118743898
On holographic thermalization and gravitational collapse of tachyonic scalar fields
A bstractIn this paper we study the thermalization of a spatially homogeneous system in a strongly coupled CFT. The non-equilibrium initial state is created by switching on a relevant perturbation in the CFT vacuum during Δt ≳ t ≳ − Δt. Via AdS/CFT, the thermalization process corresponds to the gravitational collapse of a tachyonic scalar field (m2 = −3) in the Poincare patch of AdS5. In the limit $ \varDelta t<\frac{0.02 }{T} $, the thermalization time tT is found to be quantitatively the same as that of a non-equilibrium state created by a marginal perturbation discussed in ref. [5]. In the case $ \varDelta t\gtrsim \frac{1}{T} $ we also obtain double- collapse solutions but with a non-equilibrium intermediate state at t = 0. In all the cases our results show that the system thermalizes in a typical time $ {t_T}\simeq \frac{O(1) }{T} $. Besides, a conserved energy-moment current in the bulk is found, which helps understand the qualitative difference of the collapse process in the Poincare patch from that in global AdS [10, 11].
118447664
Nonrenormalizability of the classical statistical approximation
In this paper, we discuss questions related to the renormalizability of the classical statistical approximation, an approximation scheme that has been used recently in several studies of out-of-equilibrium problems in Quantum Field Theory. Although the ultraviolet power counting in this approximation scheme is identical to that of the unapproximated quantum field theory, this approximation is not renormalizable. The leading cause of this non-renormalizability is the breakdown of Weinberg's theorem in this approximation. We also discuss some practical implications of this negative result for simulations that employ this approximation scheme, and we speculate about a possible modification of the classical statistical approximation in order to systematically subtract the leading residual divergences.
119251781
Looking inside neutron stars: Microscopic calculations confront observations
While QCD appears not to be accurately solvable in the regime of interest for neutron star physics, microscopic calculations are feasible at both low and very high densities. In this work, we propose using the most realistic calculations in these two regimes of nuclear physics and perturbative QCD, and construct equations of state by matching the results requiring thermodynamic consistency. We find that the resulting equations of state --- in contrast to several hadronic ones --- are able to reproduce current observational data on neutron stars without any fine tuning, and allow stable hybrid stars with masses up to 2.1M_{sun}. Using recent observations of star radii, we perform a maximum likelihood analysis to further constrain the equation of state, and in addition show that the effects of rotation on radii and masses should not be neglected in future precision studies.
53531246
Lattice worldline representation of correlators in a background field
A bstractWe use a discrete worldline representation in order to study the continuum limit of the one-loop expectation value of dimension two and four local operators in a background field. We illustrate this technique in the case of a scalar field coupled to a non-Abelian background gauge field. The first two coefficients of the expansion in powers of the lattice spacing can be expressed as sums over random walks on a d-dimensional cubic lattice. Using combinatorial identities for the distribution of the areas of closed random walks on a lattice, these coefficients can be turned into simple integrals. Our results are valid for an anisotropic lattice, with arbitrary lattice spacings in each direction.
119212232
Quark production, Bose-Einstein condensates and thermalization of the quark-gluon plasma
Abstract In this paper, we study the thermalization of gluons and N f flavors of massless quarks and antiquarks in a spatially homogeneous system. First, two coupled transport equations for gluons and quarks (and antiquarks) are derived within the diffusion approximation of the Boltzmann equation, with only 2 ↔ 2 processes included in the collision term. Then, these transport equations are solved numerically in order to study the thermalization of the quark–gluon plasma. At initial time, we assume that only gluons are present and we choose the gluon distribution of a form inspired by the color glass picture, namely f = f 0 θ ( 1 − p Q s ) with Q s the saturation momentum and f 0 a constant. The subsequent evolution of the system may, or may not, lead to the formation of a (transient) Bose condensate (BEC) of gluons, depending on the value of f 0 . In fact, we observe, depending on the value of f 0 , three different patterns: (a) thermalization without BEC for f 0 ≤ f 0 t , (b) thermalization with transient BEC for f 0 t f 0 ≤ f 0 c , and (c) thermalization with BEC for f 0 c f 0 . The values of f 0 t and f 0 c depend on N f . When f 0 ≳ 1 > f 0 c , the onset of BEC occurs at a finite time t c ∼ 1 ( α s f 0 ) 2 1 Q s . We also find that quark production slows down the thermalization process: the equilibration time for N f = 3 is typically about 5 to 6 times longer than that for N f = 0 at the same Q s and f 0 .
17627816
Exclusive vs. diffractive vector meson production in DIS at small x or off nuclei
The diffractive production of vector mesons in deep inelastic scattering (DIS) is calculated in the McLerran-Venugopalan model. This is relevant when large parton densities are probed by the virtual photon, as is the case at small Bjorken x or in DIS off nuclei. We investigate differences between the exclusive production (when the target doesn't break up) which dominates at small momentum transfer squared |t|, and the diffractive production (when the target scatters inelastically) which dominates at large |t|.
28663874
Modelling of the ALICE data acquisition system
The Heavy Ion Experiment ALICE is one of the three experiments at the LHC accelerator at CERN. Modeling and simulation of the large scale ALICE Data Acquisition (DAQ) system is necessary in order to study the behavior of the system. The development of a simulator -- ALSIM for the ALICE Data Acquisition System -- is described. ALSIM models front-end data readout, event building, data reduction and data storage. Technology dependent implementations can be linked in various topologies can be defined dynamically by means of description files. The simulation environment will be described as well as details of the model.
196069470
Reference Manual and User's Manual for ALICE DAQ Modelling and Simulation
196095135
Simulation of Central and Dimuon Events in the ALICE DAQ System.