117887312
Influence of momentum dependent interactions on nuclear stopping in symmetric heavy-ion collisions
The role of momentum dependent interactions is studied in nuclear stopping at intermediate energy using an isospin-dependent quantum molecular dynamics model. Present calculations are performed at incident energy between 50 and 1000 MeV/nucleon. Our findings show that nuclear stopping is sensitive towards the impact parameter, incident energies as well as towards the mass of the colliding system. Further, the degree of stopping is suppressed by the inclusion of momentum dependent interactions, whereas the particle production is not affected by the MDI.
117335698
Effect of isospin dependent cross-section on nuclear stopping
Nuclear stopping in heavy ion collisions (HIC) has been studied by means of rapidity distribution and asymmetry of nucleon momentum distribution. It is an important quantity in determining the outcome of a reaction. Fen Fu {\it et al.,} \cite{2} calculate both the radial flow and the degree of nuclear stopping in Pb + Pb and Ni + Ni at 0.4, 0.8 and 1.2 GeV/neucleon. They found that the expansion velocity as well as the degree of nuclear stopping are higher in the heavier system at all energies.
119288476
Influence of charge asymmetry and isospin dependent cross-section on nuclear stopping
Using the isospin dependent quantum molecular dynamics model, we study the effect of charge asymmetry and isospin dependent cross-section on nuclear stopping and multiplicity of free nucleons and LMF’s. Simulations were carried out for the reactions 124 Xm + 124 Xm, where m varies from 47 to 59 and for 40 Yn+ 40 Yn, where n varies from 14 to 23. Our study shows that nuclear stopping as well as the production of LMF’s depend strongly on the isospin of the cross-section.
118406564
Effect of the symmetry energy on nuclear stopping and its relation to the production of light charged fragments
We present a complete systematics (excitation function, impact parameter, system size, isospin asymmetry, and equations of state dependences) of global stopping and fragment production for heavy-ion reactions in the energy range between 50 and 1000 MeV/nucleon in the presence of symmetry energy and an isospin-dependent cross section. It is observed that the degree of stopping depends weakly on the symmetry energy and strongly on the isospin-dependent cross section. However, the symmetry energy and isospin-dependent cross section has an effect of the order of more than 10% on the emission of light charged particles (LCP's). It means that nuclear stopping and LCP's can be used as a tool to get the information of an isospin-dependent cross section. Interestingly, the LCP's emission in the presence of symmetry energy is found to be highly correlated with the global stopping.
118085314
Rapidity distribution dependence of the transition energy in heavy-ion collisions
For the present analysis, simulations are carried out for thousand of events for the reaction of 79Au197 + 79Au197 at semi-central geometry using a hard equation of state. The whole of the analysis is performed for light charged particles (LCP's). The transition from in-plane to out-of-plane is observed only when the mid-rapidity region is included in the rapidity bin otherwise no transition is observed. The transition energy is found to be strongly dependent on the size of the rapidity bin. The transition energy is parameterized with a straight line interpolation.
116891254
Production of light and intermediate mass fragments using various clusterization algorithms
For the present analysis we simulate the reaction 129Xe 54+197Au79 at E=50 MeV/nucleon respectively[3]. This reaction is simulated at different impact parameters using hard equation of state. The stored phase space is then analyzed by using MST, MSTP and MSTB algorithms. MSTB and MSTP identifies the free nucleons as early as possible. In the two cases, a check in the form of binding energy and momentum cut helps to identify the fragments quite early. The normal MST takes quite a long time to identify the stable fragments which are residual of excited fragments.
15129104
Self-Consistent Dynamics of Inflationary Phase Transitions
The physics of the inflationary universe requires the study of the out of equilibrium evolution of quantum fields in curved spacetime. We present the evolution for both the geometry and the matter (described by the quantum inflaton field) by means of the non-perturbative large N limit combined with semi-classical gravitational dynamics including the back-reaction of quantum fluctuations self-consistently for a new inflation scenario. We provide a criterion for the validity of the classical approximation and a full analysis of the case in which spinodal quantum fluctuations drive the evolution of the scale factor. Under carefully determined conditions, we show that the full field equations may be well approximated by those of a single composite field which obeys the classical equation of motion in all cases. The de Sitter stage is found to be followed by a matter dominated phase. We compute the spectrum of scalar density perturbations and argue that the spinodal instabilities are responsible for a `red' spectrum with more power at longer wavelengths. A criterion for the validity of these models is provided and contact with the reconstruction program is established.
15230645
Critical generation of soliton mode in a gauged O(3) sigma model with interpolating potential
We show that a new soliton mode is generated in a gauged sigma model with interpolating potential when the interpolation parameter decreases below a critical value. pradip@boson.bose.res.in kumar@boson.bose.res.in Recently a class of gauged O(3) sigma models in three dimensions have been studied [1, 2, 3, 4, 5] where a U(1) subgroup of the O(3) symmetry of the model was gauged by coupling the sigma model fields with a gauge field through the corresponding U(1) current. This is different from the minimal coupling via the topological current discussed previously [6]. The motivation behind the new gauged O(3) sigma models was to break the scale invariance of the self dual solutions of the usual O(3) sigma model [7]. Initially the gauge field dynamics was assumed to be dictated by the Maxwell term [1]. Later the extension of the model with the Chern Simons coupling was investigated [2]. A particular form of self interaction was required to be included in these models in order to saturate the Bogomol’nyi bounds [8]. The form of the assumed self interaction potential is of crucial importance. The minima of the potential determine the vaccum structure of the theory. The solutions change remarkably when the vaccum structure exhibits spontaneous breaking of the symmetry of the gauge group. Thus it was demonstrated that the observed degeneracy of the solutions of [1, 2] is lifted when potentials with symmetry breaking minima were incorporated [4, 5]. A generalisation of the models [1, 2] was proposed in [3]where an adjustable real parameter v was introduced in the expression of the self interaction potential. Detailed solutions of the model with the C S coupling were provided. The parameter v interpolates between the symmetric and symmetry breaking phases. The inclusion of such adjustable potential in the corresponding Maxwell coupled model was conjectured, but not fully explored. In this letter we show that this generalisation indeed leads to certain important consequences. The most interesting outcome is a kind of ’critical phenomenon’ where a new self dual soliton mode emerges when the parameter v decreases below v = 1. It will be useful to start with a brief review of the nonlinear O(3) sigma model [7]. The lagrangian of the model is given by, L = 1 2 ∂μφ · ∂ φ (1) Here φ is a triplet of scalar fields constituting a vector in the internal space with unit norm φa = na · φ, (a = 1, 2, 3) (2) φ · φ = φaφa = 1 (3) The vectors na constitute a basis of unit orthogonal vectors in the internal space. We work in the Minkowskian space time with the metric tensor diagonal, gμν = (1,−1,−1). The finite energy solutions of the model (1) satisfies the boundary condition limφ = φa(0) (4) at physiacal infinity. The condition (4) corresponds to one point compactification of the physical infinity. The physical space R2 becomes topologically equivalent to S2 due to this compactification. The static finite energy solutions of the model are then maps from this sphere to the internal sphere. Such solutions are classified by the homotopy [9]
122529836
Anisotropic dark energy models with constant deceleration parameter
We consider a spatially homogeneous and totally anisotropic Bianchi-I space-time with perfect fluid (dark matter and standard visible matter) and anisotropic dark energy, which has dynamical energy density. The two sources are assumed to interact minimally and therefore their energy momentum tensors are conserved separately. Using suitable physical assumptions, the field equations are solved exactly. Various dark energy models are studied and it is found that quintessence model is suitable for describing the present evolution of the universe. The geometrical and kinematical features of the models and the behavior of the anisotropy of the dark energy, are examined in detail.
14630427
Spectral distortions at super-kamiokande
We examine the effect of the rise in the survival probability of the electron neutrinos with the decrease in the neutrino energy on the recoil electron spectrum at Super-Kamiokande.
116887728
Sensitivity of elliptical flow in intermediate energy heavy-ion collisions
The detailed analysis of excitation function of elliptical flow by taking into account the nature of equation of state, nucleon-nucleon cross sections as well as momentum dependent interactions is performed within Quantum Molecular Dynamics (QMD)model. All the observables are found to sensitive towards the elliptical flow. The transition energy is found to be decrease with increase in the size of the fragment in the presence of static equation of state as well as with large cross sections, while, trend gets opposite when momentum dependent interactions are included. At last, the experimental data is verified with static hard equation of state in the presence of large cross sections.