287,440 research outputs found
A Possible Origin of Dark Energy
We discuss the possibility that the existence of dark energy may be due to
the presence of a spin zero field , either elementary or composite. In
the presence of other matter field, the transformation
constant can generate a negative pressure, like the cosmological constant. In
this picture, our universe can be thought as a very large bag, similar to the
much smaller MIT bag model for a single nucleon.Comment: 4 pages, no figure, typos correcte
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On the boundary-layer structure of patterns of convection in rectangular-planform containers
This paper considers the structure of steady-state solutions of the Swift–Hohenberg
equation describing convection in shallow rectangular-planform containers heated
from below. The lateral dimensions of the planform are assumed to be much larger
than the characteristic wavelength of convection. Results are restricted to patterns
composed of rolls orthogonal to the sides of the rectangle in which case convection
sets in at a critical value of the Rayleigh number in the form of rolls parallel to
the shorter sides. This primary bifurcation from the conductive state of no motion
produces a solution which subsequently undergoes a secondary bifurcation in which
the low-amplitude motion near the shorter sides is replaced locally by cross-rolls
perpendicular to the sides. This results in the formation of grain boundaries (or
domain boundaries) within the fluid which mark the division between the different
roll orientations.With increasing Rayleigh number the grain boundaries approach the sides of the
rectangle and a boundary-layer structure is formed. In the present paper the method
of matched asymptotic expansions is used to determine this boundary-layer structure
and to predict the location of the grain boundaries. An interesting feature of the
solution is that the grain boundaries develop significant curvature and bend into the
corners of the rectangle, where the local solution is also determined.The results are compared with numerical computations of the secondary solution
branch and with previous numerical and experimental work.</jats:p
Coherence and pairing in a doped Mott insulator: Application to the cuprates
The issues of single particle coherence and its interplay with singlet
pairing are studied within the slave boson gauge theory of a doped Mott
insulator. Prior work by one of us (T. Senthil, arXiv:0804.1555) showed that
the coherence scale below which Landau quasiparticles emerge is parametrically
lower than that identified in the slave boson mean field theory. Here we study
the resulting new non-fermi liquid intermediate temperature regime
characterized by a single particle scattering rate that is linear in
temperature (). In the presence of a d-wave pair amplitude this leads to a
pseudogap state with dependent Fermi arcs near the nodal direction.
Implications for understanding the cuprates are discussed.Comment: 4+ pages, 1 figure. Sequel to arXiv:0903.087
Models of Meson-Baryon Reactions in the Nucleon Resonance Region
It is shown that most of the models for analyzing meson-baryon reactions in
the nucleon resonance region can be derived from a Hamiltonian formulation of
the problem. An extension of the coupled-channel approach to include
channel is briefly described and some preliminary results for the
excitation are presented.Comment: Latex 13 pages; to appear in the Proceedings of Workshop on the
Physics of excited nucleons (NSTAR2004), Grenoble (France), March 24-27, 200
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Schwannomatosis of the Spinal Accessory Nerve: A Case Report.
Schwannomatosis is a distinct syndrome characterized by multiple peripheral nerve schwannomas that can be sporadic or familial in nature. Cases affecting the lower cranial nerves are infrequent. Here, the authors present a rare case of schwannomatosis affecting the left spinal accessory nerve. Upon genetic screening, an in-frame insertion at codon p.R177 of the Sox 10 gene was observed. There were no identifiable alterations in NF1, NF2, LZTR1, and SMARCB1. This case demonstrates a rare clinical presentation of schwannomatosis in addition to a genetic aberration that has not been previously reported in this disease context
Majorana Fermion Induced Resonant Andreev Reflection
We describe experimental signatures of Majorana fermion edge states, which
form at the interface between a superconductor and the surface of a topological
insulator. If a lead couples to the Majorana fermions through electron
tunneling, the Majorana fermions induce \textit{resonant} Andreev reflections
from the lead to the grounded superconductor. The linear tunneling conductance
is () if there is an even (odd) number of vortices in the
superconductor. Similar resonance occurs for tunneling into the zero mode in
the vortex core. We also study the current and noise of a two-lead device.Comment: 4 pages, 3 figures. Discussion on STM tunneling into the Majorana
zero mode in the vortex core is adde
Vortex description of the fractionalized phase in exciton bose condensate
As a sequel to the previous work [Phys. Rev. B 72, 235104 (2005)] we present
a vortex description of the fractionalized phase in exciton bose condensate.
Magnetic flux line and monopole of the 3+1D emergent U(1) gauge theory are
identified in the exciton picture. A bundle of vortex/anti-vortex pairs of all
flavors of excitons corresponds to the magnetic flux line and a point at which
the vortices and anti-vortices recombine is identified as magnetic monopole.
This completes the magnetic sector of the low energy excitation in the
fractionalized phase.Comment: 8 pages, 6 figures; clarification made in introductio
Cuprates as doped U(1) spin liquids
We explore theoretically the notion that the underdoped cuprates may be
viewed as doped U(1) spin liquid Mott insulators. We pursue a conceptually
clear version of this idea that naturally incorporates several aspects of the
phenomenology of the cuprates. We argue that the low doping region may be
fruitfully discussed in terms of the universal physics associated with a
chemical potential tuned Mott transition between a U(1) spin liquid insulator
and a d-wave superconductor. A precise characterization of the deconfinement in
the U(1) spin liquid is provided by the emergence of a conserved gauge flux.
This extra conservation law should hold at least approximately in the
underdoped materials. Experiments that could possibly detect this conserved
gauge flux are proposed.Comment: 11 pages, 7 figure
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