1,283 research outputs found
Shock waves in two-dimensional granular flow: effects of rough walls and polydispersity
We have studied the two-dimensional flow of balls in a small angle funnel,
when either the side walls are rough or the balls are polydisperse. As in
earlier work on monodisperse flows in smooth funnels, we observe the formation
of kinematic shock waves/density waves. We find that for rough walls the flows
are more disordered than for smooth walls and that shock waves generally
propagate more slowly. For rough wall funnel flow, we show that the shock
velocity and frequency obey simple scaling laws. These scaling laws are
consistent with those found for smooth wall flow, but here they are cleaner
since there are fewer packing-site effects and we study a wider range of
parameters. For pipe flow (parallel side walls), rough walls support many shock
waves, while smooth walls exhibit fewer or no shock waves. For funnel flows of
balls with varying sizes, we find that flows with weak polydispersity behave
qualitatively similar to monodisperse flows. For strong polydispersity, scaling
breaks down and the shock waves consist of extended areas where the funnel is
blocked completely.Comment: 11 pages, 15 figures; accepted for PR
Topcolor-Assisted Supersymmetry
It has been known that the supersymmetric flavor changing neutral current
problem can be avoided if the squarks take the following mass pattern, namely
the first two generations with the same chirality are degenerate with masses
around the weak scale, while the third generation is very heavy. We realize
this scenario through the supersymmetric extension of a topcolor model with
gauge mediated supersymmetry breaking.Comment: 12 pages, latex, no figure
Probing Heavy Higgs Boson Models with a TeV Linear Collider
The last years have seen a great development in our understanding of particle
physics at the weak scale. Precision electroweak observables have played a key
role in this process and their values are consistent, within the Standard Model
interpretation, with a light Higgs boson with mass lower than about 200 GeV. If
new physics were responsible for the mechanism of electroweak symmetry
breaking, there would, quite generally, be modifications to this prediction
induced by the non-standard contributions to the precision electroweak
observables. In this article, we analyze the experimental signatures of a heavy
Higgs boson at linear colliders. We show that a linear collider, with center of
mass energy \sqrt{s} <= 1 TeV, would be very useful to probe the basic
ingredients of well motivated heavy Higgs boson models: a relatively heavy
SM-like Higgs, together with either extra scalar or fermionic degrees of
freedom, or with the mixing of the third generation quarks with non-standard
heavy quark modes.Comment: 21 page
Beauty is Distractive: Particle production during multifield inflation
We consider a two-dimensional model of inflation, where the inflationary
trajectory is "deformed" by a grazing encounter with an Extra Species/Symmetry
Point (ESP) after the observable cosmological scales have left the Hubble
radius. The encounter entails a sudden production of particles, whose
backreaction causes a bending of the trajectory and a temporary decrease in
speed, both of which are sensitive to initial conditions. This "modulated"
effect leads to an additional contribution to the curvature perturbation, which
can be dominant if the encounter is close. We compute associated
non-Gaussianities, the bispectrum and its scale dependence as well as the
trispectrum, which are potentially detectable in many cases. In addition, we
consider a direct modulation of the coupling to the light field at the ESP via
a modulaton field, a mixed scenario whereby the modulaton is identified with a
second inflaton, and an extended Extra Species Locus (ESL); all of these
scenarios lead to similar additional contributions to observables. We conclude
that inflaton interactions throughout inflation are strongly constrained if
primordial non-Gaussianities remain unobserved in current experiments such as
PLANCK. If they are observed, an ESP encounter leaves additional signatures on
smaller scales which may be used to identify the model.Comment: 41 pages, 6 figures; v2: references and minor clarifications added,
conclusions unchange
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Quantum fluctuations of charge order induce phonon softening in a superconducting cuprate
Quantum phase transitions play an important role in shaping the phase diagram
of high-temperature cuprate superconductors. These cuprates possess intertwined
orders which interact strongly with superconductivity. However, the evidence
for the quantum critical point associated with the charge order in the
superconducting phase remains elusive. Here we show the short-range charge
orders and the spectral signature of the quantum fluctuations in
LaSrCuO (LSCO) near the optimal doping using high-resolution
resonant inelastic X-ray scattering. On performing calculations through a
diagrammatic framework, we discovered that the charge correlations
significantly soften several branches of phonons. These results elucidate the
role of charge order in the LSCO compound, providing evidence for quantum
critical scaling and discommensurations associated with charge order
Quantum fluctuations of charge order induce phonon softening in a superconducting cuprate
Quantum phase transitions play an important role in shaping the phase diagram
of high-temperature cuprate superconductors. These cuprates possess intertwined
orders which interact strongly with superconductivity. However, the evidence
for the quantum critical point associated with the charge order in the
superconducting phase remains elusive. Here we show the short-range charge
orders and the spectral signature of the quantum fluctuations in
LaSrCuO (LSCO) near the optimal doping using high-resolution
resonant inelastic X-ray scattering. On performing calculations through a
diagrammatic framework, we discovered that the charge correlations
significantly soften several branches of phonons. These results elucidate the
role of charge order in the LSCO compound, providing evidence for quantum
critical scaling and discommensurations associated with charge order
Vortex dynamics for two-dimensional XY models
Two-dimensional XY models with resistively shunted junction (RSJ) dynamics
and time dependent Ginzburg-Landau (TDGL) dynamics are simulated and it is
verified that the vortex response is well described by the Minnhagen
phenomenology for both types of dynamics. Evidence is presented supporting that
the dynamical critical exponent in the low-temperature phase is given by
the scaling prediction (expressed in terms of the Coulomb gas temperature
and the vortex renormalization given by the dielectric constant
) both for RSJ and TDGL
and that the nonlinear IV exponent a is given by a=z+1 in the low-temperature
phase. The results are discussed and compared with the results of other recent
papers and the importance of the boundary conditions is emphasized.Comment: 21 pages including 15 figures, final versio
Discrete symmetries, invisible axion and lepton number symmetry in an economic 3-3-1 model
We show that Peccei-Quinn and lepton number symmetries can be a natural
outcome in a 3-3-1 model with right-handed neutrinos after imposing a Z_11 x
Z_2 symmetry. This symmetry is suitably accommodated in this model when we
augmented its spectrum by including merely one singlet scalar field. We work
out the breaking of the Peccei-Quinn symmetry, yielding the axion, and study
the phenomenological consequences. The main result of this work is that the
solution to the strong CP problem can be implemented in a natural way, implying
an invisible axion phenomenologically unconstrained, free of domain wall
formation and constituting a good candidate for the cold dark matter.Comment: 17 pages, Revtex
Microwave Surface Impedance of YBCO:123 crystals: Experiment and comparison to a d-wave model
We present measurements of the microwave surface resistance Rs and the
penetration depth lambda of YBCO:123 crystals. At low T obeys lambda(T) a
polynomial behavior, while Rs displays a characteristic non-monotonic
T-dependence.
A detailed comparison of the experimental data is made to a model of d-wave
superconductivity which includes both elastic and inelastic scattering. While
the model reproduces the general features of the experimental data, three
aspects of the parameters needed are worth noting. The elastic scattering rate
required to fit the data is much smaller than measured from the normal state,
the scattering phase shifts have to be close to pi/2 and a strong coupling
value of the gap parameter 2\Delta(0)/kTc = 6 is needed. On the experimental
side the uncertainties regarding the material parameters lambda(0) and
Rs,res(0) further complicate a quantitative comparison.
For one sample does Rs,res(0) agree with the intrinsic value which results
from the d-wave model.Comment: uuencoded tar.Z, 11 pages with 5 figures, used style files: elsart
and graphicx, PS-file available at http://sagar.cas.neu.edu/preprints.htm
Unitary Standard Model from Spontaneous Dimensional Reduction and Weak Boson Scattering at the LHC
Spontaneous dimensional reduction (SDR) is a striking phenomenon predicted by
a number of quantum gravity approaches which all indicate that the spacetime
dimensions get reduced at high energies. In this work, we formulate an
effective theory of electroweak interactions based upon the standard model,
incorporating the spontaneous reduction of space-dimensions at TeV scale. The
electroweak gauge symmetry is nonlinearly realized with or without a Higgs
boson. We demonstrate that the SDR ensures good high energy behavior and
predicts unitary weak boson scattering. For a light Higgs boson of mass 125GeV,
the TeV-scale SDR gives a natural solution to the hierarchy problem. Such a
light Higgs boson can have induced anomalous gauge couplings from the TeV-scale
SDR. We find that the corresponding WW scattering cross sections become unitary
at TeV scale, but exhibit different behaviors from that of the 4d standard
model. These can be discriminated by the WW scattering experiments at the LHC.Comment: 38pp, Eur.Phys.J.(in Press); extended discussions for testing non-SM
Higgs boson(125GeV) via WW scattering; minor clarifications added; references
added; a concise companion is given in the short PLB letter arXiv:1301.457
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