1,396 research outputs found
Non-trivial classical backgrounds with vanishing quantum corrections
Vacuum polarization and particle production effects in classical
electromagnetic and gravitational backgrounds can be studied by the effective
lagrangian method. Background field configurations for which the effective
lagrangian is zero are special in the sense that the lowest order quantum
corrections vanishes for such configurations. We propose here the conjecture
that there will be neither particle production nor vacuum polarization in
classical field configurations for which all the scalar invariants are zero. We
verify this conjecture, by explicitly evaluating the effective lagrangian, for
non-trivial electromagnetic and gravitational backgrounds with vanishing scalar
invariants. The implications of this result are discussed.Comment: 20 pages, Revtex, Accepted for publication in Physical Review
The eightfold way to dissipation
We provide a complete characterization of hydrodynamic transport consistent
with the second law of thermodynamics at arbitrary orders in the gradient
expansion. A key ingredient in facilitating this analysis is the notion of
adiabatic hydrodynamics, which enables isolation of the genuinely dissipative
parts of transport. We demonstrate that most transport is adiabatic.
Furthermore, of the dissipative part, only terms at the leading order in
gradient expansion are constrained to be sign-definite by the second law (as
has been derived before).Comment: 5 pages, 1 figure. v2: minor clarifications. v3: minor changes. title
in published version differ
Schwinger-Keldysh formalism II: Thermal equivariant cohomology
Causally ordered correlation functions of local operators in near-thermal
quantum systems computed using the Schwinger-Keldysh formalism obey a set of
Ward identities. These can be understood rather simply as the consequence of a
topological (BRST) algebra, called the universal Schwinger-Keldysh
superalgebra, as explained in our companion paper arXiv:1610.01940. In the
present paper we provide a mathematical discussion of this topological algebra.
In particular, we argue that the structures can be understood in the language
of extended equivariant cohomology. To keep the discussion self-contained, we
provide a basic review of the algebraic construction of equivariant cohomology
and explain how it can be understood in familiar terms as a superspace gauge
algebra. We demonstrate how the Schwinger-Keldysh construction can be
succinctly encoded in terms a thermal equivariant cohomology algebra which
naturally acts on the operator (super)-algebra of the quantum system. The main
rationale behind this exploration is to extract symmetry statements which are
robust under renormalization group flow and can hence be used to understand
low-energy effective field theory of near-thermal physics. To illustrate the
general principles, we focus on Langevin dynamics of a Brownian particle,
rephrasing some known results in terms of thermal equivariant cohomology. As
described elsewhere, the general framework enables construction of effective
actions for dissipative hydrodynamics and could potentially illumine our
understanding of black holes.Comment: 72 pages; v2: fixed typos. v3: minor clarifications and improvements
to non-equilbirum work relations discussion. v4: typos fixed. published
versio
Exact Geosedics and Shortest Paths on Polyhedral Surface
We present two algorithms for computing distances along a non-convex polyhedral surface. The first algorithm computes exact minimal-geodesic distances and the second algorithm combines these distances to compute exact shortest-path distances along the surface. Both algorithms have been extended to compute the exact minimalgeodesic paths and shortest paths. These algorithms have been implemented and validated on surfaces for which the correct solutions are known, in order to verify the accuracy and to measure the run-time performance, which is cubic or less for each algorithm. The exact-distance computations carried out by these algorithms are feasible for large-scale surfaces containing tens of thousands of vertices, and are a necessary component of near-isometric surface flattening methods that accurately transform curved manifolds into flat representations.National Institute for Biomedical Imaging and Bioengineering (R01 EB001550
Thermal out-of-time-order correlators, KMS relations, and spectral functions
We describe general features of thermal correlation functions in quantum
systems, with specific focus on the fluctuation-dissipation type relations
implied by the KMS condition. These end up relating correlation functions with
different time ordering and thus should naturally be viewed in the larger
context of out-of-time-ordered (OTO) observables. In particular, eschewing the
standard formulation of KMS relations where thermal periodicity is combined
with time-reversal to stay within the purview of Schwinger-Keldysh functional
integrals, we show that there is a natural way to phrase them directly in terms
of OTO correlators. We use these observations to construct a natural causal
basis for thermal n-point functions in terms of fully nested commutators. We
provide several general results which can be inferred from cyclic orbits of
permutations, and exemplify the abstract results using a quantum oscillator as
an explicit example.Comment: 36 pages + appendices. v2: minor changes + refs added. v3: minor
changes, published versio
Schwinger-Keldysh superspace in quantum mechanics
We examine, in a quantum mechanical setting, the Hilbert space representation
of the BRST symmetry associated with Schwinger-Keldysh path integrals. This
structure had been postulated to encode important constraints on influence
functionals in coarse-grained systems with dissipation, or in open quantum
systems. Operationally, this entails uplifting the standard Schwinger-Keldysh
two-copy formalism into superspace by appending BRST ghost degrees of freedom.
These statements were previously argued at the level of the correlation
functions. We provide herein a complementary perspective by working out the
Hilbert space structure explicitly. Our analysis clarifies two crucial issues
not evident in earlier works: firstly, certain background ghost insertions
necessary to reproduce the correct Schwinger-Keldysh correlators arise
naturally. Secondly, the Schwinger-Keldysh difference operators are
systematically dressed by the ghost bilinears, which turn out to be necessary
to give rise to a consistent operator algebra. We also elaborate on the
structure of the final state (which is BRST closed) and the future boundary
condition of the ghost fields.Comment: 30 page
Performance Comparison of Symmetric and Offset Reflector Antennas Adaptively Illuminated by Novel Triple Mode Feedhorn
Parabolic symmetric and offset reflector antennas adaptively illuminated using a novel triple-mode feedhorn (TE11+TM01+TE21) with different mode combinations and impedance and radiation performances are presented. The combination of the radiating modes in a feedhorn with proper amplitude and fixed phase values helps in electronically pointing the main beam of the radiating patterns such as that obtained in a beam-steering antenna with limited beam-scan range. This type of radiation performance virtually creates a displaced phase center location for the feedhorn, which, consequently, adaptively illuminates the reflector antenna surface. Impedance-matching bandwidths are preserved for both reflector antennas similar to the case of feedhorn alone. The copolarization gain and peak cross-polarization levels are far better with the offset reflector antenna than the symmetric reflector antenna. Such reflector antennas find applications in ground moving target indicator (GMTI) and space based radars. The investigation results are solely computed using FEKO full-wave analysis tool
Holographic thermal correlators: A tale of Fuchsian ODEs and integration contours
We analyze real-time thermal correlation functions of conserved currents in
holographic field theories using the grSK geometry, which provides a contour
prescription for their evaluation. We demonstrate its efficacy, arguing that
there are situations involving components of conserved currents, or derivative
interactions, where such a prescription is, in fact, essential. To this end, we
first undertake a careful analysis of the linearized wave equations in AdS
black hole backgrounds and identify the ramification points of the solutions as
a function of (complexified) frequency and momentum. All the equations we study
are Fuchsian with only regular singular points that for the most part are
associated with the geometric features of the background. Special features,
e.g., the appearance of apparent singular points at the horizon, whence
outgoing solutions end up being analytic, arise at higher codimension loci in
parameter space. Using the grSK geometry, we demonstrate that these apparent
singularities do not correspond to any interesting physical features in
higher-point functions. We also argue that the Schwinger-Keldysh collapse and
KMS conditions, implemented by the grSK geometry, continue to hold even in the
presence of such singularities. For charged black holes above a critical
charge, the energy density operator does not possess an exponentially growing
mode, associated with `pole-skipping' (from one such apparent singularity). Our
analysis suggests that the connection between the scrambling physics of black
holes and energy transport has, at best, a limited domain of validity.Comment: 35 pages plus appendice
PHARMACEUTICAL PREPARATION OF HINGULLOTHA PARADA
In Ayurveda Classics Rasaushadhi are prepare from Ashtasanskarita Parada because of its Rasayana guna and therapeutic properties, but it require great patience, time, skill and money hence a way has been given in the literature i.e. Hingulatha parada can be used in place of Astha sunskarita parada. Present study done with the aim of pharmaceutical Standardization of Extraction of Hingullotha Parada & study for usefulness of Hingullotha parada instead of Ashtasanskarita Parada in Ayurveda formulations.In the present study Extraction of Hingullotha Parada done three times then last three Sanskaras were done for Gunavardhana. After extraction of Hingullotha Parada % of yield was 42.61 % that is less it may be because of instrumental error.In Ashtasanskara of Parada last three Sanskar Bodhana, Niyamana & Deepan are having Gunavardhana property. Deepan sanskar improve Boobhuksha (bonding capacity) of Parada. After go through the classics it can be conclude that Hingullotha parada can be use instead of Astasanskarit Parada. And last three Sanskara can be doing for Gunavardhana (improving the Rasayana & Rogashamana property of Parada)
- …