1,653 research outputs found
Simplicial Chiral Models
Principal chiral models on a d-1 dimensional simplex are introduced and
studied analytically in the large limit. The and
models are explicitly solved. Relationship with standard lattice models and
with few-matrix systems in the double scaling limit are discussed.Comment: 6 pages, PHYZZ
Diffractive Higgs Production by AdS Pomeron Fusion
The double diffractive Higgs production at central rapidity is formulated in
terms of the fusion of two AdS gravitons/Pomerons first introduced by Brower,
Polchinski, Strassler and Tan in elastic scattering. Here we propose a simple
self-consistent holographic framework capable of providing phenomenologically
compelling estimates of diffractive cross sections at the LHC. As in the
traditional weak coupling approach, we anticipate that several phenomenological
parameters must be tested and calibrated through factorization for a
self-consistent description of other diffractive process such as total cross
sections, deep inelastic scattering and heavy quark production in the central
region.Comment: 53 pages, 8 figure
Survival probability of large rapidity gaps in QCD and N=4 SYM motivated model
In this paper we present a self consistent theoretical approach for the
calculation of the Survival Probability for central dijet production . These
calculations are performed in a model of high energy soft interactions based on
two ingredients:(i) the results of N=4 SYM, which at the moment is the only
theory that is able to deal with a large coupling constant; and (ii) the
required matching with high energy QCD. Assuming, in accordance with these
prerequisites, that soft Pomeron intercept is rather large and the slope of the
Pomeron trajectory is equal to zero, we derive analytical formulae that sum
both enhanced and semi-enhanced diagrams for elastic and diffractive
amplitudes. Using parameters obtained from a fit to the available experimental
data, we calculate the Survival Probability for central dijet production at
energies accessible at the LHC. The results presented here which include the
contribution of semi-enhanced and net diagrams, are considerably larger than
our previous estimates.Comment: 11 pages, 10 pictures in .eps file
Linear Sigma EFT for Nearly Conformal Gauge Theories
We construct a generalized linear sigma model as an effective field theory
(EFT) to describe nearly conformal gauge theories at low energies. The work is
motivated by recent lattice studies of gauge theories near the conformal
window, which have shown that the lightest flavor-singlet scalar state in the
spectrum () can be much lighter than the vector state () and
nearly degenerate with the PNGBs () over a large range of quark masses.
The EFT incorporates this feature. We highlight the crucial role played by the
terms in the potential that explicitly break chiral symmetry. The explicit
breaking can be large enough so that a limited set of additional terms in the
potential can no longer be neglected, with the EFT still weakly coupled in this
new range. The additional terms contribute importantly to the scalar and pion
masses. In particular, they relax the inequality , allowing for consistency with current lattice data.Comment: 9 pages, 1 figure, published versio
Lattice simulations with eight flavors of domain wall fermions in SU(3) gauge theory
We study an SU(3) gauge theory with Nf=8 degenerate flavors of light fermions
in the fundamental representation. Using the domain wall fermion formulation,
we investigate the light hadron spectrum, chiral condensate and electroweak S
parameter. We consider a range of light fermion masses on two lattice volumes
at a single gauge coupling chosen so that IR scales approximately match those
from our previous studies of the two- and six-flavor systems. Our results for
the Nf=8 spectrum suggest spontaneous chiral symmetry breaking, though fits to
the fermion mass dependence of spectral quantities do not strongly disfavor the
hypothesis of mass-deformed infrared conformality. Compared to Nf=2 we observe
a significant enhancement of the chiral condensate relative to the symmetry
breaking scale F, similar to the situation for Nf=6. The reduction of the S
parameter, related to parity doubling in the vector and axial-vector channels,
is also comparable to our six-flavor results
Stealth Dark Matter: Dark scalar baryons through the Higgs portal
We present a new model of "Stealth Dark Matter": a composite baryonic scalar
of an strongly-coupled theory with even . All mass scales
are technically natural, and dark matter stability is automatic without
imposing an additional discrete or global symmetry. Constituent fermions
transform in vector-like representations of the electroweak group that permit
both electroweak-breaking and electroweak-preserving mass terms. This gives a
tunable coupling of stealth dark matter to the Higgs boson independent of the
dark matter mass itself. We specialize to , and investigate the
constraints on the model from dark meson decay, electroweak precision
measurements, basic collider limits, and spin-independent direct detection
scattering through Higgs exchange. We exploit our earlier lattice simulations
that determined the composite spectrum as well as the effective Higgs coupling
of stealth dark matter in order to place bounds from direct detection,
excluding constituent fermions with dominantly electroweak-breaking masses. A
lower bound on the dark baryon mass GeV is obtained from the
indirect requirement that the lightest dark meson not be observable at LEP II.
We briefly survey some intriguing properties of stealth dark matter that are
worthy of future study, including: collider studies of dark meson production
and decay; indirect detection signals from annihilation; relic abundance
estimates for both symmetric and asymmetric mechanisms; and direct detection
through electromagnetic polarizability, a detailed study of which will appear
in a companion paper.Comment: 15 pages, 3 figures, citations added, typos fixed, minor
clarification
Unidirectional heterologous receptor desensitization between both the fMLP and C5a receptor and the ILâ8 receptor
During inflammation neutrophils receive multiple signals that are integrated, allowing a single modified response. One mechanism for this discrimination is receptor desensitization, a process whereby ligandâreceptor binding is disassociated from cell activation. We examined the effect of heterologous receptor desensitization on neutrophil Chemotaxis, calcium mobilization, and arachidonic acid production, using interleukinâ8 (ILâ8), C5a, and Nâformylâmethionylâleucylâphenylalanine (fMLP). We observed reciprocal inhibition with respect to Chemotaxis. We demonstrated that homologous desensitization, with respect to the mobilization of intracellular calcium stores, lasted approximately 15 min. Heterologous desensitization between the fMLP receptor and the C5a receptor was reciprocal; either stimulant would diminish the cells9 response to stimulation by the other for approximately 3â5 min. However, we observed a unidirectional heterologous desensitization of the ILâ8 receptor by both the fMLP and the C5a receptor. This unidirectional heterologous desensitization was observed with respect to both calcium mobilization and arachidonic acid production (i.e., prestimulation of the ILâ8 receptor had no effect on subsequent stimulation by either fMLP or C5a).Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141009/1/jlb0088.pd
Viscous fingering in liquid crystals: Anisotropy and morphological transitions
We show that a minimal model for viscous fingering with a nematic liquid
crystal in which anisotropy is considered to enter through two different
viscosities in two perpendicular directions can be mapped to a two-fold
anisotropy in the surface tension. We numerically integrate the dynamics of the
resulting problem with the phase-field approach to find and characterize a
transition between tip-splitting and side-branching as a function of both
anisotropy and dimensionless surface tension. This anisotropy dependence could
explain the experimentally observed (reentrant) transition as temperature and
applied pressure are varied. Our observations are also consistent with previous
experimental evidence in viscous fingering within an etched cell and
simulations of solidification.Comment: 12 pages, 3 figures. Submitted to PR
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