119256345
The many phases of holographic superfluids
We investigate holographic superfluids in AdSd+1 with d =3, 4 in the nonbackreacted approximation for various masses of the scalar field. In d =3 the phase structure is universal for all the masses that we consider: the critical temperature decreases as the superfluid velocity increases, and as it is cranked high enough, the order of the phase transition changes from second to first. Surprisingly, in d = 4 we find that the phase structure is more intricate. For sufficiently high mass, there is always a second order phase transition to the normal phase, no matter how high the superfluid velocity. For some parameters, as we lower the temperature, this transition happens before a first order transition to a new super conducting phase. Across this first order transition, the gap in the transverse conductivity jumps from almost zero to about half its maximum value. We also introduce a double scaling limit where we can study the phase transitions(semi-)analytically in the large velocity limit. The results corroborate and complement our numerical results. In d =4, this approach has the virtue of being fully analytically tractable.
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.
119212250
Analytic approaches to anisotropic holographic superfluids
A bstractWe construct an analytic solution of the Einstein-SU(2)-Yang-Mills system as the holographic dual of an anisotropic superfluid near its critical point, up to leading corrections in both the inverse Yang-Mills coupling and a symmetry breaking order parameter. We have also calculated the ratio of shear viscosity to entropy density in this background, and shown that the universality of this ratio is lost in the broken symmetry direction. The ratio displays a scaling behavior near the critical point with critical exponent β = 1, at the leading order in the double expansion.
3995010
Superconductivity from D3/D7: holographic pion superfluid
We show that a D3/D7 system (in the limit of zero quark mass) at finite isospin chemical potential goes through a superconductor (superfluid) like phase transition. This is similar to a flavored superfluid phase studied in the QCD literature, where mesonic operators condense. We have studied the frequency dependent conductivity of the condensate and found a delta function peak in the zero frequency limit. This is an example of superconductivity in a string theory context. Consequently we have found a superfluid/supercurrent type solution and studied the associated phase diagram. The superconducting transition changes from second order to first order at a critical superfluid velocity. We have studied various properties of the superconducting system like superfluid density, energy gap, second sound etc. We investigate the possibility of the isospin chemical potential modifying the embedding of the flavor branes by checking whether the transverse scalars also condense at low temperatures. This however does not seem to be the case.
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.
118578316
Chaos around holographic Regge trajectories
A bstractUsing methods of Hamiltonian dynamical systems, we show analytically that a dynamical system connected to the classical spinning string solution holographically dual to the principal Regge trajectory is non-integrable. The Regge trajectories themselves form an integrable island in the total phase space of the dynamical system. Our argument applies to any gravity background dual to confining field theories and we verify it explicitly in various supergravity backgrounds: Klebanov-Strassler, Maldacena-Núñez, Witten QCD and the AdS soliton. Having established non-integrability for this general class of supergravity backgrounds, we show explicitly by direct computation of the Poincaré sections and the largest Lyapunov exponent, that such strings have chaotic motion.
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.
120752932
Elastic scattering and fusion cross sections for Be7,Li7+Al27 systems
Quasi-elastic-scattering and transfer reaction cross-section measurements were made for the {sup 7}Be+{sup 27}Al system at E{sub lab}=17, 19, and 21 MeV in the angular range {theta}{sub c.m.}=12 deg. An optical model (OM) analysis of the quasi-elastic scattering data was carried out. The fusion cross sections were derived at these energies by subtraction of the integrated transfer cross sections from the reaction cross sections obtained from the fits to quasi-elastic-scattering data. These fusion cross sections were found to be consistent with those obtained from the coupled-channels calculations. Elastic scattering and fusion cross sections were measured for the {sup 7}Li+{sup 27}Al system at E{sub lab}=10, 13, 16, 19, and 24 MeV. For elastic scattering the angular coverages were in the {theta}{sub lab}=12 deg. - 72 deg. range and for fusion the {alpha}-evaporation spectra from the compound nucleus were measured in the angular range {theta}{sub lab}=52 deg. - 132 deg. (142 deg. at 10 MeV). The elastic-scattering angular distributions were subjected to OM analysis. The {alpha}-evaporation spectra were reproduced with the statistical model calculations, and the fusion cross sections were extracted from them. The fusion cross sections were also extracted by subtraction of the integrated inelastic-scattering cross sections from the reaction cross sectionsmore » obtained from the OM fits to the elastic-scattering data, and these fusion data were found to be consistent. The CCDEF calculations describe these data quite well. A comparison of the fusion data for the {sup 7}Be+{sup 27}Al and {sup 7}Li+{sup 27}Al systems shows a similar and consistent behavior.« less
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