Molecular superfluidity studied in helium as a function of the thermodynamic state using a corona discharge

Superfluidity is a many-body quantum effect observed in liquid helium. Macroscopic superfluidity can be probed by means of a torsional pendulum immersed in liquid helium; changes in the temperature of the system from the lambda point of helium (2.17K) down to 1K lead to an increase in the moment of inertia of the pendulum [1]. Its microscopic analogue would be obtained by replacing the torsional pendulum with a rotating molecule; however, the realization of a bulk experiment is very difficult since at the low temperatures of liquid helium all foreign molecules would freeze at the container walls.

In order to overcome this difficulty we use a corona discharge to excite short lived helium excimers in Rydberg states. Such excimers emit fluorescence and we were able to resolve rotational lines in its spectrum, thereby sensitively probing the environment. Rotational resolution has been obtained in molecule-doped helium droplets before, but here we are able to measure temperature and pressure dependence for the first time.

Preliminary results show the rotationally resolved excimer fluorescence can be observed in helium at 1 bar and at 300K, 77K and 4K. These preliminary measurements also show that the effective moment of inertia of the excimers change depending on the temperature. In order to investigate if the density effect can be observed at room temperature we observed rotationally resolved lines from 1 bar until 25 bar. We did not observe a changing moment of inertia in this range at 300K.

[1] Andronikashvili, E.: 1971, `A direct observation of two kinds of motion in liquid helium II’. In: translated by Z.M. Galasiewicz (ed.): Helium 4. Oxford: Pergamon, pp. 154-165.

[2] J. P. Toennies and A. F. Vilesov, Angew. Chemie Int. Ed. 43, 2622 (2004).

Lifshitz-like solutions with hyperscaling violation in ungauged supergravity

We present a formalism that allows to construct, for each static and spherically symmetric black hole solution of ungauged supergravity, a non-trivial gravitational solution whose asymptotics exhibit both a dynamical critical exponent z and a hyperscaling violation exponent θ, without the need of solving any equation of motion. Therefore, we establish, in the context of four dimensional ungauged supergravity, a new correspondence between both kinds of solutions, which allows to write the radius of the Lifshitz-like metric in terms of the physical parameters of the dual asymptotically flat, static black hole via a universal relation. The new Lifshitz-like solutions, being solutions of ungauged supergravity, can be easily embedded in String Theory.

Importance of Higher Twist Effects in Diffractive Deep Inelastic Scattering

We present our QCD analysis of the diffractive pomeron structure function. We consider Pomeron as an object with parton distribution function, evolving according to the NLO DGLAP equations within the framework of the ‘Fixed Flavour Number Scheme’. A remarkable feature of DDIS is the dominance of the twist-4 contribution for small diffractive masses. We quantify this effect and find a reasonable good agreement between the predictions and the data. We predict longitudinal and charm proton diffractive structure function as well. Our results are compared with other analysis from the literature.

Gravitational-thermodynamic instabilities in dS and AdS

We investigate the effect of a cosmological constant on the gravito-thermal instability. A spherically symmetric self-gravitating gas is studied as a thermodynamic system with long range interactions in the micro-canonical ensemble. The onset of the instability is calculated by the second order variation of the entropy and Poincare’s theory of series of equilibria. In the Newtonian limit of dS, the system presents a novel `reentrant behaviour’; in addition to the Antonov radius we find a second critical radius, where a series of local entropy maxima is restored. The relationship with Schwarzschild-dS system is investigated. The Tolman-Oppenheimer-Volkov equation with a cosmological constant is derived as a thermodynamic equilibrium equation by maximization of the entropy. For several equations of state the full general relativistic system is studied in the thermodynamic framework and the onset of instability is calculated.

Can effects of Quantum Gravity be observed in the Cosmic Microwave Background?

We investigate the question whether small quantum-gravitational effects can be observed in the anisotropy spectrum of the cosmic microwave background radiation. An observation of such an effect is needed in order to discriminate between different approaches to quantum gravity. Using canonical quantum gravity with the Wheeler-DeWitt equation, we find a suppression of power at large scales. Current observations only lead to an upper bound on the energy scale of inflation, but the framework is general enough to study other situations in which such effects might indeed be seen.

Geometry of almost-product (pseudo-)Riemannian manifolds and the dynamics of the observer

In an original formulation of Einstein’s general relativity a gravitation field is represented by a metric on (curved) space-time which satisfies Einstein’s equations. An observer was automatically determined by a choice of a coordinate system. A notion of the observer has evolved since then; nowadays there are a few optional ways of looking at that problem: word-line of a point particle (V. Bolos), congruence of such lines, i.e. field of instantaneous observers represented by a unit vector field – an arrow of time (J. Ehlers), tetrad field i.e. an orthonormal frame of vector fields, etc. In the presented work we were dealing with the notion of the observer as an one-dimensional time-like distribution on space-time represented by the normalized vector field (arrow of time). Therefore, our observer is independent of the gravitational field and can be defined independently of the coordinate system. It turns out that a pair: the metric and the vector field determines a geometrical object on a space-time manifold which is called almost-product (Lorentzian) structure. Its properties allow to categorize pseudo-Riemannian manifolds with such structures. It turn out that we have two main classes of the observers: inertial (geodesic) and accelerated ones. Further calculations showed that there are 8 subclasses for each of them which are related to the geometry of the corresponding three-dimensional orthogonal distributions; e.g. integrable (foliation), umbilical, minimal. We have associated above mentioned geometric characteristics with the ones introduced by J. Ehlers (acceleration, rotation, shear, expansion) which describe the dynamics of the observer.

The concept of excess-heat in non-equilibrium statistical mechanics

I will discuss equilibrium states and the Clausius relation. Consider a system between 2 heat baths with the same inverse temperature. When the temperature is changed, the system will relax to a new equilibrium. The total heat exchanged is finite. When dealing with non-equilibrium stationary states, a constant heat flux is present, and when temperatures are changed, the exchanged heat is proportional with time. However, one is interested in the netto change of heat, which is not proportional with time. It seems that the concept of excess heat captures the netto heat transfer here.

Design of a very thin Internal target for the anti-proton ring at FAIR

The future facility FAIR (Facility for Antiproton and Ion Research) with its intense beams will include the HESR ring (High Energy Storage Ring), where the PANDA experiment will be located. High energy community tries to investigate very rare reactions (production of strange baryons, formation of heavy quark systems) using quite rare projectiles like antiprotons or kaons (1,2). The beams are difficult to be produced in large amount, it becomes mandatory to avoid as much as possible to waste them. A way to recover the transmitted particles is to insert the target inside the beam pipe of a storage ring. This is the case of the experiment PANDA at FAIR, which will reach high luminosity using antiprotons, accumulated in HESR (High Energy Storage Ring), against internal targets of ( 12C) for the hypernuclear physics and of LH2 for the meson spectroscopy.

The material of the target is determined by the optimization of the hyperon production: therefore, shape and sizes plays a crucial role in minimizing the above mentioned effects. A prototype of a very thin, wire shaped target has been already designed and realized. The technique used to shape the material (12C) into a wire 3 μm thick and 10 μm wide will be described and the results of the applied tests will be reported. The calculations of the most suitable beam time structure for optimizing the hyperon production will be also presented.

(1) K.Szymanska et al., Acta Phys. Pol. B 41, 285 (2010)

(2) K. Tanida et al. Hyperfine Interact. 193, 81 (2009)

(3) F. Iazzi, Few-Body Systems, vol. 43, no.1, pp. 97 (2008)

Holographic Thermalization

In this talk I will try to highlight how the gauge/gravity duality can be used to study the thermalization of strongly coupled gauge theories, and I will also mention some of its problems. Thereafter I will illustrate this with some of my own calculations, which involves numerically evolving Einstein’s equations and hence studying thermalization in the dual field theory.

The observable-state model for quantum field theory

The purpose of the talk is to introduce a new development of the quantum field theory that we have called “The observable-state model” [1,2], which consists in the description of the perturbation expansion of the correlation functions in terms of mean values of observables on particular quantum states. The main advantage of this development is the renormalization procedure, that can be described as a projection operation which removes the short-distance singularities of the quantum states, leaving any correlation function finite even if the interacting Lagrangian is not renormalizable.

[1] J. S. Ardenghi, M. Castagnino, Phys, Rev. D. 85, 12, 025002, 2012

[2] J. S. Ardenghi, M. Castagnino, Phys, Rev. D, 85, 15, 125008, 2012.