6716809
Performance of an Axial Gas Ionization Detector
An axial gas ionization chamber has been fabricated for use as a DeltaE detector in heavy ion induced nuclear reactions. Different operating parameters such as gas type, pressure, anode voltage, and anode structures have been optimized. The transparency of the anode structure is observed to play an important role in improving the energy resolution of the detector
121131613
Effect of higher order couplings in the barrier distribution of 12 C + 142 Nd extracted from quasielastic excitation functions
To explore the effects of higher order coupling on the barrier distribution, we have measured the quasielastic excitation function for 12 C+ 142 Nd around the nominal Coulomb barrier from 44 to 58 MeV in steps of 1 MeV. Theoretical coupled channel calculations with one and two phonon states were performed using the code ECIS94. The analysis showed that the second order coupling effects explained the barrier distribution profile and excitation function more appropriately than the first order couplings.
119115082
Quantum quench across a zero temperature holographic superfluid transition
A bstractWe study quantum quench in a holographic model of a zero temperature insulator-superfluid transition. The model is a modification of that of arXiv:0911.0962 and involves a self-coupled complex scalar field, Einstein gravity with a negative cosmological constant, and Maxwell field with one of the spatial directions compact. In a suitable regime of parameters, the scalar field can be treated as a probe field whose backreaction to both the metric and the gauge field can be ignored. We show that when the chemical potential of the dual field theory lies between two critical values, the equilibrium background geometry is an AdS soliton with a constant gauge field, while the complex scalar condenses leading to broken symmetry. We then turn on a time dependent source for the order parameter which interpolates between constant values and crosses the order-disorder critical point. In the critical region adiabaticity breaks down, but for a small rate of change of the source v there is a new small-v expansion in fractional powers of v. The resulting critical dynamics is dominated by a zero mode of the bulk field. To lowest order in this small-v expansion, the order parameter satisfies a time dependent Landau-Ginsburg equation which has z = 2, but non-dissipative. These predictions are verified by explicit numerical solutions of the bulk equations of motion.
118390596
Quantum quench and double trace couplings
A bstractWe consider quantum quench by a time dependent double trace coupling in a strongly coupled large N field theory which has a gravity dual via the AdS/CFT correspondence. The bulk theory contains a self coupled neutral scalar field coupled to gravity with negative cosmological constant. We study the scalar dynamics in the probe approximation in two backgrounds: AdS soliton and AdS black brane. In either case we find that in equilibrium there is a critical phase transition at a negative value of the double trace coupling κ below which the scalar condenses. For a slowly varying homogeneous time dependent coupling crossing the critical point, we show that the dynamics in the critical region is dominated by a single mode of the bulk field. This mode satisfies a Landau-Ginsburg equation with a time dependent mass, and leads to Kibble Zurek type scaling behavior. For the AdS soliton the system is non-dissipative and has z = 1, while for the black brane one has dissipative z = 2 dynamics. We also discuss the features of a holographic model which would describe the non-equilibrium dynamics around quantum critical points with arbitrary dynamical critical exponent z and correlation length exponent ν. These analytical results are supported by direct numerical solutions.
118683100
Supercurrent: Vector hair for an AdS black hole
Hartnoll, Herzog, and Horowitz [Phys. Rev. Lett. 101, 031601 (2008).] discuss a holographic black hole solution which exhibits a superconductorlike transition. In the superconducting phase the black holes show infinite DC conductivity. This gives rise to the possibility of deforming the solutions by turning on a time independent current (supercurrent), without any electric field. This type of deformation does not exist for normal (nonsuperconducting) black holes, due to the no-hair theorems. In this paper we have studied such a supercurrent solution and the associated phase diagram. Interestingly, we have found a 'special point' (critical point) in the phase diagram where the second order superconducting phase transition becomes first order. Supercurrent in superconducting materials is a well studied phenomenon in condensed matter systems. We have found some qualitative agreement with known results.