7,677 research outputs found
Protecting unparticles from the MSSM Higgs sector
We construct a model of an unparticle sector consisting of a supersymmetric
SU(N) gauge theory with the number of flavors in the Seiberg conformal window.
We couple this sector to the MSSM via heavy messengers. The resulting low
energy theory has a Higgs coupling to unparticles. The Higgs vev drives the
hidden Seiberg sector to a new conformal fixed point. The coupling to the Higgs
mediates supersymmetry breaking to the Seiberg sector, and breaks conformal
invariance at a lower scale. The low energy theory contains light stable and
metastable mesons. Higgs decay into this sector gives signatures which are
similar to those of "hidden valley" models. Decays of the lightest superpartner
of standard model particles into the hidden sector reveal potentially
observable unparticle kinematics.Comment: References added. 11 pages, 4 figure
Mixed finite element formulation applied to shape optimization
The development presented introduces a general form of mixed formulation for the optimal shape design problem. The associated optimality conditions are easily obtained without resorting to highly elaborate mathematical developments. Also, the physical significance of the adjoint problem is clearly defined with this formulation
Dynamical Susceptibility in KDP-type Crysals above and below Tc II
The path probability method (PPM) in the tetrahedron-cactus approximation is
applied to the Slater-Takagi model with dipole-dipole interaction for
KH2PO4-type hydrogen-bonded ferroelectric crystals in order to derive a small
dip structure in the real part of dynamical susceptibility observed at the
transition temperature Tc. The dip structure can be ascribed to finite
relaxation times of electric dipole moments responsible for the first order
transition with contrast to the critical slowing down in the second order
transition. The light scattering intensity which is related to the imaginary
part of dynamical susceptibility is also calculated above and below the
transition temperature and the obtained central peak structure is consistent
with polarization fluctuation modes in Raman scattering experiments.Comment: 8 pages, 11 figure
Application of exchange Monte Carlo method to ordering dynamics
We apply the exchange Monte Carlo method to the ordering dynamics of the
three-state Potts model with the conserved order parameter. Even for the deeply
quenched case to low temperatures, we have observed a rapid domain growth; we
have proved the efficiency of the exchange Monte Carlo method for the ordering
process. The late-stage growth law has been found to be for
the case of conserved order parameter of three-component system.Comment: 7 pages including 5 eps figures, to appear in New J. Phys.
http://www.njp.or
Rotating string in doubled geometry with generalized isometries
In this paper, we first construct a globally well-defined non-geometric
background which contains several branes in type II string theory compactified
on a 7-torus. One of these branes is called 5^2_2, which is a codimension-2
object and has a non-trivial monodromy given by a T-duality transformation. The
geometry near the 5^2_2-brane is shown to approach the non-geometric background
constructed in arXiv:1004.2521. We then construct the solution of a fundamental
string rotating along a non-trivial cycle in the 5^2_2 background. Although the
background is not axisymmetric in the usual sense, we show that it is actually
axisymmetric as a doubled geometry by explicitly finding a generalized Killing
vector. We perform a generalized coordinate transformation into a system where
the generalized isometry is manifest, and show that the winding and momentum
charges of the string solution is explicitly conserved in that system.Comment: 32 pages, 5 figures; v2: typos corrected, to appear in Physical
Review D; v3 minor errors fixed, improvements and a reference added to
section 4.
Universal properties of highly frustrated quantum magnets in strong magnetic fields
The purpose of the present paper is two-fold. On the one hand, we review some
recent studies on the low-temperature strong-field thermodynamic properties of
frustrated quantum spin antiferromagnets which admit the so-called
localized-magnon eigenstates. One the other hand, we provide some complementary
new results. We focus on the linear independence of the localized-magnon
states, the estimation of their degeneracy with the help of auxiliary classical
lattice-gas models and the analysis of the contribution of these states to
thermodynamics.Comment: Paper based on the invited talk given by J. Richter at the
International Conference "Statistical Physics 2006. Condensed Matter: Theory
and Applications" dedicated to the 90th anniversary of Ilya Lifshitz
(Kharkiv, 11-15 September, 2006
Colloids in active fluids: Anomalous micro-rheology and negative drag
We simulate an experiment in which a colloidal probe is pulled through an
active nematic fluid. We find that the drag on the particle is non-Stokesian
(not proportional to its radius). Strikingly, a large enough particle in
contractile fluid (such as an actomyosin gel) can show negative viscous drag in
steady state: the particle moves in the opposite direction to the externally
applied force. We explain this, and the qualitative trends seen in our
simulations, in terms of the disruption of orientational order around the probe
particle and the resulting modifications to the active stress.Comment: 5 pages, 3 figure
Statistics of correlated percolation in a bacterial community
Signal propagation over long distances is a ubiquitous feature of multicellular communities, but cell-to-cell variability can cause propagation to be highly heterogeneous. Simple models of signal propagation in heterogenous media, such as percolation theory, can potentially provide a quantitative understanding of these processes, but it is unclear whether these simple models properly capture the complexities of multicellular systems. We recently discovered that in biofilms of the bacterium Bacillus subtilis, the propagation of an electrical signal is statistically consistent with percolation theory, and yet it is reasonable to suspect that key features of this system go beyond the simple assumptions of basic percolation theory. Indeed, we find here that the probability for a cell to signal is not independent from other cells as assumed in percolation theory, but instead is correlated with its nearby neighbors. We develop a mechanistic model, in which correlated signaling emerges from cell division, phenotypic inheritance, and cell displacement, that reproduces the experimentally observed correlations. We find that the correlations do not significantly affect the spatial statistics, which we rationalize using a renormalization argument. Moreover, the fraction of signaling cells is not constant in space, as assumed in percolation theory, but instead varies within and across biofilms. We find that this feature lowers the fraction of signaling cells at which one observes the characteristic power-law statistics of cluster sizes, consistent with our experimental results. We validate the model using a mutant biofilm whose signaling probability decays along the propagation direction. Our results reveal key statistical features of a correlated signaling process in a multicellular community. More broadly, our results identify extensions to percolation theory that do or do not alter its predictions and may be more appropriate for biological systems.P50 GM085764 - NIGMS NIH HHS; Howard Hughes Medical Institute; R01 GM121888 - NIGMS NIH HHSPublished versio
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