925,913 research outputs found
Ghost Condensate Busting
Applying the Thomas-Fermi approximation to renormalizable field theories, we
construct ghost condensation models that are free of the instabilities
associated with violations of the null-energy condition.Comment: 9 pages, minor corrections, a reference added, the discussion on
consistency of the Thomas-Fermi approximation expanded, to appear in JCA
Constraints on Gravitation from Causality and Quantum Consistency
We examine the role of consistency with causality and quantum mechanics in
determining the properties of gravitation. We begin by examining two different
classes of interacting theories of massless spin 2 particles -- gravitons. One
involves coupling the graviton with the lowest number of derivatives to matter,
the other involves coupling the graviton with higher derivatives to matter,
making use of the linearized Riemann tensor. The first class requires an
infinite tower of terms for consistency, which is known to lead uniquely to
general relativity. The second class only requires a finite number of terms for
consistency, which appears as another class of theories of massless spin 2. We
recap the causal consistency of general relativity and show how this fails in
the second class for the special case of coupling to photons, exploiting
related calculations in the literature. In a companion paper [1] this result is
generalized to a much broader set of theories. Then, as a causal modification
of general relativity, we add light scalar particles and recap the generic
violation of universal free-fall they introduce and its quantum resolution.
This leads to a discussion of a special type of scalar-tensor theory; the
models. We show that, unlike general relativity, these models
do not possess the requisite counterterms to be consistent quantum effective
field theories. Together this helps to remove some of the central assumptions
made in deriving general relativity.Comment: 6 pages in double column format. V2: Updated towards published
versio
Observational Signatures and Non-Gaussianities of General Single Field Inflation
We perform a general study of primordial scalar non-Gaussianities in single
field inflationary models in Einstein gravity. We consider models where the
inflaton Lagrangian is an arbitrary function of the scalar field and its first
derivative, and the sound speed is arbitrary. We find that under reasonable
assumptions, the non-Gaussianity is completely determined by 5 parameters. In
special limits of the parameter space, one finds distinctive ``shapes'' of the
non-Gaussianity. In models with a small sound speed, several of these shapes
would become potentially observable in the near future. Different limits of our
formulae recover various previously known results.Comment: 53 pages, 5 figures; v3, minor revision, JCAP version; v4, numerical
coefficients corrected in Appendix B, discussion on consistency condition
revise
Observational Signatures and Non-Gaussianities of General Single Field Inflation
We perform a general study of primordial scalar non-Gaussianities in single
field inflationary models in Einstein gravity. We consider models where the
inflaton Lagrangian is an arbitrary function of the scalar field and its first
derivative, and the sound speed is arbitrary. We find that under reasonable
assumptions, the non-Gaussianity is completely determined by 5 parameters. In
special limits of the parameter space, one finds distinctive ``shapes'' of the
non-Gaussianity. In models with a small sound speed, several of these shapes
would become potentially observable in the near future. Different limits of our
formulae recover various previously known results.Comment: 53 pages, 5 figures; v3, minor revision, JCAP version; v4, numerical
coefficients corrected in Appendix B, discussion on consistency condition
revise
Oddness from Rigidness
We revisit the problem of constructing type IIA orientifolds on T^6/(Z2 x Z2)
which admit (non)-factorisable lattices. More concretely, we consider a (Z2 x
Z2') orientifold with torsion, where D6-branes wrap rigid 3-cycles. We derive
the model building rules and consistency conditions in the case where the
compactification lattice is non-factorisable. We show that in this class of
configurations, (semi) realistic models with an odd number of families can be
easily constructed, in contrast to compactifications where the D6-branes wrap
non-rigid cycles. We also show that an odd number of families can be obtained
in the factorisable case, without the need of tilted tori. We illustrate the
discussion by presenting three family Pati-Salam models with no chiral exotics
in both factorisable and non-factorisable toroidal compactifications.Comment: 20 page
The Bose Metal: gauge field fluctuations and scaling for field tuned quantum phase transitions
In this paper, we extend our previous discussion of the Bose metal to the
field tuned case. We point out that the recent observation of the metallic
state as an intermediate phase between the superconductor and the insulator in
the field tuned experiments on MoGe films is in perfect consistency with the
Bose metal scenario. We establish a connection between general dissipation
models and gauge field fluctuations and apply this to a discussion of scaling
across the quantum phase boundaries of the Bose metallic state. Interestingly,
we find that the Bose metal scenario implies a possible {\em two} parameter
scaling for resistivity across the Bose metal-insulator transition, which is
remarkably consistent with the MoGe data. Scaling at the superconductor-metal
transition is also proposed, and a phenomenolgical model for the metallic state
is discussed. The effective action of the Bose metal state is described and its
low energy excitation spectrum is found to be .Comment: 15 pages, 1 figur
Deformation Quantization of Nambu Mechanics
Phase Space is the framework best suited for quantizing superintegrable
systems--systems with more conserved quantities than degrees of freedom. In
this quantization method, the symmetry algebras of the hamiltonian invariants
are preserved most naturally, as illustrated on nonlinear -models,
specifically for Chiral Models and de Sitter -spheres. Classically, the
dynamics of superintegrable models such as these is automatically also
described by Nambu Brackets involving the extra symmetry invariants of them.
The phase-space quantization worked out then leads to the quantization of the
corresponding Nambu Brackets, validating Nambu's original proposal, despite
excessive fears of inconsistency which have arisen over the years. This is a
pedagogical talk based on hep-th/0205063 and hep-th/0212267, stressing points
of interpretation and care needed in appreciating the consistency of Quantum
Nambu Brackets in phase space. For a parallel discussion in Hilbert space, see
T Curtright's contribution in these Proceedings [hep-th 0303088].Comment: Invited talk by the first author at the Coral Gables Conference
(C02/12/11.2), Ft Lauderdale, Dec 2002. 14p, LateX2e, aipproc, amsfont
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