1,980 research outputs found
Noise Kernel in Stochastic Gravity and Stress Energy Bi-Tensor of Quantum Fields in Curved Spacetimes
The noise kernel is the vacuum expectation value of the (operator-valued)
stress-energy bi-tensor which describes the fluctuations of a quantum field in
curved spacetimes. It plays the role in stochastic semiclassical gravity based
on the Einstein-Langevin equation similar to the expectation value of the
stress-energy tensor in semiclassical gravity based on the semiclassical
Einstein equation. According to the stochastic gravity program, this two point
function (and by extension the higher order correlations in a hierarchy) of the
stress energy tensor possesses precious statistical mechanical information of
quantum fields in curved spacetime and, by the self-consistency required of
Einstein's equation, provides a probe into the coherence properties of the
gravity sector (as measured by the higher order correlation functions of
gravitons) and the quantum nature of spacetime. It reflects the low and medium
energy (referring to Planck energy as high energy) behavior of any viable
theory of quantum gravity, including string theory. It is also useful for
calculating quantum fluctuations of fields in modern theories of structure
formation and for backreaction problems in cosmological and black holes
spacetimes.
We discuss the properties of this bi-tensor with the method of
point-separation, and derive a regularized expression of the noise-kernel for a
scalar field in general curved spacetimes. One collorary of our finding is that
for a massless conformal field the trace of the noise kernel identically
vanishes. We outline how the general framework and results derived here can be
used for the calculation of noise kernels for Robertson-Walker and
Schwarzschild spacetimes.Comment: 22 Pages, RevTeX; version accepted for publication in PR
Quantum correlation functions and the classical limit
We study the transition from the full quantum mechanical description of
physical systems to an approximate classical stochastic one. Our main tool is
the identification of the closed-time-path (CTP) generating functional of
Schwinger and Keldysh with the decoherence functional of the consistent
histories approach. Given a degree of coarse-graining in which interferences
are negligible, we can explicitly write a generating functional for the
effective stochastic process in terms of the CTP generating functional. This
construction gives particularly simple results for Gaussian processes. The
formalism is applied to simple quantum systems, quantum Brownian motion,
quantum fields in curved spacetime. Perturbation theory is also explained. We
conclude with a discussion on the problem of backreaction of quantum fields in
spacetime geometry.Comment: 30 pages, latex; minor changes, added some explanations and refeence
Stochastic semiclassical gravity
In the first part of this paper, we show that the semiclassical
Einstein-Langevin equation, introduced in the framework of a stochastic
generalization of semiclassical gravity to describe the back reaction of matter
stress-energy fluctuations, can be formally derived from a functional method
based on the influence functional of Feynman and Vernon. In the second part, we
derive a number of results for background solutions of semiclassical gravity
consisting of stationary and conformally stationary spacetimes and scalar
fields in thermal equilibrium states. For these cases, fluctuation-dissipation
relations are derived. We also show that particle creation is related to the
vacuum stress-energy fluctuations and that it is enhanced by the presence of
stochastic metric fluctuations.Comment: 26 pages, RevTeX, no figure
Monte Carlo studies of the ordering of the one-dimensional Heisenberg spin glass with long-range power-law interactions
The nature of the ordering of the one-dimensional Heisenberg spin-glass model
with a long-range power-law interaction is studied by extensive Monte Carlo
simulations, with particular attention to the issue of the spin-chirality
decoupling/coupling. Large system sizes up to are studied. With
varying the exponent describing the power-law interaction, we observe
three distinct types of ordering regimes. For smaller , the spin and
the chirality order at a common finite temperature with a common
correlation-length exponent, exhibiting the standard spin-chirality coupling
behavior. For intermediate , the chirality orders at a temperature
higher than the spin, exhibiting the spin-chirality decoupling behavior. For
larger , both the spin and the chirality order at zero temperature. We
construct a phase diagram in the versus the temperature plane, and
discuss implications of the results. Critical properties associated with both
the chiral-glass and the spin-glass transitions are also determined.Comment: 28 pages, 26 figures, to appear in J. Phys. Soc. Jp
On the Neutral Scalar Sector of the General R-parity Violating MSSM
Starting out from the most general, gauge invariant and renormalizable scalar
potential of the R-parity violating MSSM and performing a calculable rotation
to the scalar fields we arrive at a basis where the sneutrino VEVs are zero.
The advantage of our rotation is that, in addition, we obtain diagonal soft
supersymmetry breaking sneutrino masses and all potential parameters and VEVs
real, proving that the MSSM scalar potential does not exhibit spontaneous or
explicit CP-violation at tree level. The model has five CP-even and four CP-odd
physical neutral scalars, with at least one CP-even scalar lighter than M_Z. We
parametrise the neutral scalar sector in a way that resembles the
parametrisation of the R-parity conserving MSSM, analyze its mass spectrum, the
coupling to the gauge sector and the stability of the potential.Comment: 19 pages, minor changes, published version to appear in PL
Ownership and control in a competitive industry
We study a differentiated product market in which an investor initially owns a controlling stake in one of two competing firms and may acquire a non-controlling or a controlling stake in a competitor, either directly using her own assets, or indirectly via the controlled firm. While industry profits are maximized within a symmetric two product monopoly, the investor attains this only in exceptional cases. Instead, she sometimes acquires a noncontrolling stake. Or she invests asymmetrically rather than pursuing a full takeover if she acquires a controlling one. Generally, she invests indirectly if she only wants to affect the product market outcome, and directly if acquiring shares is profitable per se. --differentiated products,separation of ownership and control,private benefits of control
Non-equilibrium dynamics of a thermal plasma in a gravitational field
We introduce functional methods to study the non-equilibrium dynamics of a
quantum massless scalar field at finite temperature in a gravitational field.
We calculate the Close Time Path (CTP) effective action and, using its formal
equivalence with the influence functional, derive the noise and dissipation
kernels of the quantum open system in terms of quantities in thermodynamical
equilibrium. Using this fact, we formally prove the existence of a
Fluctuation-Dissipation Relation (FDR) at all temperatures between the quantum
fluctuations of the plasma in thermal equilibrium and the energy dissipated by
the external gravitational field. What is new is the identification of a
stochastic source (noise) term arising from the quantum and thermal
fluctuations in the plasma field, and the derivation of a Langevin-type
equation which describes the non-equilibrium dynamics of the gravitational
field influenced by the plasma. The back reaction of the plasma on the
gravitational field is embodied in the FDR. From the CTP effective action the
contribution of the quantum scalar field to the thermal graviton polarization
tensor can also be derived and it is shown to agree with other techniques, most
notably, Linear Response Theory (LRT). We show the connection between the LRT,
which is applicable for near-equilibrium conditions and the functional methods
used in this work which are useful for fully non-equilibrium conditions.Comment: Final version published in Phys. Rev.
Mutations in pericentrin cause Seckel syndrome with defective ATR-dependent DNA damage signaling
Large brain size is one of the defining characteristics of modern humans. Seckel syndrome (MIM 210600), a disorder of markedly reduced brain and body size, is associated with defective ATR-dependent DNA damage signaling. Only a single hypomorphic mutation of ATR has been identified in this genetically heterogeneous condition. We now report that mutations in the gene encoding pericentrin (PCNT)--resulting in the loss of pericentrin from the centrosome, where it has key functions anchoring both structural and regulatory proteins--also cause Seckel syndrome. Furthermore, we find that cells of individuals with Seckel syndrome due to mutations in PCNT (PCNT-Seckel) have defects in ATR-dependent checkpoint signaling, providing the first evidence linking a structural centrosomal protein with DNA damage signaling. These findings also suggest that other known microcephaly genes implicated in either DNA repair responses or centrosomal function may act in common developmental pathways determining human brain and body size
Privatization and State Capacity in Postcommunist Society
Economists have used cross-national regression analysis to argue that postcommunist economic failure is the result of inadequate adherence liberal economic policies. Sociologists have relied on case study data to show that postcommunist economic failure is the outcome of too close adherence to liberal policy recommendations, which has led to an erosion of state effectiveness, and thus produced poor economic performance. The present paper advances a version of this statist theory based on a quantitative analysis of mass privatization programs in the postcommunist world. We argue that rapid large-scale privatization creates severe supply and demand shocks for enterprises, thereby inducing firm failure. The resulting erosion of tax revenues leads to a fiscal crisis for the state, and severely weakens its capacity and bureaucratic character. This, in turn, reacts back on the enterprise sector, as the state can no longer support the institutions necessary for the effective functioning of a modern economy, thus resulting in deindustrialization. Using cross-national regression techniques we find that the implementation of mass privatization programs negatively impacts measures of economic growth, state capacity and the security of property rights.http://deepblue.lib.umich.edu/bitstream/2027.42/40192/3/wp806.pd
Stochastic Gravity: A Primer with Applications
Stochastic semiclassical gravity of the 90's is a theory naturally evolved
from semiclassical gravity of the 70's and 80's. It improves on the
semiclassical Einstein equation with source given by the expectation value of
the stress-energy tensor of quantum matter fields in curved spacetimes by
incorporating an additional source due to their fluctuations. In stochastic
semiclassical gravity the main object of interest is the noise kernel, the
vacuum expectation value of the (operator-valued) stress-energy bi-tensor, and
the centerpiece is the (stochastic) Einstein-Langevin equation. We describe
this new theory via two approaches: the axiomatic and the functional. The
axiomatic approach is useful to see the structure of the theory from the
framework of semiclassical gravity. The functional approach uses the
Feynman-Vernon influence functional and the Schwinger-Keldysh close-time-path
effective action methods which are convenient for computations. It also brings
out the open systems concepts and the statistical and stochastic contents of
the theory such as dissipation, fluctuations, noise and decoherence. We then
describe the application of stochastic gravity to the backreaction problems in
cosmology and black hole physics. Intended as a first introduction to this
subject, this article places more emphasis on pedagogy than completeness.Comment: 46 pages Latex. Intended as a review in {\it Classical and Quantum
Gravity
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