The quark gluon plasma: Lattice computations put to experimental test

I describe how lattice computations are being used to extract experimentally relevant features of the quark gluon plasma. I deal specifically with relaxation times, photon emissivity, strangeness yields, event-by-event fluctuations of conserved quantities and hydrodynamic flow. Finally I give evidence that the plasma is rather liquid-like in some ways.     

Shape space methods for quantum cosmological triangleland

With toy modelling of conceptual aspects of quantum cosmology and the problem of time in quantum gravity in mind, I study the classical and quantum dynamics of the pure-shape (i.e. scale-free) triangle formed by 3 particles in 2-d. I do so by importing techniques to the triangle model from the corresponding 4 particles in 1-d model, using the fact that both have 2-spheres for shape spaces, though the latter has a trivial realization whilst the former has a more involved Hopf (or Dragt) type realization. I furthermore interpret the ensuing Dragt-type coordinates as shape quantities: a measure of anisoscelesness, the ellipticity of the base and apex’s moments of inertia, and a quantity proportional to the area of the triangle. I promote these quantities at the quantum level to operators whose expectation and spread are then useful in understanding the quantum states of the system. Additionally, I tessellate the 2-sphere by its physical interpretation as the shape space of triangles, and then use this as a back-cloth from which to read off the interpretation of dynamical trajectories, potentials and wavefunctions. I include applications to timeless approaches to the problem of time and to the role of uniform states in quantum cosmological modelling.     

Why Gauge?

The world appears to be well described by gauge theories; why? I suggest that gauge is more than mathematical redundancy. Gauge-dependent quantities can not be predicted, but there is a sense in which they can be measured. They describe “handles” though which systems couple: they represent real relational structures to which the experimentalist has access in measurement by supplying one of the relata in the measurement procedure itself. This observation leads to a physical interpretation for the ubiquity of gauge: it is a consequence of a relational structure of physical quantities.     

Quantifying the Autonomy of Structurally Diverse Automata: A Comparison of Candidate Measures

Should the internal structure of a system matter when it comes to autonomy? While there is still no consensus on a rigorous, quantifiable definition of autonomy, multiple candidate measures and related quantities have been proposed across various disciplines, including graph-theory, information-theory, and complex system science. Here, I review and compare a range of measures related to autonomy and intelligent behavior. To that end, I analyzed the structural, information-theoretical, causal, and dynamical properties of simple artificial agents evolved to solve a spatial navigation task, with or without a need for associative memory. By contrast to standard artificial neural networks with fixed architectures and node functions, here, independent evolution simulations produced successful agents with diverse neural architectures and functions. This makes it possible to distinguish quantities that characterize task demands and input-output behavior, from those that capture intrinsic differences between substrates, which may help to determine more stringent requisites for autonomous behavior and the means to measure it.     

Dynamics of test black holes

The concept of a test object is introduced. The definition includes mini black holes. This test-particle concept makes it possible to introduce unambiguously the concept of a background space-time. Noether's theorem is then used to introduce dynamical quantities for test objects, and this has made it possible to generalize covariantly Papapetrou's energy-momentum pseudotensor for the case of a curved background space-time. The additional use of the nonradiative approximation and allowance for the zeroth and first moments of the dynamical quantities leads to the conclusion that the motion of a test object (including mini black holes) satisfies the Mathisson-Papapetrou equations. This result is achieved by taking into account the gravitational field of the test object itself in the integral dynamical quantities.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 57–61, February, 1981.I am sincerely grateful to N. V. Mitskevich for a helpful discussion of the subject and support during the work.     

Determination of absolute atomic transition probabilities using time resolved optical pumping

We describe a method of determining atomic transition probabilities by independently measuring branching ratios and radiative lifetimes. These quantities are directly determined by time resolved optical pumping. The technique has been applied to the measurement of gA values for particular transitions in ²³⁸U I.     

Perturbed Arcs in Turbulent Axial Gas Flow II. Fluctuating Local Properties

As a continuation of the research described in Pt. I, local quantities are studied experimentally by electrostatic wall probing, time resolving shadowgraphy and radial luminosity profile scanning of arcs in turbulent axial gas flow. Turbulency of the gas coolant and thermal sheath properties are discussed as well as the consequencies of the gathered knowledge to theoretical modelling.     

Dynamical measures of density in exotic cosmologies

I examine the evolution of density fluctuations and compute the global density inferred by standard dynamical methods in various exotic cosmological models, where a significant portion of the present mass density is not fairly sampled by galaxies. In such models, these standard measures give incorrect results. The naive expectation, that the apparent fraction of critical density Ω is equal to the fraction of mass in galaxies, $\text{Ω = α}$, is a slightly modified in the full calculation. The presence of an exotic component relieves some cosmological problems and aggravates others, and can be detected observationally by comparing quantities dependent on expansion rate with quantities dependent on curvature.     

A self-consistent approach to the localization-delocalization problem of the quantum Hall effect

I present a semi-phenomenological framework for the calculation of the Kubo conductivities in 2d systems subject to a magnetic field based on the memory function formalism. The notion of a memory oscillation time is introduced and its peculiar role related to the orientation dependent quantities in magnetic fields is discussed. Self-consistency equations are formulated which allow to approach the localization-delocalization transition. I study the Hall conductivity and the longitudinal conductivity in the low temperature limit and find that they are related by a universal relation refered to as stable trajectories in renormalization group approaches on the QHE.     

Observables in a schwarzchild field

An analysis is given of the problem of defining observables, i.e., quantities which can be measured by actual observers. The notion of fundamental observables is introduced; these are obtained by the projection of tensors into the reference system of observers falling freely in a gravitational field. The significance of these concepts is illustrated by means of an example, wherein the gravitational field of a static spherically symmetric source is analyzed.In conclusion, I am deeply grateful to V. I. Rodichev and G. I. Zadonskii for very interesting conversations on the subject discussed here.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 16, No. 9, pp. 103–107, September, 1973.     

Discontinuities in the solutions of Einstein's equations

The quantities that determine the jump conditions for discontinuities in the second derivatives of the components of the metric tensor are obtained.Translated from Izvestiya Vysshykh Uchebnykh Zavedenii, Fizika, No. 10, pp. 40–43, October,1981.I take this opportunity to express my deep gratitude to L. R. Volevich for his constant attention to my work.     

The single photon superradiance from the eigenmode analysis

Using the eigenmode analysis of the scalar photon theory, I compute the probability of the atoms remaining excited and the probability for the atoms remaining in the initial quantum state of a system of two-level atoms cloud in a sphere initially prepared to radiate in the forward direction, i.e., the single photon superradiance problem. The convergence in the results obtained for increasingly larger radii for the sphere suggests that the asymptotic limits for these quantities are obtained for a sphere with a radius equal to six times the resonant wavelength. I predict the maximal value of the probability of secondary excited states from large spheres at 17.1%.     

Stoßbestimmte Relaxation des Elektronenensembles im Plasma bei zusätzlicher Aufheizung durch ein elektrisches Feld I. Die charakteristischen Zeiten für den Übergang in stationäre Zustände

Collision Dominated Relaxation of the Electron Ensemble in a Plasma with Additional Heating by an Electric Field. I. Characteristic Times for the Transition to Stationary States Starting from time dependent Boltzmann equation for electrons the time development of the isotropic part of the distribution function and of macroscopic quantities as mean energy, mobility, excitation frequency and energy transfer quotients during transition between two stationary states are determined. The computation is referred to weak ionized neon plasmas which are typical for low pressure and for medium pressure discharges. As a result of this investigations we get informations about the characteristic relaxation times which are different in order of magnitude, and about their dependence of the processes of energy transfer. The energy transfer quotients which determine the energy loss by different collision processes in consideration are found to be suitable quantities to characterize the relaxation times.     

Evaluations of Low-Energy Physical Quantities in QCD with IR Freezing of the Coupling

The \({{\overline{\rm MS}}}\) -like schemes in QCD have in general the running coupling which contains Landau singularities, i.e., singularities outside the timelike semi-axis, at low squared momenta. As a consequence, evaluation of the spacelike quantities, such as current correlators, in terms of (powers of) such a coupling then results in quantities which contradict the basic principles of quantum field theories. On the other hand, in those QCD frameworks where the running coupling remains finite at low squared momenta (IR freezing), the coupling usually does not have Landau singularities in the complex plane of the squared momenta. I argue that in such QCD frameworks the spacelike quantities should not be evaluated as a power series, but rather as a series in derivatives of the coupling with respect to the logarithm of the squared momenta. Such series show considerably better convergence properties. Moreover, Padé-related resummations of such logarithmic derivative series give convergent series, thus eliminating the practical problem of series divergence due to renormalons.     

Nonlinear relaxation of thermodynamic quantities

Under the assumption of local equilibrium, a relaxation equation is obtained for macroscopic quantities, this generalizing the linear relations of nonequilibrium thermodynamics to the nonequilibrium case.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 65–68, April, 1980.I thank G. F. Efremov, V. B. Tsaregradskii, and G. N. Bochkov for discussing the results.     

Expanding the Area of Gravitational Entropy

I describe how gravitational entropy is intimately connected with the concept of gravitational heat, expressed as the difference between the total and free energies of a given gravitational system. From this perspective one can compute these thermodyanmic quantities in settings that go considerably beyond Bekenstein's original insight that the area of a black hole event horizon can be identified with thermodynamic entropy. The settings include the outsides of cosmological horizons and spacetimes with NUT charge. However the interpretation of gravitational entropy in these broader contexts remains to be understood.     

Alien calculus and non perturbative effects in Quantum Field Theory

In many domains of physics, methods for dealing with non-perturbative aspects are required. Here, I want to argue that a good approach for this is to work on the Borel transforms of the quantities of interest, the singularities of which give non-perturbative contributions. These singularities in many cases can be largely determined by using the alien calculus developed by Jean Écalle. My main example will be the two point function of a massless theory given as a solution of a renormalization group equation.     

Solution of the master equation for quantum systems weakly coupled to reservoirs and far from thermal equilibrium

The Liouville operator of the master equation is decomposed into a part describing the proper system and another operator describing the interaction of the proper system with a set of reservoirs. If the motion of the proper system is described by a Hamiltonian, the corresponding solutions of the density matrix equation are spanned by all conserved quantities and are thus highly degenerate. We demonstrate how this degeneracy may be lifted by applying some sort of perturbation theory for degenerate systems. If there is only one relevant conserved quantity and if the heatbaths connect the quantum numbers of this conserved quantity by nearest-neighbour steps, the solution of the problem can be found explicitly. Otherwise the solution of the original master equation is reduced to a much simpler master equation of orderN, whereN is the number of conserved quantities. An application to a new type of parametric processes in nonlinear optics is given.