11,887 research outputs found
Towards a quantum theory of de Sitter space
We describe progress towards constructing a quantum theory of de Sitter space
in four dimensions. In particular we indicate how both particle states and
Schwarzschild de Sitter black holes can arise as excitations in a theory of a
finite number of fermionic oscillators. The results about particle states
depend on a conjecture about algebras of Grassmann variables, which we state,
but do not prove.Comment: JHEP3 LaTex - 19 page
Embedding the Pentagon
The Pentagon Model is an explicit supersymmetric extension of the Standard
Model, which involves a new strongly-interacting SU(5) gauge theory at
TeV-scale energies. We show that the Pentagon can be embedded into an SU(5) x
SU(5) x SU(5) gauge group at the GUT scale. The doublet-triplet splitting
problem, and proton decay compatible with experimental bounds, can be
successfully addressed in this context. The simplest approach fails to provide
masses for the lighter two generations of quarks and leptons; however, this
problem can be solved by the addition of a pair of antisymmetric tensor fields
and an axion.Comment: 39 page
Decoupling a Fermion Whose Mass Comes from a Yukawa Coupling: Nonperturbative Considerations
Perturbative analyses seem to suggest that fermions whose mass comes solely
from a Yukawa coupling to a scalar field can be made arbitrarily heavy, while
the scalar remains light. The effects of the fermion can be summarized by a
local effective Lagrangian for the light degrees of freedom. Using weak
coupling and large N techniques, we present a variety of models in which this
conclusion is shown to be false when nonperturbative variations of the scalar
field are considered. The heavy fermions contribute nonlocal terms to the
effective action for light degrees of freedom. This resolves paradoxes about
anomalous and nonanomalous symmetry violation in these models. Application of
these results to lattice gauge theory imply that attempts to decouple lattice
fermion doubles by the method of Swift and Smit cannot succeed, a result
already suggested by lattice calculations.Comment: 31 page
A Pyramid Scheme for Particle Physics
We introduce a new model, the Pyramid Scheme, of direct mediation of SUSY
breaking, which is compatible with the idea of Cosmological SUSY Breaking
(CSB). It uses the trinification scheme of grand unification and avoids
problems with Landau poles in standard model gauge couplings. It also avoids
problems, which have recently come to light, associated with rapid stellar
cooling due to emission of the pseudo Nambu-Goldstone Boson (PNGB) of
spontaneously broken hidden sector baryon number. With a certain pattern of
R-symmetry breaking masses, a pattern more or less required by CSB, the Pyramid
Scheme leads to a dark matter candidate that decays predominantly into leptons,
with cross sections compatible with a variety of recent observations. The dark
matter particle is not a thermal WIMP but a particle with new strong
interactions, produced in the late decay of some other scalar, perhaps the
superpartner of the QCD axion, with a reheat temperature in the TeV range. This
is compatible with a variety of scenarios for baryogenesis, including some
novel ones which exploit specific features of the Pyramid Scheme.Comment: JHEP Latex, 32 pages, 1 figur
Toward a Background Independent Quantum Theory of Gravity
Any canonical quantum theory can be understood to arise from the
compatibility of the statistical geometry of distinguishable observations with
the canonical Poisson structure of Hamiltonian dynamics. This geometric
perspective offers a novel, background independent non-perturbative formulation
of quantum gravity. We invoke a quantum version of the equivalence principle,
which requires both the statistical and symplectic geometries of canonical
quantum theory to be fully dynamical quantities. Our approach sheds new light
on such basic issues of quantum gravity as the nature of observables, the
problem of time, and the physics of the vacuum. In particular, the observed
numerical smallness of the cosmological constant can be rationalized in this
approach.Comment: Awarded Honorable Mention, 2004 Gravity Research Foundation Essay
Competition; 8 pages, LaTe
Algebras, Derivations and Integrals
In the context of the integration over algebras introduced in a previous
paper, we obtain several results for a particular class of associative algebras
with identity. The algebras of this class are called self-conjugated, and they
include, for instance, the paragrassmann algebras of order , the
quaternionic algebra and the toroidal algebras. We study the relation between
derivations and integration, proving a generalization of the standard result
for the Riemann integral about the translational invariance of the measure and
the vanishing of the integral of a total derivative (for convenient boundary
conditions). We consider also the possibility, given the integration over an
algebra, to define from it the integral over a subalgebra, in a way similar to
the usual integration over manifolds. That is projecting out the submanifold in
the integration measure. We prove that this is possible for paragrassmann
algebras of order , once we consider them as subalgebras of the algebra of
the matrices. We find also that the integration over the
subalgebra coincides with the integral defined in the direct way. As a
by-product we can define the integration over a one-dimensional Grassmann
algebra as a trace over matrices.Comment: 23 pages, few typos corrected. Final version to be published in
International Journal of Modern Physic
Model validation for a noninvasive arterial stenosis detection problem
Copyright @ 2013 American Institute of Mathematical SciencesA current thrust in medical research is the development of a non-invasive method for detection, localization, and characterization of an arterial stenosis (a blockage or partial blockage in an artery). A method has been proposed to detect shear waves in the chest cavity which have been generated by disturbances in the blood flow resulting from a stenosis. In order to develop this methodology further, we use both one-dimensional pressure and shear wave experimental data from novel acoustic phantoms to validate corresponding viscoelastic mathematical models, which were developed in a concept paper [8] and refined herein. We estimate model parameters which give a good fit (in a sense to be precisely defined) to the experimental data, and use asymptotic error theory to provide confidence intervals for parameter estimates. Finally, since a robust error model is necessary for accurate parameter estimates and confidence analysis, we include a comparison of absolute and relative models for measurement error.The National Institute of Allergy and Infectious Diseases, the Air Force Office of Scientific Research, the Deopartment of Education and the Engineering and Physical Sciences Research Council (EPSRC)
Is There A String Theory Landscape
We examine recent claims of a large set of flux compactification solutions of
string theory. We conclude that the arguments for AdS solutions are plausible.
The analysis of meta-stable dS solutions inevitably leads to situations where
long distance effective field theory breaks down. We then examine whether these
solutions are likely to lead to a description of the real world. We conclude
that one must invoke a strong version of the anthropic principle. We explain
why it is likely that this leads to a prediction of low energy supersymmetry
breaking, but that many features of anthropically selected flux
compactifications are likely to disagree with experiment.Comment: 39 pages, Latex, ``Terminology surrounding the anthropic principle
revised to conform with accepted usage. More history of the anthropic
principle included. Various references added.
Estimation of coefficients and boundary parameters in hyperbolic systems
Semi-discrete Galerkin approximation schemes are considered in connection with inverse problems for the estimation of spatially varying coefficients and boundary condition parameters in second order hyperbolic systems typical of those arising in 1-D surface seismic problems. Spline based algorithms are proposed for which theoretical convergence results along with a representative sample of numerical findings are given
Supersymmetric extension of Moyal algebra and its application to the matrix model
We construct operator representation of Moyal algebra in the presence of
fermionic fields. The result is used to describe the matrix model in Moyal
formalism, that treat gauge degrees of freedom and outer degrees of freedom
equally.Comment: to appear in Mod.Phys.Let
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