7,935 research outputs found
On the Universal Tachyon and Geometrical Tachyon
We study properties of non-BPS D(p+1)-brane in the background of k
NS5-branes, with one transverse direction compactified on a circle, from the
point of view of Dirac-Born-Infeld action. We present the analysis of two
different embedding of non-BPS D(p+1)-brane in given background and study the
classical solutions of given world-volume theory. We argue for the
configuration of a non-BPS D(p+1)-brane which allows us to find solutions of
the equations of motion that give unified descriptions of G and U-type branes.Comment: 24 pages, minor change
Orbital Compass Model as an Itinerant Electron System
Two-dimensional orbital compass model is studied as an interacting itinerant
electron model. A Hubbard-type tight-binding model, from which the orbital
compass model is derived in the strong coupling limit, is identified. This
model is analyzed by the random-phase approximation (RPA) and the
self-consistent RPA methods from the weak coupling. Anisotropy for the orbital
fluctuation in the momentum space is qualitatively changed by the on-site
Coulomb interaction. This result is explained by the fact that the dominant
fluctuation is changed from the intra-band nesting to the inter-band one by
increasing the interaction.Comment: 7 pages, 8 figure
Non-compact Mirror Bundles and (0,2) Liouville Theories
We study (0,2) deformations of N=2 Liouville field theory and its mirror
duality. A gauged linear sigma model construction of the ultraviolet theory
connects (0,2) deformations of Liouville field theory and (0,2) deformations of
N=2 SL(2,R)/U(1) coset model as a mirror duality. Our duality proposal from the
gauged linear sigma model completely agrees with the exact CFT analysis. In the
context of heterotic string compactifications, the deformation corresponds to
the introduction of a non-trivial gauge bundle. This non-compact
Landau-Ginzburg construction yields a novel way to study the gauge bundle
moduli for non-compact Calabi-Yau manifolds.Comment: 34 page
General Relativistic Hydrodynamic Simulations and Linear Analysis of the Standing Accretion Shock Instability around a Black Hole
We study the stability of standing shock waves in advection-dominated
accretion flows into a Schwarzschild black hole by 2D general relativistic
hydrodynamic simulations as well as linear analysis in the equatorial plane. We
demonstrate that the accretion shock is stable against axisymmetric
perturbations but becomes unstable to non-axisymmetric perturbations. The
results of dynamical simulations show good agreement with linear analysis on
the stability, oscillation and growing time scales. The comparison of different
wave-travel times with the growth time scales of the instability suggests that
the instability is likely to be of the Papaloizou-Pringle type, induced by the
repeated propagations of acoustic waves. However, the wavelengths of
perturbations are too long to clearly define the reflection point. By analyzing
the non-linear phase in the dynamical simulations, it is shown that quadratic
mode couplings precede the non-linear saturation. It is also found that not
only short-term random fluctuations by turbulent motions but also quasi
periodic oscillations take place on longer time scales in the non-linear phase.
We give some possible implications of the instability for quasi periodic
oscillations (QPOs) and the central engine for gamma ray bursts (GRBs).Comment: 34 pages, 11 figures, accepted in Ap
Observables and Correlators in Nonrelativistic ABJM Theory
Non-relativistic ABJM theory is defined by Galilean limit of mass-deformed
N=6 Chern-Simons theory. Holographic string theory dual to the theory is not
known yet. To understand features candidate gravity dual might exhibit, we
examine local and nonlocal physical observables and their correlations in the
non-relativistic ABJM theory. We show that gauge invariant local observables
correspond to zero-norm states and that correlation functions among them are
trivial. We also show that a particular class of nonlocal observables, Wilson
loops, are topological in the sense that their correlation functions coincide
with those of pure Chern-Simons theory. We argue that the theory is
nevertheless physical and illustrate several physical observables whose
correlation functions are nontrivial. We also study quantum aspects. We show
that Chern-Simons level is finitely renormalized and that dilatation operator
acting on spin chain is trivial at planar limit. These results all point to
string scale geometry of gravity dual and to intriguing topological and
tensionless nature of dual string defined on it.Comment: 1+30 pages, no figure, v2. typos fixed and references adde
Unexpected Dirac-Node Arc in the Topological Line-Node Semimetal HfSiS
We have performed angle-resolved photoemission spectroscopy on HfSiS, which
has been predicted to be a topological line-node semimetal with square Si
lattice. We found a quasi-two-dimensional Fermi surface hosting bulk nodal
lines, alongside the surface states at the Brillouin-zone corner exhibiting a
sizable Rashba splitting and band-mass renormalization due to many-body
interactions. Most notably, we discovered an unexpected Dirac-like dispersion
extending one-dimensionally in k space - the Dirac-node arc - near the bulk
node at the zone diagonal. These novel Dirac states reside on the surface and
could be related to hybridizations of bulk states, but currently we have no
explanation for its origin. This discovery poses an intriguing challenge to the
theoretical understanding of topological line-node semimetals.Comment: 5 pages, 4 figures (paper proper) + 2 pages, figures (supplemental
material
Algebraic varieties with automorphism groups of maximal rank
We confirm, to some extent, the belief that a projective variety X has the
largest number (relative to the dimension of X) of independent commuting
automorphisms of positive entropy only when X is birational to a complex torus
or a quotient of a torus. We also include an addendum to an early paper though
it is not used in the present paper.Comment: Mathematische Annalen (to appear
Space laser interferometers can determine the thermal history of the early Universe
It is shown that space-based gravitational wave detectors such as DECIGO
and/or Big Bang Observer (BBO) will provide us with invaluable information on
the cosmic thermal history after inflation and they will be able to determine
the reheat temperature provided that it lies in the range preferred by
the cosmological gravitino problem, GeV. Therefore it is
strongly desired that they will be put into practice as soon as possible.Comment: 5 page
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