920 research outputs found
Scale Symmetry Breaking From Total Derivative Densities and the Cosmological Constant Problem
The use in the action integral of totally divergent densities in generally
coordinate invariant theories can lead to interesting mechanisms of spontaneous
symmetry breaking of scale invariance. With dependence in the action on a
metric independent density , in , we can define that gives a
new interesting mechanism for breaking scale symmetry in 4-D theories of
gravity plus matter fields, through the equations of
motion which lead to an integration constant the breaks the scale symmetry,
while introducing terms of the form , being the determinant of
the vierbein, being the Gauss Bonnet scalar and being scalar functions
of the fields transforming like (where c is a constant)
under a scale transformation. Such a term is invariant only up to a total
divergence and therefore leads to breaking of scale invariance due to
gravitational instantons. The topological density constructed out of gauge
field strengths
can be coupled to the dilaton field linearly to produce a scale invariant term
up to a total divergence. The scale symmetry can be broken by Yang Mills
instantons which lead to a very small vacuum energy for our Universe.Comment: Accepted for Publication in Physics Letters B, 15 page
Simple Scheme for Gauge Mediation
We present a simple scheme for constructing models that achieve successful
gauge mediation of supersymmetry breaking. In addition to our previous work [1]
that proposed drastically simplified models using metastable vacua of
supersymmetry breaking in vector-like theories, we show there are many other
successful models using various types of supersymmetry breaking mechanisms that
rely on enhanced low-energy U(1)_R symmetries. In models where supersymmetry is
broken by elementary singlets, one needs to assume U(1)_R violating effects are
accidentally small, while in models where composite fields break supersymmetry,
emergence of approximate low-energy U(1)_R symmetries can be understood simply
on dimensional grounds. Even though the scheme still requires somewhat small
parameters to sufficiently suppress gravity mediation, we discuss their
possible origins due to dimensional transmutation. The scheme accommodates a
wide range of the gravitino mass to avoid cosmological problems.Comment: 13 page
N=1 Non-Abelian Tensor Multiplet in Four Dimensions
We carry out the N=1 supersymmetrization of a physical non-Abelian tensor
with non-trivial consistent couplings in four dimensions. Our system has three
multiplets: (i) The usual non-Abelian vector multiplet (VM) (A_\mu{}^I,
\lambda^I), (ii) A non-Abelian tensor multiplet (TM) (B_{\mu\nu}{}^I, \chi^I,
\varphi^I), and (iii) A compensator vector multiplet (CVM) (C_\mu{}^I, \rho^I).
All of these multiplets are in the adjoint representation of a non-Abelian
group G. Unlike topological theory, all of our fields are propagating with
kinetic terms. The C_\mu{}^I-field plays the role of a Stueckelberg compensator
absorbed into the longitudinal component of B_{\mu\nu}{}^I. We give not only
the component lagrangian, but also a corresponding superspace reformulation,
reconfirming the total consistency of the system. The adjoint representation of
the TM and CVM is further generalized to an arbitrary real representation of
general SO(N) gauge group. We also couple the globally N=1 supersymmetric
system to supergravity, as an additional non-trivial confirmation.Comment: 18 pages, no figur
Non-Abelian Tensors with Consistent Interactions
We present a systematic method for constructing consistent interactions for a
tensor field of an arbitrary rank in the adjoint representation of an arbitrary
gauge group in any space-time dimensions. This method is inspired by the
dimensional reduction of Scherk-Schwarz, modifying field strengths with certain
Chern-Simons forms, together with modified tensorial gauge transformations. In
order to define a consistent field strength of a r-rank tensor
B_{\mu_1...\mu_r}^I in the adjoint representation, we need the multiplet
(B_{\mu_1...\mu_r}^I, B_{\mu_1...\mu_{r-1}}^{I J}, ..., B_\mu^{I_1...I_r},
B^{I_1... I_{r+1}}). The usual problem of consistency of the tensor field
equations is circumvented in this formulation.Comment: 15 pages, no figure
One-Dimensional Confinement and Enhanced Jahn-Teller Instability in LaVO
Ordering and quantum fluctuations of orbital degrees of freedom are studied
theoretically for LaVO in spin-C-type antiferromagnetic state. The
effective Hamiltonian for the orbital pseudospin shows strong one-dimensional
anisotropy due to the negative interference among various exchange processes.
This significantly enhances the instability toward lattice distortions for the
realistic estimate of the Jahn-Teller coupling by first-principle LDA+
calculations, instead of favoring the orbital singlet formation. This explains
well the experimental results on the anisotropic optical spectra as well as the
proximity of the two transition temperatures for spin and orbital orderings.Comment: 4 pages including 4 figure
A Model of Direct Gauge Mediation
We present a simple model of gauge mediation (GM) which does not have a
messenger sector or gauge singlet fields. The standard model gauge groups
couple directly to the sector which breaks supersymmetry dynamically. This is
the first phenomenologically viable example of this type in the literature.
Despite the direct coupling, the model can preserve perturbative gauge
unification. This is achieved by the inverted hierarchy mechanism which
generates a large scalar expectation value compared to the size of
supersymmetry breaking. There is no dangerous negative contribution to the
squark, slepton masses due to two-loop renormalization group equation. The
potentially non-universal supergravity contribution to the scalar masses can be
suppressed enough to maintain the virtue of the gauge mediation. The model is
completely chiral, and one does not need to forbid mass terms for the messenger
fields by hand. Beyond the simplicity of the model, it possesses cosmologically
desirable features compared to the original models of GM: an improved gravitino
and string moduli cosmology. The Polonyi problem is back unlike in the original
GM models, but is still much less serious than in hidden sector models.Comment: LaTeX, 12 page
Singularity of the Velocity Distribution Function in Molecular Velocity Space
We study the boundary singularity of the solutions to the Boltzmann equation in the kinetic theory. The solution has a jump discontinuity in the microscopic velocity ζ on the boundary and a secondary singularity of logarithmic type around the velocity tangential to the boundary, ζnâŒ0-, where ζn is the component of molecular velocity normal to the boundary, pointing to the gas. We demonstrate this secondary singularity by obtaining an asymptotic formula for the derivative of the solution on the boundary with respect to ζnn that diverges logarithmically when ζnâŒ0-. Our study is for the thermal transpiration problem between two plates for the hard sphere gases with sufficiently large Knudsen number and with the diffuse reflection boundary condition. The solution is constructed and its singularity is studied by an iteration procedure
X-Ray Fluctuations from Locally Unstable Advection-Dominated Disks
The response of advection-dominated accretion disks to local disturbances is
examined by one-dimensional numerical simulations. It is generally believed
that advection-dominated disks are thermally stable. We, however, find that any
disurbance added onto accretion flow at large radii does not decay so rapidly
that it can move inward with roughly the free-fall velocity. Although
disturbances continue to be present, the global disk structure will not be
modified largely. This can account for persistent hard X-ray emission with
substantial variations observed in active galactic nuclei and stellar black
hole candidates during the hard state. Moreover, when the disturbance reaches
the innermost parts, an acoustic wave emerges, propagating outward as a shock
wave. The resultant light variation is roughly (time) symmetric and is quite
reminiscent of the observed X-ray shots of Cygnus X-1.Comment: plain TeX, 11 pages, without figures; to be published in ApJ Lette
Security of EPR-based Quantum Cryptography against Incoherent Symmetric Attacks
We investigate a new strategy for incoherent eavesdropping in Ekert's
entanglement based quantum key distribution protocol. We show that under
certain assumptions of symmetry the effectiveness of this strategy reduces to
that of the original single qubit protocol of Bennett and Brassard
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