3,194 research outputs found

### Quantum Effective Action in Spacetimes with Branes and Boundaries: Diffeomorphism Invariance

We construct a gauge-fixing procedure in the path integral for gravitational
models with branes and boundaries. This procedure incorporates a set of gauge
conditions which gauge away effectively decoupled diffeomorphisms acting in the
$(d+1)$-dimensional bulk and on the $d$-dimensional brane. The corresponding
gauge-fixing factor in the path integral factorizes as a product of the bulk
and brane (surface-theory) factors. This factorization underlies a special bulk
wavefunction representation of the brane effective action. We develop the
semiclassical expansion for this action and explicitly derive it in the
one-loop approximation. The one-loop brane effective action can be decomposed
into the sum of the gauge-fixed bulk contribution and the contribution of the
pseudodifferential operator of the brane-to-brane propagation of quantum
gravitational perturbations. The gauge dependence of these contributions is
analyzed by the method of Ward identities. By the recently suggested method of
the Neumann-Dirichlet reduction the bulk propagator in the semiclassical
expansion is converted to the Dirichlet boundary conditions preferable from the
calculational viewpoint.Comment: 37 pages, LaTe

### From Peierls brackets to a generalized Moyal bracket for type-I gauge theories

In the space-of-histories approach to gauge fields and their quantization,
the Maxwell, Yang--Mills and gravitational field are well known to share the
property of being type-I theories, i.e. Lie brackets of the vector fields which
leave the action functional invariant are linear combinations of such vector
fields, with coefficients of linear combination given by structure constants.
The corresponding gauge-field operator in the functional integral for the
in-out amplitude is an invertible second-order differential operator. For such
an operator, we consider advanced and retarded Green functions giving rise to a
Peierls bracket among group-invariant functionals. Our Peierls bracket is a
Poisson bracket on the space of all group-invariant functionals in two cases
only: either the gauge-fixing is arbitrary but the gauge fields lie on the
dynamical sub-space; or the gauge-fixing is a linear functional of gauge
fields, which are generic points of the space of histories. In both cases, the
resulting Peierls bracket is proved to be gauge-invariant by exploiting the
manifestly covariant formalism. Moreover, on quantization, a gauge-invariant
Moyal bracket is defined that reduces to i hbar times the Peierls bracket to
lowest order in hbar.Comment: 14 pages, Late

### Limitations of the mean field slave-particle approximations

We show that the transformation properties of the mean field slave
boson/fermion order parameters under an action of the global SU(2) group impose
certain restrictions on their applications to describe the phase diagram of the
t-J model.Comment: to appear in Phys. Rev.

### A geometric approach to scalar field theories on the supersphere

Following a strictly geometric approach we construct globally supersymmetric
scalar field theories on the supersphere, defined as the quotient space
$S^{2|2} = UOSp(1|2)/\mathcal{U}(1)$. We analyze the superspace geometry of the
supersphere, in particular deriving the invariant vielbein and spin connection
from a generalization of the left-invariant Maurer-Cartan form for Lie groups.
Using this information we proceed to construct a superscalar field action on
$S^{2|2}$, which can be decomposed in terms of the component fields, yielding a
supersymmetric action on the ordinary two-sphere. We are able to derive
Lagrange equations and Noether's theorem for the superscalar field itself.Comment: 38 pages, 1 figur

### Self-force on a scalar charge in radial infall from rest using the Hadamard-WKB expansion

We present an analytic method based on the Hadamard-WKB expansion to
calculate the self-force for a particle with scalar charge that undergoes
radial infall in a Schwarzschild spacetime after being held at rest until a
time t = 0. Our result is valid in the case of short duration from the start.
It is possible to use the Hadamard-WKB expansion in this case because the value
of the integral of the retarded Green's function over the particle's entire
past trajectory can be expressed in terms of two integrals over the time period
that the particle has been falling. This analytic result is expected to be
useful as a check for numerical prescriptions including those involving mode
sum regularization and for any other analytical approximations to self-force
calculations.Comment: 22 pages, 2 figures, Physical Review D version along with the
corrections given in the erratu

### Non-Perturbative One-Loop Effective Action for Electrodynamics in Curved Spacetime

In this paper we explicitly evaluate the one-loop effective action in four
dimensions for scalar and spinor fields under the influence of a strong,
covariantly constant, magnetic field in curved spacetime. In the framework of
zeta function regularization, we find the one-loop effective action to all
orders in the magnetic field up to linear terms in the Riemannian curvature. As
a particular case, we also obtain the one-loop effective action for massless
scalar and spinor fields. In this setting, we found that the vacuum energy of
charged spinors with small mass becomes very large due entirely by the
gravitational correction.Comment: LaTeX, 23 page

### Analysis and measurement of electromagnetic scattering by pyramidal and wedge absorbers

By modifying the reflection coefficients in the Uniform Geometrical Theory of Diffraction a solution that approximates the scattering from a dielectric wedge is found. This solution agrees closely with the exact solution of Rawlins which is only valid for a few minor cases. This modification is then applied to the corner diffraction coefficient and combined with an equivalent current and geometrical optics solutions to model scattering from pyramid and wedge absorbers. Measured results from 12 inch pyramid absorbers from 2 to 18 GHz are compared to calculations assuming the returns add incoherently and assuming the returns add coherently. The measured results tend to be between the two curves. Measured results from the 8 inch wedge absorber are also compared to calculations with the return being dominated by the wedge diffraction. The procedures for measuring and specifying absorber performance are discussed and calibration equations are derived to calculate a reflection coefficient or a reflectivity using a reference sphere. Shaping changes to the present absorber designs are introduced to improve performance based on both high and low frequency analysis. Some prototypes were built and tested

### Path-Integral Formulation of Pseudo-Hermitian Quantum Mechanics and the Role of the Metric Operator

We provide a careful analysis of the generating functional in the path
integral formulation of pseudo-Hermitian and in particular PT-symmetric quantum
mechanics and show how the metric operator enters the expression for the
generating functional.Comment: Published version, 4 page

### Teens Acting Against Violence (TAAV) Program Evaluation

Teens Acting Against Violence (TAAV) is a violence prevention and youth empowerment program at the Tundra Women’s Coalition (TWC) for teenagers living in Bethel, Alaska. Participation is voluntary and open for any interested teens aged 12-18. TWC and TAAV partnered with the University of Alaska Anchorage (UAA) Justice Center to conduct an evaluation of the TAAV program through a one-time survey of former and current adult members (over 18 years of age) of TAAV. Pursuant to TAAV objectives, the focus of the evaluation was placed on examining efforts in the areas of domestic violence and sexual assault prevention, building healthy relationships, encouraging sobriety, and suicide prevention.Tundra Women’s CoalitionTable of Contents /
Acknowledgments /
Executive Summary /
Section I. Introduction and Background /
Section II. Methodology /
Section III. Program Satisfaction /
Section IV. TAAV Staff /
Section V. Cultural Considerations /
Section VI. TAAV Activities /
Section VII. TAAV Impacts /
Section VIII. Life Skills /
Section IX. Self-perceptions /
Section X. Interpersonal Relationships /
Section XI. Bystander Intervention /
Section XII. High-risk Behaviors /
Section XIII. Member Feedback /
Section XIV. Conclusion and Recommendations /
Appendix A: TAAV Survey /
Appendix B: List of Survey Resources /
Appendix C: Data Table

### Higher order relations in Fedosov supermanifolds

Higher order relations existing in normal coordinates between affine
extensions of the curvature tensor and basic objects for any Fedosov
supermanifolds are derived. Representation of these relations in general
coordinates is discussed.Comment: 11 LaTex pages, no figure

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