1,572 research outputs found
Neutrino Observatories Can Characterize Cosmic Sources and Neutrino Properties
Neutrino telescopes that measure relative fluxes of ultrahigh-energy
can give information about the location and
characteristics of sources, about neutrino mixing, and can test for neutrino
instability and for departures from CPT invariance in the neutrino sector. We
investigate consequences of neutrino mixing for the neutrino flux arriving at
Earth, and consider how terrestrial measurements can characterize distant
sources. We contrast mixtures that arise from neutrino oscillations with those
signaling neutrino decays. We stress the importance of measuring fluxes in neutrino observatories.Comment: 9 RevTeX pages, 4 figure
Test of renormalization predictions for universal finite-size scaling functions
We calculate universal finite-size scaling functions for systems with an
n-component order parameter and algebraically decaying interactions. Just as
previously has been found for short-range interactions, this leads to a
singular epsilon-expansion, where epsilon is the distance to the upper critical
dimension. Subsequently, we check the results by numerical simulations of spin
models in the same universality class. Our systems offer the essential
advantage that epsilon can be varied continuously, allowing an accurate
examination of the region where epsilon is small. The numerical calculations
turn out to be in striking disagreement with the predicted singularity.Comment: 6 pages, including 3 EPS figures. To appear in Phys. Rev. E. Also
available as PDF file at
http://www.cond-mat.physik.uni-mainz.de/~luijten/erikpubs.htm
Critical structure factor in Ising systems
We perform a large-scale Monte Carlo simulation of the three-dimensional
Ising model on simple cubic lattices of size L^3 with L=128 and 256. We
determine the corresponding structure factor (Fourier transform of the
two-point function) and compare it with several approximations and with
experimental results. We also compute the turbidity as a function of the
momentum of the incoming radiation, focusing in particular on the deviations
from the Ornstein-Zernicke expression of Puglielli and Ford.Comment: 16 page
Exact multilocal renormalization on the effective action : application to the random sine Gordon model statics and non-equilibrium dynamics
We extend the exact multilocal renormalization group (RG) method to study the
flow of the effective action functional. This important physical quantity
satisfies an exact RG equation which is then expanded in multilocal components.
Integrating the nonlocal parts yields a closed exact RG equation for the local
part, to a given order in the local part. The method is illustrated on the O(N)
model by straightforwardly recovering the exponent and scaling
functions. Then it is applied to study the glass phase of the Cardy-Ostlund,
random phase sine Gordon model near the glass transition temperature. The
static correlations and equilibrium dynamical exponent are recovered and
several new results are obtained. The equilibrium two-point scaling functions
are obtained. The nonequilibrium, finite momentum, two-time response and
correlations are computed. They are shown to exhibit scaling forms,
characterized by novel exponents , as well as
universal scaling functions that we compute. The fluctuation dissipation ratio
is found to be non trivial and of the form . Analogies and
differences with pure critical models are discussed.Comment: 33 pages, RevTe
Condensation of Hard Spheres Under Gravity: Exact Results in One Dimension
We present exact results for the density profile of the one dimensional array
of N hard spheres of diameter D and mass m under gravity g. For a strictly one
dimensional system, the liquid-solid transition occurs at zero temperature,
because the close-pakced density, , is one. However, if we relax this
condition slightly such that , we find a series of critical
temperatures T_c^i=mgD(N+1-i)/\mu_o with \mu_o=const, at which the i-th
particle undergoes the liquid-solid transition. The functional form of the
onset temperature, T_c^1=mgDN/\mu_o, is consistent with the previous result
[Physica A 271, 192 (1999)] obtained by the Enskog equation. We also show that
the increase in the center of mass is linear in T before the transition, but it
becomes quadratic in T after the transition because of the formation of solid
near the bottom
Real space renormalization group approach to the 2d antiferromagnetic Heisenberg model
The low energy behaviour of the 2d antiferromagnetic Heisenberg model is
studied in the sector with total spins by means of a renormalization
group procedure, which generates a recursion formula for the interaction matrix
of 4 neighbouring " clusters" of size ,
from the corresponding quantities . Conservation
of total spin is implemented explicitly and plays an important role. It is
shown, how the ground state energies , approach each
other for increasing , i.e. system size. The most relevant couplings in the
interaction matrices are generated by the transitions
between the ground states
() on an -cluster of size , mediated
by the staggered spin operator Comment: 18 pages, 8 figures, RevTe
Two-particle pairing and phase separation in a two-dimensional Bose-gas with one or two sorts of bosons
We present a phase diagram for a dilute two-dimensional Bose-gas on a
lattice. For one sort of boson we consider a realistic case of the van der
Waals interaction between particles with a strong hard-core repulsion and a
van der Waals attractive tail . For , being a hopping
amplitude, the phase diagram of the system contains regions of the usual
one-particle Bose-Einstein condensation (BEC). However for we have total
phase separation on a Mott-Hubbard Bose solid and a dilute Bose gas. For two
sorts of structureless bosons described by the two band Hubbard model an s-wave
pairing of the two bosons of different sort is possible.
The results we obtained should be important for different Bose systems,
including submonolayers of He, excitons in semiconductors, Schwinger bosons
in magnetic systems and holons in HTSC. In the HTSC case a possibility of
two-holon pairing in the slave-bosons theories of superconductivity can restore
a required charge of a Cooper pair.Comment: 10 pages, 2 figure
Soft lepton-flavor violation in a multi-Higgs-doublet seesaw model
We consider the Standard Model with an arbitrary number n_H of Higgs doublets
and enlarge the lepton sector by adding to each lepton family \ell a
right-handed neutrino singlet \nu_{\ell R}. We assume that all Yukawa-coupling
matrices are diagonal, but the Majorana mass matrix M_R of the right-handed
neutrino singlets is an arbitrary symmetric matrix, thereby introducing an
explicit but soft violation of all lepton numbers. We investigate
lepton-flavor-violating processes within this model. We pay particular
attention to the large-m_R behavior of the amplitudes for these processes,
where m_R is the order of magnitude of the matrix elements of M_R. While the
amplitudes for processes like tau^- --> mu^- gamma and Z --> tau^+ mu^- drop as
1/m_R^2 for arbitrary n_H, processes like tau^- --> mu^- e^+ e^- and mu^- -->
e^- e^+ e^- obey this power law only for n_H = 1. For n_H \geq 2, on the
contrary, those amplitudes do not fall off when m_R increases, rather they
converge towards constants. This non-decoupling of the right-handed scale
occurs because of the sub-process ell^- --> ell'^- {S_b^0}^*, where S_b^0 is a
neutral scalar which subsequently decays to e^+ e^-. That sub-process has a
contribution from charged-scalar exchange which, for n_H \geq 2, does not
decrease when m_R tends to infinity. We also perform a general study of the
non-decoupling and argue that, after performing the limit m_R --> \infty and
removing the \nu_R from the Lagrangian, our model becomes a multi-Higgs-doublet
Standard Model with suppressed flavor-changing Yukawa couplings. Finally, we
show that, with the usual assumptions about the mass scales in the seesaw
mechanism, the branching ratios of all lepton-flavor-changing processes are
several orders of magnitude smaller than present experimental limits.Comment: 46 pages, 2 figures, Revte
Dual Vortex Theory of Strongly Interacting Electrons: Non-Fermi Liquid to the (Hard) Core
As discovered in the quantum Hall effect, a very effective way for
strongly-repulsive electrons to minimize their potential energy is to aquire
non-zero relative angular momentum. We pursue this mechanism for interacting
two-dimensional electrons in zero magnetic field, by employing a representation
of the electrons as composite bosons interacting with a Chern-Simons gauge
field. This enables us to construct a dual description in which the fundamental
constituents are vortices in the auxiliary boson fields. The resulting
formalism embraces a cornucopia of possible phases. Remarkably,
superconductivity is a generic feature, while the Fermi liquid is not --
prompting us to conjecture that such a state may not be possible when the
interactions are sufficiently strong. Many aspects of our earlier discussions
of the nodal liquid and spin-charge separation find surprising incarnations in
this new framework.Comment: Modified dicussion of the hard-core model, correcting several
mistake
Velocity-force characteristics of an interface driven through a periodic potential
We study the creep dynamics of a two-dimensional interface driven through a
periodic potential using dynamical renormalization group methods. We find that
the nature of weak-drive transport depends qualitatively on whether the
temperature is above or below the equilibrium roughening transition
temperature . Above , the velocity-force characteristics is Ohmic,
with linear mobility exhibiting a jump discontinuity across the transition. For
, the transport is highly nonlinear, exhibiting an interesting
crossover in temperature and weak external force . For intermediate drive,
, we find near a power-law velocity-force characteristics
, with , and well-below ,
, with . In the limit
of vanishing drive () the velocity-force characteristics crosses over
to , and is controlled by soliton nucleation.Comment: 18 pages, submitted to Phys. Rev.
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