percus (J. L. Lebowitz, J. K. Percus, Phys. Rev.{\
144} (1966) 251). Although no disorder is present in the model, we find that
the short-range dynamical restrictions in the model induce glassy behavior. We
examine the off-equilibrium Langevin dynamics of this model and study the
relaxation of the density as well as the correlation, response and overlap
two-time functions. We find that the relaxation proceeds in two steps as well
as absence of anomaly in the response function. By studying the violation of
the fluctuation-dissipation ratio we conclude that the glassy scenario of this
model corresponds to the dynamics of domain growth in phase ordering kinetics.Comment: 21 pages, RevTeX, 14 PS figure
Are solar neutrino oscillations robust?
The robustness of the large mixing angle (LMA) oscillation (OSC)
interpretation of the solar neutrino data is considered in a more general
framework where non-standard neutrino interactions (NSI) are present. Such
interactions may be regarded as a generic feature of models of neutrino mass.
The 766.3 ton-yr data sample of the KamLAND collaboration are included in the
analysis, paying attention to the background from the reaction ^13C(\alpha,n)
^16O. Similarly, the latest solar neutrino fluxes from the SNO collaboration
are included. In addition to the solution which holds in the absence of NSI
(LMA-I) there is a 'dark-side' solution (LMA-D) with sin^2 theta_Sol = 0.70,
essentially degenerate with the former, and another light-side solution (LMA-0)
allowed only at 97% CL. More precise KamLAND reactor measurements will not
resolve the ambiguity in the determination of the solar neutrino mixing angle
theta_Sol, as they are expected to constrain mainly Delta m^2. We comment on
the complementary role of atmospheric, laboratory (e.g. CHARM) and future solar
neutrino experiments in lifting the degeneracy between the LMA-I and LMA-D
solutions. In particular, we show how the LMA-D solution induced by the
simplest NSI between neutrinos and down-type-quarks-only is in conflict with
the combination of current atmospheric data and data of the CHARM experiment.
We also mention that establishing the issue of robustness of the oscillation
picture in the most general case will require further experiments, such as
those involving low energy solar neutrinos.Comment: 13 pages, 6 figures; Final version to appear in JHE
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