Frankfurt Institute for Advanced Studies

About: Frankfurt Institute for Advanced Studies is a facility organization based out in Frankfurt am Main, Germany. It is known for research contribution in the topics: Baryon & Quark–gluon plasma. The organization has 798 authors who have published 2733 publications receiving 82799 citations. The organization is also known as: FIAS.

Particle number fluctuations for the van der Waals equation of state

Abstract: The van der Waals (VDW) equation of state describes a thermal equilibrium in system of particles, where both repulsive and attractive interactions between them are included. This equation predicts the existence of the first order liquid–gas phase transition and the critical point. The standard form of the VDW equation is given by the pressure function in a canonical ensemble (CE) with a fixed number of particles. In this paper the VDW equation is derived within the grand canonical ensemble (GCE) formulation. We argue that this procedure can be useful for new physical applications, in particular, the fluctuations of the number of particles, which are absent in the CE, can be studied in the GCE. For the VDW equation of state in the GCE the particle number fluctuations are calculated for the whole phase diagram, both outside and inside the liquid–gas mixed phase region. It is shown that the scaled variance of these fluctuations remains finite within the mixed phase and goes to infinity at the critical point. The GCE formulation of the VDW equation of state can also be an important step for its application in the statistical description of hadronic systems, where numbers of different particle species are usually not conserved.

Test-particle dynamics in general spherically symmetric black hole spacetimes

Abstract: To date, the most precise tests of general relativity have been achieved through pulsar timing, albeit in the weak-field regime. Since pulsars are some of the most precise and stable ``clocks'' in the Universe, present observational efforts are focused on detecting pulsars in the vicinity of supermassive black holes (most notably in the Galactic Centre), enabling pulsar timing to be used as an extremely precise probe of strong-field gravity. In this paper, a mathematical framework to describe test-particle dynamics in general black-hole spacetimes is presented and subsequently used to study a binary system comprising a pulsar orbiting a black hole. In particular, taking into account the parameterization of a general spherically symmetric black-hole metric, general analytic expressions for both the advance of the periastron and for the orbital period of a massive test particle are derived. Furthermore, these expressions are applied to four representative cases of solutions arising in both general relativity and in alternative theories of gravity. Finally, this framework is applied to the Galactic center $S$-stars and four distinct pulsar toy models. It is shown that by adopting a fully general-relativistic description of test-particle motion which is independent of any particular theory of gravity, observations of pulsars can help impose better constraints on alternative theories of gravity than is presently possible.

Nuclear fragmentation reactions in extended media studied with Geant4 toolkit

Abstract: It is well-known from numerous experiments that nuclear multifragmentation is a dominating mechanism for production of intermediate mass fragments in nucleus–nucleus collisions at energies above 100 A MeV . In this paper we investigate the validity and performance of the Fermi break-up model and the statistical multifragmentation model implemented as parts of the Geant4 toolkit. We study the impact of violent nuclear disintegration reactions on the depth-dose profiles and yields of secondary fragments for beams of light and medium-weight nuclei propagating in extended media. Implications for ion-beam cancer therapy and shielding from cosmic radiation are discussed.

Third harmonic flow of charged particles in Au plus Au collisions at root s(NN)=200 GeV

Abstract: We report measurements of the third harmonic coefficient of the azimuthal anisotropy, upsilon(3), known as triangular flow. The analysis is for charged particles in Au + Au collisions at root s(NN) = 200 GeV, based on data from the STAR experiment at the BNL Relativistic Heavy Ion Collider. Two-particle correlations as a function of their pseudorapidity separation are fit with narrow and wide Gaussians. Measurements of triangular flow are extracted from the wide Gaussian, from two-particle cumulants with a pseudorapidity gap, and also from event plane analysis methods with a large pseudorapidity gap between the particles and the event plane. These results are reported as a function of transverse momentum and centrality. A large dependence on the pseudorapidity gap is found. Results are compared with other experiments and model calculations.

Spectra of secondary electrons generated in water by energetic ions.

Abstract: The energy distributions of secondary electrons produced by energetic carbon ions (in the energy range used, e.g., in hadron therapy), incident on liquid water, are discussed. For low-energy ions, a parametrization of the singly differential ionization cross sections is introduced, based on tuning the position of the Bragg peak. The resulting parametrization allows a fast calculation of the energy spectra of secondary electrons at different depths along the ion's trajectory, especially near the Bragg peak. At the same time, this parametrization provides penetration depths for a broad range of initial-ion energies within the therapeutically accepted error. For high-energy ions, the energy distribution is obtained with a use of the dielectric-response function approach. Different models are compared and discussed.