2,541 research outputs found
Proper time and path integral representations for the commutation function
On the example of the quantized spinor field, interacting with arbitrary
external electromagnetic field, the commutation function is studied. It is
shown that a proper time representation is available in any dimensions. Using
it, all the light cone singularities of the function are found explicitly,
generalizing the Fock formula in four dimensions, and a path integral
representation is constructed.Comment: 20 pages, LaTeX, uses pictex macro
Quantum gravity at a TeV and the renormalization of Newton's constant
We examine whether renormalization effects can cause Newton¿s constant to change dramatically with energy, perhaps even reducing the scale of quantum gravity to the TeV region without the introduction of extra dimensions. We examine a model that realizes this possibility and describe experimental signatures from the production of small black holes
Quantum Effective Action in Spacetimes with Branes and Boundaries
We construct quantum effective action in spacetime with branes/boundaries.
This construction is based on the reduction of the underlying Neumann type
boundary value problem for the propagator of the theory to that of the much
more manageable Dirichlet problem. In its turn, this reduction follows from the
recently suggested Neumann-Dirichlet duality which we extend beyond the tree
level approximation. In the one-loop approximation this duality suggests that
the functional determinant of the differential operator subject to Neumann
boundary conditions in the bulk factorizes into the product of its Dirichlet
counterpart and the functional determinant of a special operator on the brane
-- the inverse of the brane-to-brane propagator. As a byproduct of this
relation we suggest a new method for surface terms of the heat kernel
expansion. This method allows one to circumvent well-known difficulties in heat
kernel theory on manifolds with boundaries for a wide class of generalized
Neumann boundary conditions. In particular, we easily recover several lowest
order surface terms in the case of Robin and oblique boundary conditions. We
briefly discuss multi-loop applications of the suggested Dirichlet reduction
and the prospects of constructing the universal background field method for
systems with branes/boundaries, analogous to the Schwinger-DeWitt technique.Comment: LaTeX, 25 pages, final version, to appear in Phys. Rev.
Ultraviolet Divergences in Cosmological Correlations
A method is developed for dealing with ultraviolet divergences in
calculations of cosmological correlations, which does not depend on dimensional
regularization. An extended version of the WKB approximation is used to analyze
the divergences in these calculations, and these divergences are controlled by
the introduction of Pauli--Villars regulator fields. This approach is
illustrated in the theory of a scalar field with arbitrary self-interactions in
a fixed flat-space Robertson--Walker metric with arbitrary scale factor .
Explicit formulas are given for the counterterms needed to cancel all
dependence on the regulator properties, and an explicit prescription is given
for calculating finite regulator-independent correlation functions. The
possibility of infrared divergences in this theory is briefly considered.Comment: References added on various regularization methods. Improved
discussion of further issues. 26 pages, 1 figur
van Vleck determinants: geodesic focussing and defocussing in Lorentzian spacetimes
The van Vleck determinant is an ubiquitous object, arising in many physically
interesting situations such as: (1) WKB approximations to quantum time
evolution operators and Green functions. (2) Adiabatic approximations to heat
kernels. (3) One loop approximations to functional integrals. (4) The theory of
caustics in geometrical optics and ultrasonics. (5) The focussing and
defocussing of geodesic flows in Riemannian manifolds. While all of these
topics are interrelated, the present paper is particularly concerned with the
last case and presents extensive theoretical developments that aid in the
computation of the van Vleck determinant associated with geodesic flows in
Lorentzian spacetimes. {\sl A fortiori} these developments have important
implications for the entire array of topics indicated. PACS: 04.20.-q,
04.20.Cv, 04.60.+n. To appear in Physical Review D47 (1993) 15 March.Comment: plain LaTeX, 18 page
Updating Prior Beliefs based on Ambiguous Evidence
This paper investigates a problem where the solver must
firstly determine which of two possible causes are the source
of an effect where one cause has a historically higher
propensity to cause that effect. Secondly, they must update the
propensity of the two causes to produce the effect in light of
the observation. Firstly, we find an error commensurate with
the ‘double updating’ error observed within the polarisation
literature: individuals appear to first use their prior beliefs to
interpret the evidence, then use the interpreted form of the
evidence, rather than the raw form, when updating. Secondly,
we find an error where individuals convert from a
probabilistic representation of the evidence to a categorical
one and use this representation when updating. Both errors
have the effect of exaggerating the evidence in favour of the
solver’s prior belief and could lead to confirmation bias and
polarisation
The Fermion Self-Energy during Inflation
We compute the one loop fermion self-energy for massless Dirac + Einstein in
the presence of a locally de Sitter background. We employ dimensional
regularization and obtain a fully renormalized result by absorbing all
divergences with BPHZ counterterms. An interesting technical aspect of this
computation is the need for a noninvariant counterterm owing to the breaking of
de Sitter invariance by our gauge condition. Our result can be used in the
quantum-corrected Dirac equation to search for inflation-enhanced quantum
effects from gravitons, analogous to those which have been found for massless,
minimally coupled scalars.Comment: 63 pages, 3 figures (uses axodraw.sty), LaTeX 2epsilon. Revised
version (to appear in Classical and Quantum Gravity) corrects some typoes and
contains some new reference
Seasonal rainfall predictability over the Lake Kariba catchment area
The Lake Kariba catchment area in southern Africa has one of the most variable climates of any major river basin, with an extreme range of conditions across the catchment and through time. Marked seasonal and interannual fluctuations in rainfall are a significant aspect of the catchment. To determine the predictability of seasonal rainfall totals over the Lake Kariba catchment area, this study used the low-level atmospheric circulation (850 hPa geopotential height fields) of a coupled ocean-atmosphere general circulation model (CGCM) over southern Africa, statistically downscaled to gridded seasonal rainfall totals over the catchment. This downscaling configuration was used to retroactively forecast the 3-month rainfall seasons of September-October-November through February-March-April, over a 14-year independent test period extending from 1994. Retroactive forecasts are produced for lead times of up to 5 months and probabilistic forecast performances evaluated for extreme rainfall thresholds of the 25th and 75th percentile values of the climatological record. The verification of the retroactive forecasts shows that rainfall over the catchment is predictable at extended lead-times, but that predictability is primarily found for austral mid-summer rainfall. This season is also associated with the highest potential economic value that can be derived from seasonal forecasts. A forecast case study of a recent extreme rainfall season (2010/11) that lies outside of the verification period is presented as evidence of the statistical downscaling system’s operational capability.Keywords: Lake Kariba catchment, coupled ocean-atmosphere model, statistical downscaling, seasonal forecasting, economic valu
Superfield extended BRST quantization in general coordinates
We propose a superfield formalism of Lagrangian BRST-antiBRST quantization of
arbitrary gauge theories in general coordinates with the base manifold of
fields and antifields desribed in terms of both bosonic and fermionic
variables.Comment: LaTex, 10 page
Nonlinear couplings and tree amplitudes in gauge theories
Following a remark advanced by Feynman,we study the connection between the
form of the nonlinear vertices involving gauge particles and the Abelian gauge
invariance of physical tree amplitudes. We show that this requirement, together
with some natural assumptions, fixes uniquely the structure of the Yang-Mills
theory. However, the constraints imposed by the above property are not
sufficient to single out the gauge theory of gravitation.Comment: 12 pages. Requires macros RevTeX, prepictex, pictex, postpictex. TeX
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