533 research outputs found
Quantum Hall effect anomaly and collective modes in the magnetic-field-induced spin-density-wave phases of quasi-one-dimensional conductors
We study the collective modes in the magnetic-field-induced spin-density-wave
(FISDW) phases experimentally observed in organic conductors of the Bechgaard
salts family. In phases that exhibit a sign reversal of the quantum Hall effect
(Ribault anomaly), the coexistence of two spin-density waves gives rise to
additional collective modes besides the Goldstone modes due to spontaneous
translation and rotation symmetry breaking. These modes strongly affect the
charge and spin response functions. We discuss some experimental consequences
for the Bechgaard salts.Comment: Final version (LaTex, 8 pages, no figure), to be published in
Europhys. Let
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
Next-to-leading order QCD corrections to W+W- production via vector-boson fusion
Vector-boson fusion processes constitute an important class of reactions at
hadron colliders, both for signals and backgrounds of new physics in the
electroweak interactions.
We consider what is commonly referred to as W+W- production via vector-boson
fusion (with subsequent leptonic decay of the Ws), or, more precisely, e+ nu_e
mu- nubar_mu + 2 jets production in proton-proton scattering, with all resonant
and non-resonant Feynman diagrams and spin correlations of the final-state
leptons included, in the phase-space regions which are dominated by t-channel
electroweak-boson exchange.
We compute the next-to-leading order QCD corrections to this process, at
order alpha^6 alpha_s.
The QCD corrections are modest, changing total cross sections by less than
10%. Remaining scale uncertainties are below 2%. A fully-flexible
next-to-leading order partonic Monte Carlo program allows to demonstrate these
features for cross sections within typical vector-boson-fusion acceptance cuts.
Modest corrections are also found for distributions.Comment: 29 pages, 14 figure
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
Electroweak Precision Constraints on the Littlest Higgs Model with T Parity
We compute the leading corrections to the properties of W and Z bosons
induced at the one-loop level in the SU(5)/SO(5) Littlest Higgs model with T
parity, and perform a global fit to precision electroweak data to determine the
constraints on the model parameters. We find that a large part of the model
parameter space is consistent with data. Values of the symmetry breaking scale
as low as 500 GeV are allowed, indicating that no significant fine tuning in
the Higgs potential is required. We identify a region within the allowed
parameter space in which the lightest T-odd particle, the partner of the
hypercharge gauge boson, has the correct relic abundance to play the role of
dark matter. In addition, we find that a consistent fit to data can be obtained
for large values of the Higgs mass, up to 800 GeV, due to the possibility of a
partial cancellation between the contributions to the T parameter from Higgs
loops and new physics.Comment: 23 pages, 9 figures. Minor correction
Open-closed duality and Double Scaling
Nonperturbative terms in the free energy of Chern-Simons gauge theory play a
key role in its duality to the closed topological string. We show that these
terms are reproduced by performing a double scaling limit near the point where
the perturbation expansion diverges. This leads to a derivation of closed
string theory from this large-N gauge theory along the lines of noncritical
string theories. We comment on the possible relevance of this observation to
the derivation of superpotentials of asymptotically free gauge theories and its
relation to infrared renormalons.Comment: 10 pages, LaTe
Generating Function for Particle-Number Probability Distribution in Directed Percolation
We derive a generic expression for the generating function (GF) of the
particle-number probability distribution (PNPD) for a simple reaction diffusion
model that belongs to the directed percolation universality class. Starting
with a single particle on a lattice, we show that the GF of the PNPD can be
written as an infinite series of cumulants taken at zero momentum. This series
can be summed up into a complete form at the level of a mean-field
approximation. Using the renormalization group techniques, we determine
logarithmic corrections for the GF at the upper critical dimension. We also
find the critical scaling form for the PNPD and check its universality
numerically in one dimension. The critical scaling function is found to be
universal up to two non-universal metric factors.Comment: (v1,2) 8 pages, 5 figures; one-loop calculation corrected in response
to criticism received from Hans-Karl Janssen, (v3) content as publishe
An Effect of Corrections on Racetrack Inflation
We study the effects of corrections to the K\"ahler potential on
volume stabilisation and racetrack inflation. In a region where classical
supergravity analysis is justified, stringy corrections can nevertheless be
relevant for correctly analyzing moduli stabilisation and the onset of
inflation.Comment: 13 pages, 4 figures. Typos corrected, references added, this version
to appear in JHE
Neutralino, axion and axino cold dark matter in minimal, hypercharged and gaugino AMSB
Supersymmetric models based on anomaly-mediated SUSY breaking (AMSB)
generally give rise to a neutral wino as a WIMP cold dark matter (CDM)
candidate, whose thermal abundance is well below measured values. Here, we
investigate four scenarios to reconcile AMSB dark matter with the measured
abundance: 1. non-thermal wino production due to decays of scalar fields ({\it
e.g} moduli), 2. non-thermal wino production due to decays of gravitinos, 3.
non-thermal wino production due to heavy axino decays, and 4. the case of an
axino LSP, where the bulk of CDM is made up of axions and thermally produced
axinos. In cases 1 and 2, we expect wino CDM to constitute the entire measured
DM abundance, and we investigate wino-like WIMP direct and indirect detection
rates. Wino direct detection rates can be large, and more importantly, are
bounded from below, so that ton-scale noble liquid detectors should access all
of parameter space for m_{\tz_1}\alt 500 GeV. Indirect wino detection rates via
neutrino telescopes and space-based cosmic ray detectors can also be large. In
case 3, the DM would consist of an axion plus wino admixture, whose exact
proportions are very model dependent. In this case, it is possible that both an
axion and a wino-like WIMP could be detected experimentally. In case 4., we
calculate the re-heat temperature of the universe after inflation. In this
case, no direct or indirect WIMP signals should be seen, although direct
detection of relic axions may be possible. For each DM scenario, we show
results for the minimal AMSB model, as well as for the hypercharged and gaugino
AMSB models.Comment: 29 pages including 13 figure
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