12,017 research outputs found

### Universal conductance in quantum wires in the presence of Umklapp scattering

The effects of Umklapp scattering on the zero-temperature conductance in
one-dimensional quantum wires are reexamined by taking into account both the
screening of external potential and the non-uniform chemical potential shift
due to electron-electron interaction. It is shown that in the case away from
half-filling the conductance is given by the universal value, $2e^2/h$, even in
the presence of Umklapp scattering, owing to these renormalization effects of
external potential. The conclusion is in accordance with the recent claim
obtained for the system with non-interacting leads being attached to a quantum
wire.Comment: 5 pages, to be published in Euro. Phys. J.

### String tension and glueball masses of SU(2) QCD from perfect action for monopoles and strings

We study the perfect monopole action as an infrared effective theory of SU(2)
QCD. It is transformed exactly into a lattice string model. Since the monopole
interactions are weak in the infrared SU(2) QCD, the string interactions become
strong. The strong coupling expansion of string model shows the quantum
fluctuation is small. The classical string tension is estimated analytically,
and we see it is very close to the quantum one in the SU(2) QCD. We also
discuss how to calculate the glueball mass in our model.Comment: LATTICE99(Confinement), 3 pages and 1 EPS figure

### Chain breaks and the susceptibility of Sr_2Cu_{1-x}Pd_xO_{3+\delta} and other doped quasi one-dimensional antiferromagnets

We study the magnetic susceptibility of one-dimensional S=1/2
antiferromagnets containing non-magnetic impurities which cut the chain into
finite segments. For the susceptibility of long anisotropic Heisenberg
chain-segments with open boundaries we derive a parameter-free result at low
temperatures using field theory methods and the Bethe Ansatz. The analytical
result is verified by comparing with Quantum-Monte-Carlo calculations. We then
show that the partitioning of the chain into finite segments can explain the
Curie-like contribution observed in recent experiments on
Sr_2Cu_{1-x}Pd_xO_{3+\delta}. Possible additional paramagnetic impurities seem
to play only a minor role.Comment: 4 pages, 3 figures, final versio

### The infrared-dark dust content of high redshift galaxies

We present a theoretical model aimed at explaining the IRX-$\beta$ relation
for high redshift (z >5) galaxies. Recent observations (Capak+2015;
Bouwens+2016) have shown that early Lyman Break Galaxies, although
characterized by a large UV attenuation (e.g. flat UV beta slopes), show a
striking FIR deficit, i.e. they are "infrared-dark". This marked deviation from
the local IRX-beta relation can be explained by the larger molecular gas
content of these systems. While dust in the diffuse ISM attains relatively high
temperatures (Td = 45 K for typical size a=0.1 um; smaller grains can reach Td
= 60 K), a sizable fraction of the dust mass is embedded in dense gas, and
therefore remains cold. If confirmed, the FIR deficit might represent a novel,
powerful indicator of the molecular content of high-z galaxies which can be
used to pre-select candidates for follow-up deep CO observations. Thus, high-z
CO line searches with ALMA might be much more promising than currently thought.Comment: 8 pages, 4 Figures, MNRAS Submitte

### Magnetohydrodynamic Simulations of A Rotating Massive Star Collapsing to A Black Hole

We perform two-dimensional, axisymmetric, magnetohydrodynamic simulations of
the collapse of a rotating star of 40 Msun and in the light of the collapsar
model of gamma-ray burst. Considering two distributions of angular momentum, up
to \sim 10^{17} cm^2/s, and the uniform vertical magnetic field, we investigate
the formation of an accretion disk around a black hole and the jet production
near the hole. After material reaches to the black hole with the high angular
momentum, the disk is formed inside a surface of weak shock. The disk becomes
in a quasi-steady state for stars whose magnetic field is less than 10^{10} G
before the collapse. We find that the jet can be driven by the magnetic fields
even if the central core does not rotate as rapidly as previously assumed and
outer layers of the star has sufficiently high angular momentum. The magnetic
fields are chiefly amplified inside the disk due to the compression and the
wrapping of the field. The fields inside the disk propagate to the polar region
along the inner boundary near the black hole through the Alfv{\'e}n wave, and
eventually drive the jet. The quasi-steady disk is not an advection-dominated
disk but a neutrino cooling-dominated one. Mass accretion rates in the disks
are greater than 0.01 Msun/sec with large fluctuations. The disk is transparent
for neutrinos. The dense part of the disk, which locates near the hole, emits
neutrino efficiently at a constant rate of < 8 \times 10^{51} erg/s. The
neutrino luminosity is much smaller than those from supernovae after the
neutrino burst.Comment: 42 pages, accepted for publication in the Astrophysical Journal. A
paper with higher-resolution figures available at
http://www.ec.knct.ac.jp/~fujimoto/collapsar/mhd-color.pd

### Quantum Disordered Ground States in Frustrated Antiferromagnets with Multiple Ring Exchange Interactions

We present a certain class of two-dimensional frustrated quantum Heisenberg
spin systems with multiple ring exchange interactions which are rigorously
demonstrated to have quantum disordered ground states without magnetic
long-range order. The systems considered in this paper are s=1/2
antiferromagnets on a honeycomb and square lattices, and an s=1 antiferromagnet
on a triangular lattice. We find that for a particular set of parameter values,
the ground state is a short-range resonating valence bond state or a valence
bond crystal state. It is shown that these systems are closely related to the
quantum dimer model introduced by Rokhsar and Kivelson as an effective
low-energy theory for valence bond states.Comment: 6 pages, 4 figure

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