16386311
Photoproduction enhancement from nonequilibrium disoriented chiral condensates
We study photoproduction during the non-equilibrium stages of the formation of chiral condensates within the ``quench'' scenario of the chiral phase transition. The dynamics is modeled with a gauged linear sigma model. A novel quantum kinetic approach to the description of photoproduction far off equilibrium is developed. We find that non-equilibrium spinodal instabilities of long wavelength pion fluctuations are responsible for an enhanced photoproduction rate for energies $\leq 80$ MeV at order $\alpha$. These non-equilibrium effects lead to a larger contribution than the typical processes in the medium, including that of the anomalous neutral pion decay $\pi^0 \rightarrow 2 \gamma$ (which is of order $\alpha^2$). We follow the evolution of the dynamics throughout the phase transition, which in this scenario occurs on a time scale of about $2.5-3$ fm/c and integrate the photon yield through its evolution. The spectrum of photons produced throughout the phase transition is a non- equilibrium one. For thermal initial conditions at the time of the quench it interpolates between a thermal distribution about 6% above the initial temperature (at the time of the quench) for low energy $\leq 80$ MeV photons, and a high energy tail in thermal equilibrium at the initial temperature, with a smooth crossover at 100 MeV. The rate displays a peak at $\sim 35$ MeV which receives a larger enhancement the closer the initial temperature at the time of the quench is to the critical temperature. It is found that the enhancement of photoproduction at low energies is not an artifact caused by the initial distribution of the photons, but is due to the pionic instabilities. We suggest that these strong out of equilibrium effects may provide experimental signatures for the formation and relaxation of DCC's in heavy ion collisions.
5243610
Non-Abelian Vortices at Weak and Strong Coupling in Mass Deformed ABJM Theory
We find half-BPS vortex solitons, at both weak and strong coupling, in the = 6 supersymmetric mass deformation of ABJM theory with U(N) × U(N) gauge symmetry and Chern-Simons level k. The strong coupling gravity dual is obtained by performing a k quotient of the = 8 supersymmetric eleven dimensional supergravity background of Lin, Lunin and Maldacena corresponding to the mass deformed M2-brane theory. At weak coupling, the BPS vortices preserving six supersymmetries are found in the Higgs vacuum of the theory where the gauge symmetry is broken to U(1) × U(1). The classical vortex solitons break a colour-flavour locked global symmetry resulting in non-Abelian internal orientational moduli and a CP1 moduli space of solutions. At strong coupling and large k, upon reduction to type IIA strings, the vortex moduli space and its action are computed by a probe D0-brane in the dual geometry. The mass of the D0-brane matches the classical vortex mass. However, the gravity picture exhibits a six dimensional moduli space of solutions, a section of which can be identified as the CP1 we find classically, along with a Dirac monopole connection of strength k. It is likely that the extra four dimensions in the moduli space are an artifact of the strong coupling limit and of the supergravity approximation.
59440238
Vacuum structure and flavor symmetry breaking in supersymmetric SO(nc) gauge theories
We determine the vacuum structure and phases of N=1 theories obtained via a 
mass \mu for the adjoint chiral superfield in N=2, SO(n_c) SQCD. For large 
number of flavors these theories have two groups of vacua. The first exhibits 
dynamical breaking of flavor symmetry \USp(2n_f) \to U(n_f) and arises as a 
relevant deformation of a non-trivial superconformal theory. These are in the 
confined phase. The second group, in an IR-free phase with unbroken flavor 
symmetry, is produced from a Coulomb branch singularity with Seiberg's dual 
gauge symmetry. In the large-\mu regime both groups of vacua are well-described 
by dual quarks and mesons, and dynamical symmetry breaking in the first group 
occurs via meson condensation. We follow the description of these vacua from 
weak to strong coupling and demonstrate a nontrivial agreement between the 
phases and the number of vacua in the two regimes. We construct the 
semiclassical monopole flavor multiplets and argue that their multiplicity is 
consistent with the number of N=1 vacua.
17544914
Precision test of AdS/CFT in Lunin-Maldacena background
We obtain the solutions and explicitly calculate the energy for a class of two-spin semiclassical string states in the Lunin-Maldacena background. These configurations are the β-deformed versions of the folded string solutions in AdS5 × S5 background. They correspond to certain single trace operators in the = 1 superconformal β deformation of = 4 Yang-Mills. We calculate the one loop anomalous dimension for the dual single trace operators from the associated twisted spin chain with a general two-cut distribution of Bethe roots. Our results show a striking match between the two calculations. We demonstrate the natural identification of parameters on the two sides of the analysis, and explain the significance of the Virasoro constraint associated with the winding motion of semiclassical strings from the perspective of the spin chain solution.
18863456
Out of Equilibrium Fields in Inflationary Dynamics. Density Fluctuations
The energy and time scales during the inflationary stage of the universe calls for an out of equilibrium quantum field treatment. Moreover, the high energy densities involved (∼1/g ∼ 1012) make necessary the use of non-perturbative approaches as the large N and Hartree methods. We start these lectures by introducing the such non-perturbative out of equilibrium methods in cosmological universes. We discuss the renormalization procedure and the choice of initial conditions. We then study with these methods the non-linear dynamics of quantum fields in matter and radiation dominated FRW and de Sitter universes. For a variety of initial conditions, we compute the evolution of the inflaton, its quantum fluctuations and the equation of state. We investigate the phenomenon of explosive particle production due to spinodal instabilities and parametric amplification in FRW and de Sitter universes with and without symmetry breaking. We find that the particle production is somewhat sensitive to the expansion of the universe. In the large N limit for symmetry breaking scenarios, we determine generic late time fields behavior for any flat FRW and de Sitter cosmology. We find that quantum fluctuations damp in FRW as the square of the scale factor while the order parameter approaches a minimum of the potential at the same rate. We present a complete and numerically accessible renormalization scheme for the equation of motion and the energy momentum tensor in flat cosmologies. In this scheme the renormalization constants are independent of time and of the initial conditions. Furthermore, we consider an O(N) inflaton model coupled self-consistently to gravity in the semiclassical approximation, where the field is subject to ‘new inflation’ type initial conditions. We study the dynamics self-consistently and non-perturbatively with non-equilibrium field theory methods in the large N limit. We find that spinodal instabilities drive the growth of non-perturbatively large quantum fluctuations which shut off the inflationary growth of the scale factor. We find that a very specific combination of these large fluctuations plus the inflaton zero mode assemble into a new effective field. This new field behaves classically and it is the object which actually rolls down. We show how this reinterpretation qualitatively saves the standard picture of how metric perturbations are generated during inflation and that the spinodal growth of fluctuations dominates the time dependence of the Bardeen variable for superhorizon modes during inflation. We compute the amplitude and index for the spectrum of scalar density and tensor perturbations and argue that in all models of this type the spinodal instabilities are responsible for a ‘red’ spectrum of primordial scalar density perturbations. The decoherence aspects and the quantum to classical transition through inflation are studied in detail by following the full evolution of the density matrix.
15505916
Exact Superpotentials from Matrix Models
Dijkgraaf and Vafa (DV) have conjectured that the exact superpotential for a large class of = 1 SUSY gauge theories can be extracted from the planar limit of a certain holomorphic matrix integral. We test their proposal against existing knowledge for a family of deformations of = 4 SUSY Yang-Mills theory involving an arbitrary polynomial superpotential for one of the three adjoint chiral superfields. Specifically, we compare the DV prediction for these models with earlier results based on the connection between SUSY gauge theories and integrable systems. We find complete agreement between the two approaches. In particular we show how the DV proposal allows the extraction of the exact eigenvalues of the adjoint scalar in the confining vacuum and hence computes all related condensates of the finite-N gauge theory. We extend these results to include Leigh-Strassler deformations of the = 4 theory.
118221659
Role of Momentum Dependent Interactions in Nuclear Stopping
In the present analysis, thousand of events were simulated for the neutron rich reaction of 54Xe131 + 54Xe131, at different impact parameters using hard (HMD) and soft (SMD) momentum dependent equation of state. one can clearly see more stopping in the presence of HMD. Production of LCP's and free particles follows the same trend as stopping parameter R. This simply implies that the fragment production can act as a global indicator for the nuclear stopping.
119276827
Observational constraints on Hubble constant and deceleration parameter in power-law cosmology
In this paper, we show that the expansion history of the Universe in power-law cosmology essentially depends on two crucial parameters, namely the Hubble constant $H_{0}$ and deceleration parameter $q$. We find the constraints on these parameters from the latest $H(z)$ and SNe Ia data. At 1$\sigma$ level the constraints from $H(z)$ data are obtained as $q=-0.18_{-0.12}^{+0.12}$ and $H_{0}=68.43_{-2.80}^{+2.84}$ km s$^{-1}$ Mpc$^{-1}$ while the constraints from the SNe Ia data read as $q=-0.38_{-0.05}^{+0.05}$ and $H_{0}=69.18_{-0.54}^{+0.55}$ km s$^{-1}$ Mpc$^{-1}$. We also perform the joint test using $H(z)$ and SNe Ia data, which yields the constraints $q=-0.34_{-0.05}^{+0.05}$ and $H_{0}=68.93_{-0.52}^{+0.53}$ km s$^{-1}$ Mpc$^{-1}$. The estimates of $H_{0}$ are found to be in close agreement with some recent probes carried out in the literature. The analysis reveals that the observational data successfully describe the cosmic acceleration within the framework of power-law cosmology. We find that the power-law cosmology accommodates well the $H(z)$ and SNe Ia data. We also test the power-law cosmology using the primordial nucleosynthesis, which yields the constraints $q\gtrsim 0.72$ and $H_{0}\lesssim 41.49$ km s$^{-1}$ Mpc$^{-1}$. These constraints are found to be inconsistent with the ones derived from the $H(z)$ and SNe Ia data. We carry out the statefinder analysis, and find that the power-law cosmological models approach the standard $\Lambda$CDM model as $q\rightarrow -1$. Finally, we conclude that despite having several good features power-law cosmology is not a complete package for the cosmological purposes.
123016106
Different nucleon-nucleon cross sections and multifragmentation
We present a systematic study of the dependence of the fragment production on the nucleon-nucleon cross section using the quantum molecular dynamics model as an event generator. We employ constant energy-dependent and in-medium cross sections. In our analysis, fragments are formed using a minimum spanning tree description. The fragment distribution with different cross sections at low energy is nearly the same. At higher energies, different nucleon-nucleon (NN) cross sections have small effects on fragment production for central collisions, whereas the fragment production is strongly influenced at semicentral and peripheral collisions. A larger NN cross section results in more intermediate mass fragments at peripheral collisions with a shift of the peak towards larger impact parameters. As a result, the rapidity distribution of fragments and the fragment flow is also affected by the choice of the cross section. This influence is reduced if fragments are constructed with a sophisticated algorithm such as the simulated annealing clusterization algorithm which searches for the most bound configuration of nucleons and fragments.
118577769
Effect of density dependent symmetry energy on Elliptical flow
Nuclear Physics in general and heavy-ion collisions in particular is of central interest in investigating the matter under the extreme conditions of temperature and compression. Among the different observables, collective flow and its various forms enjoys a special status, due to its sensitivity towards model ingredients that define equation of state. The elliptical flow, which is the squeeze out of spectator matter out of the reaction plane, is more suited to study the collective flow,, as compared to the directed flow, which is constrained only along the reaction plane.
119234278
Rapidity distribution as a probe for elliptical flow at intermediate energies
The interplay between spectator and participant matter in heavy-ion collisions is investigated within the isospin-dependent quantum molecular dynamics (IQMD) model in terms of the rapidity distribution of light charged particles. The effect of different types and sizes of rapidity distributions is studied in elliptical flow. The elliptical-flow patterns show the important role of nearby spectator matter on the participant zone. This role is further explained on the basis of the passing time of the spectator and the expansion time of the participant zone. The transition from in-plane to out-of-plane emission is observed only when the mid-rapidity region is included into the rapidity bin. Otherwise no transition occurs. The transition energy is found to be highly sensitive to the size of the rapidity bin, while it is only weakly dependent on the type of the rapidity distribution. These theoretical findings are found to be in agreement with experimental results.