3,751 research outputs found
An Exact Bosonization Rule for c=1 Noncritical String Theory
We construct a string field theory for c=1 noncritical strings using the loop
variables as the string field. We show how one can express the nonrelativistic
free fermions which describes the theory, in terms of these string fields.Comment: 17 pages, to appear in JHE
Naked Singularity and Thunderbolt
We consider quantum theoretical effects of the sudden change of the boundary
conditions which mimics the occurrence of naked singularities. For a simple
demonstration, we study a massless scalar field in -dimensional
Minkowski spacetime with finite spatial interval. We calculate the vacuum
expectation value of the energy-momentum tensor and explicitly show that
singular wave or {\em thunderbolt} appears along the Cauchy horizon. The
thunderbolt possibly destroys the Cauchy horizon if its backreaction on the
geometry is taken into account, leading to quantum restoration of the global
hyperbolicity. The result of the present work may also apply to the situation
that a closed string freely oscillating is traveling to a brane and changes
itself to an open string pinned-down by the ends satisfying the Dirichlet
boundary conditions on the brane.Comment: 12 pages, 1 figure, references added, to appear in Phys. Rev.
Dynamics in Stationary, Non-Globally Hyperbolic Spacetimes
Classically, the dynamics in a non-globally hyperbolic spacetime is ill
posed. Previously, a prescription was given for defining dynamics in static
spacetimes in terms of a second order operator acting on a Hilbert space
defined on static slices. The present work extends this result by giving a
similar prescription for defining dynamics in stationary spacetimes obeying
certain mild assumptions. The prescription is defined in terms of a first order
operator acting on a different Hilbert space from the one used in the static
prescription. It preserves the important properties of the earlier one: the
formal solution agrees with the Cauchy evolution within the domain of
dependence, and smooth data of compact support always give rise to smooth
solutions. In the static case, the first order formalism agrees with second
order formalism (using specifically the Friedrichs extension). Applications to
field quantization are also discussed.Comment: 18 pages, 1 figure, AMSLaTeX; v2: expanded discussion of field
quantization, new Proposition 3.1, revised Theorem 4.2, corrected typos, and
updated reference
Quantum mechanics without spacetime II : noncommutative geometry and the free point particle
In a recent paper we have suggested that a formulation of quantum mechanics
should exist, which does not require the concept of time, and that the
appropriate mathematical language for such a formulation is noncommutative
differential geometry. In the present paper we discuss this formulation for the
free point particle, by introducing a commutation relation for a set of
noncommuting coordinates. The sought for background independent quantum
mechanics is derived from this commutation relation for the coordinates. We
propose that the basic equations are invariant under automorphisms which map
one set of coordinates to another- this is a natural generalization of
diffeomorphism invariance when one makes a transition to noncommutative
geometry. The background independent description becomes equivalent to standard
quantum mechanics if a spacetime manifold exists, because of the proposed
automorphism invariance. The suggested basic equations also give a quantum
gravitational description of the free particle.Comment: 8 page
Origin of second-harmonic generation in the incommensurate phase of K2SeO4
We show that a ferroelectric phase transition takes place in the
incommensurate phase of the K2SeO4 crystal. The ferroelectric character of the
IC phase explains the second-harmonic generation observed in the corresponding
temperature range.Comment: 5 pages, 1 figur
Upper Bounds for the Critical Car Densities in Traffic Flow Problems
In most models of traffic flow, the car density is the only free
parameter in determining the average car velocity . The
critical car density , which is defined to be the car density separating
the jamming phase (with ) and the moving phase (with
), is an important physical quantity to investigate. By
means of simple statistical argument, we show that for the
Biham-Middleton-Levine model of traffic flow in two or higher spatial
dimensions. In particular, we show that in 2 dimension and
in () dimensions.Comment: REVTEX 3.0, 5 pages with 1 figure appended at the back, Minor
revision, to be published in the Sept issue of J.Phys.Soc.Japa
Significance of myocardial tenascin-C expression in left ventricular remodelling and long-term outcome in patients with dilated cardiomyopathy
Aim Dilated cardiomyopathy (DCM) has a variety of causes, and no useful approach to predict left ventricular (LV) remodelling and long-term outcome has yet been established. Myocardial tenascin-C (TNC) is known to appear under pathological conditions, possibly to regulate cardiac remodelling. The aim of this study was to clarify the significance of myocardial TNC expression in LV remodelling and the long-term outcome in DCM. Methods and results One hundred and twenty-three consecutive DCM patients who underwent endomyocardial biopsy for initial diagnosis were studied. Expression of TNC in biopsy sections was analysed immunohistochemically to quantify the ratio of the TNC-positive area to the whole myocardial tissue area (TNC area). Clinical parameters associated with TNC area were investigated. The patients were divided into two groups based on receiver operating characteristic analysis of TNC area to predict death: high TNC group with TNC area ≥2.3% (22 patients) and low TNC group with TNC area <2.3% (101 patients). High TNC was associated with diabetes mellitus. Comparing echocardiographic findings between before and 9 months after endomyocardial biopsy, the low TNC group was associated with decreased LV end-diastolic diameter and increased LV ejection fraction, whereas the high TNC group was not. Survival analysis revealed a worse outcome in the high TNC group than in the low TNC group (P < 0.001). Multivariable Cox regression analysis revealed that TNC area was independently associated with poor outcome (HR = 1.347, P = 0.032). Conclusions Increased myocardial TNC expression was associated with worse LV remodeling and long-term outcome in DCM
Stability in Designer Gravity
We study the stability of designer gravity theories, in which one considers
gravity coupled to a tachyonic scalar with anti-de Sitter boundary conditions
defined by a smooth function W. We construct Hamiltonian generators of the
asymptotic symmetries using the covariant phase space method of Wald et al.and
find they differ from the spinor charges except when W=0. The positivity of the
spinor charge is used to establish a lower bound on the conserved energy of any
solution that satisfies boundary conditions for which has a global minimum.
A large class of designer gravity theories therefore have a stable ground
state, which the AdS/CFT correspondence indicates should be the lowest energy
soliton. We make progress towards proving this, by showing that minimum energy
solutions are static. The generalization of our results to designer gravity
theories in higher dimensions involving several tachyonic scalars is discussed.Comment: 29 page
First-Principles Study of Electronic Structure in -(BEDT-TTF)I at Ambient Pressure and with Uniaxial Strain
Within the framework of the density functional theory, we calculate the
electronic structure of -(BEDT-TTF)I at 8K and room temperature
at ambient pressure and with uniaxial strain along the - and -axes. We
confirm the existence of anisotropic Dirac cone dispersion near the chemical
potential. We also extract the orthogonal tight-binding parameters to analyze
physical properties. An investigation of the electronic structure near the
chemical potential clarifies that effects of uniaxial strain along the a-axis
is different from that along the b-axis. The carrier densities show
dependence at low temperatures, which may explain the experimental findings not
only qualitatively but also quantitatively.Comment: 10 pages, 7 figure
Dynamics of a string coupled to gravitational waves - Gravitational wave scattering by a Nambu-Goto straight string
We study the perturbative dynamics of an infinite gravitating Nambu-Goto
string within the general-relativistic perturbation framework. We develop the
gauge invariant metric perturbation on a spacetime containing a
self-gravitating straight string with a finite thickness and solve the
linearized Einstein equation. In the thin string case, we show that the string
does not emit gravitational waves by its free oscillation in the first order
with respect to its oscillation amplitude, nevertheless the string actually
bends when the incidental gravitational waves go through it.Comment: Published in Physical Review D. Some explanations are changed to
clarify our point
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