17830761
Correlation entropy of an interacting quantum field and H theorem for the O(N) model
Following the paradigm of Boltzmann-BBGKY we propose a correlation entropy (of the nth order) for an interacting quantum field, obtained by `slaving' (truncation with causal factorization) of the higher (n+1 th) order correlation functions in the Schwinger-Dyson system of equations. This renders an otherwise closed system effectively open where dissipation arises. The concept of correlation entropy is useful for addressing issues related to thermalization. As a small yet important step in that direction we prove an H-theorem for the correlation entropy of a quantum mechanical O(N) model with a Closed Time Path Two Particle Irreducible Effective Action at the level of Next-to-Leading-Order large N approximation. This model may be regarded as a field theory in $0$ space dimensions.
118352317
GRAVITY AND NONEQUILIBRIUM THERMODYNAMICS OF CLASSICAL MATTER
Happy Birthday Mario, the philosopher, the king and the philosopher king! — This was explained in the first few slides of my talk at Mariofest. In an earlier, different occasion I had compared Mario, in his capacity of an inspiring mentor and a chief architect, in building up an eminent school of theoretical physics and astrophysics in Argentina, to my own Ph.D. advisor, the late Professor John Archibald Wheeler, in the USA. The nature of this meeting could perhaps allow me to also relate some of my past experience with Wheeler, and to pay homage to his influence on me in the same capacity as is done here by many young researchers, leaders in their own rights in different fields of physics and astrophysics, with Mario. So please forgive me if you find me delving at times into the past, referring to what I was thinking when I was a graduate student, some 40 years ago, on certain topics, some still of current interest. One of these ideas bears on the present theme of gravity in relation to thermodynamics, another on the philosophy I use for understanding it.
22366791
Noise kernel in stochastic gravity and stress energy bitensor 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.
18511662
Noise and fluctuations in semiclassical gravity.
We continue our earlier investigation of the back reaction problem in semiclassical gravity with the Schwinger-Keldysh or closed-time-path (CTP) functional formalism using the language of the decoherent history formulation of quantum mechanics. Making use of its intimate relation with the Feynman-Vernon influence functional method, we examine the statistical mechanical meaning and show the interrelation of the many quantum processes involved in the back reaction problem, such as particle creation, decoherence, and dissipation. We show how noise and fluctuation arise naturally from the CTP formalism. We derive an expression for the CTP effective action in terms of the Bogoliubov coefficients and show how noise is related to the fluctuations in the number of particles created. In so doing we have extended the old framework of semiclassical gravity, based on the mean field theory of Einstein equation with a source given by the expectation value of the energy-momentum tensor, to that based on a Langevin-type equation, where the dynamics of the fluctuations of spacetime is driven by the quantum fluctuations of the matter field. This generalized framework is useful for the investigation of quantum processes in the early Universe involving fluctuations, vacuum instability, and phase transition phenomena as well as the nonequilibrium thermodynamics of black holes. It is also essential to an understanding of the transition from any quantum theory of gravity to classical general relativity.
118267306
Cosmology as `Condensed Matter' Physics
We note that in general there exist two basic aspects in any branch of physics, including cosmology - one dealing with the attributes of basic constituents and forces of nature, the other dealing with how structures arise from them and how they evolve. Current research in quantum and superstring cosmology is directed mainly towards the first aspect, even though a viable theory of the underlying interactions is lacking. We call the attention to the development of the second aspect, i.e., on the organization and processing of the basic constituents of matter (in classical cosmology) and spacetime (in quantum cosmology). Many newly developed concepts and techniques in condensed matter physics stemming from the investigation of disordered, dynamical and complex systems can guide us in asking the right questions and formulating new solutions to existing and developing cosmological issues, thereby broadening our view of the universe both in its formative and present state.
204002791
Phase transitions in the early universe: geometric effects.
121822978
The classical Ising model: A quantum renormalization group approach☆
Abstract Proceeding from the equivalence between the d -dimentional classical Ising model and the ( d −1)-dimentional quantum mechanical Ising model in a transverse magnetic field, we study the critical properties of the classical model via the quantum mechanical model. Quantum renormalization group transformations based on the truncation method and the ground state projection operator method are used to calculate the critical exponents. They are found to agree well with the “exact” values.
123516619
Nonanalytic twist maps and Frenkel-Kontorova models
We give a review of our recent works on a class of twist maps and Frenkel-Kontorova (FK) models in which the external potential function is nonanalytic (C1) and endowed with a variable degree of inflection z. When z > 3, recurrence of invariant curves has been observed. An “inverse residue criterion” for the reappearance of an invariant curve — complementary to the “residue criterion” for the disappearance of an invariant curve — is introduced to make a precise determination of the reappearance point. We have also studied the local and global scaling behaviors of these curves. The critical exponents, the singularity spectrum, and the generalized dimensions are found to vary with z when 2 ⩽ z < 3, but remain the same for z ⩾ 3. The degree of inflection thus plays a role reminiscent of that of dimensionality in phase transitions with z = 2 and 3 corresponding respectively to the lower and upper critical dimensions. When the same nonanalytic function is substituted for the sinusoidal external potential in the standard FK model, the same conclusions are reached: there exists a sequence of pinning-depinning transitions, and the critical exponents of the phonon gap, the coherence length, and the Peierls-Nabarro barrier all show the same dependence on z.
123178585
Tricriticality of the renormalization-group-generated BEG model
Abstract By virtue of the transfer matrix the classical spin-1 Ising model is transformed into a quantum spin-1 model in a transverse field. However, when the truncation renormalization group is applied to this quantum-mechanical model, new terms are generated. The resultant model that is closed under renormalization is the quantum version of the Blume-Emery-Griffiths (BEG) model. The tricritical exponents are calculated, and they are found to agree well with the values obtained from previous classical renormalization group studies.
123110822
Corrections to scaling for period doubling
We have studied a multiple scaling which describes corrections to scaling. For the period doubling in one-dimensional dissipative maps, two-dimensional areapreserving maps, and four-dimensional symplectic maps, the multiple scaling is seen to be well-obeyed, and new scaling factors have been found. The multiple scaling is also seen to be a very powerful tool for searching for scaling behavior.
120083683
Density measurement through elastic electron scattering with a gaseous target at the Jefferson Lab
We report the density measurement through e-^(3)He elastic scattering with a 1.23 GeV electron beam in Jefferson Lab experiment E06-010. The extracted 3He density is (9.26±0.06) amagats and the N_(2)/^(3)He ratio is (1.49±0.08)%. In addition, these results are consistent with the deduced target densities based on pressure broadening measurement.