Narrow Results

For any local, translation-covariant quantum field theory on Minkowski spacetime, we prove that two distinct states that are invariant under the inertial time evolutions in different inertial reference frames are disjoint, i.e. neither state is a perturbation of the other, if the states are primary, have separating Gelfand–Naimark–Segal (GNS) vectors, and satisfy a timelike cluster property called the mixing property. These conditions are fulfilled by the inertial Kubo–Martin–Schwinger (KMS) states of the free scalar field, thus showing that a state satisfying the KMS condition relative to one inertial frame is far from thermal equilibrium relative to other inertial frames. We review the property of return to equilibrium (RTE) in open quantum systems theory and discuss the implications of disjointness on the asymptotic behavior of detector systems coupled to states of a free massless scalar field. We argue that the coupled system of an Unruh–DeWitt detector moving with constant velocity relative to the field in a KMS state, or an excitation thereof, cannot thermalize under generic conditions. This leads to an illustration of the physical differences between heat baths in inertial systems and the alleged “heat bath” of the Unruh effect. This paper also sketches the construction and RTE property of the quantum dynamical system of an Unruh–DeWitt detector coupled to a massless scalar field in a KMS state relative to the inertial rest frame of the detector.

In this paper, within the framework of open-system dynamics, we investigate the thermalization phenomena of Unruh effect and de Sitter spacetime. It is shown that the Unruh effect, thermal effect of de Sitter spacetime and Hawking effect are similar in nature.

We consider a possible mechanism of thermalization of nucleons in relativistic heavy-ion collisions. Our model belongs, to a certain degree, to the transport ones; we investigate the evolution of the system created in nucleus–nucleus collision, but we parametrize this development by the number of collisions of every particle during evolution rather than by the time variable. We based on the assumption that the nucleon momentum transfer after several nucleon–nucleon (–hadron) elastic and inelastic collisions becomes a random quantity driven by a proper distribution. This randomization results in a smearing of the nucleon momenta about their initial values and, as a consequence, in their partial isotropization and thermalization. The trial evaluation is made in the framework of a toy model. We show that the proposed scheme can be used for extraction of the physical information from experimental data on nucleon rapidity distribution.

We review the color glass condensate effective theory, that describes the gluon content of a high energy hadron or nucleus, in the saturation regime. The emphasis is put on applications to high energy heavy ion collisions. After describing initial state factorization, we discuss the glasma phase, that precedes the formation of an equilibrated quark–gluon plasma. We end this review with a presentation of recent developments in the study of the isotropization and thermalization of the quark–gluon plasma.

Our understanding of the state of the universe between the end of inflation and big bang nucleosynthesis (BBN) is incomplete. The dynamics at the end of inflation are rich and a potential source of observational signatures. Reheating, the energy transfer between the inflaton and Standard Model fields (possibly through intermediaries) and their subsequent thermalization, can provide clues to how inflation fits in with known high-energy physics. We provide an overview of our current understanding of the nonperturbative, nonlinear dynamics at the end of inflation, some salient features of realistic particle physics models of reheating, and how the universe reaches a thermal state before BBN. In addition, we review the analytical and numerical tools available in the literature to study preheating and reheating and discuss potential observational signatures from this fascinating era.

We investigate the conditions under which particle multiplicities in high energy collisions are Boltzmann distributed, as is the case for hadron production in e⁺e^-, pp, and heavy ion collisions. We show that the apparent temperature governing this distribution does not necessarily imply equilibrium (thermal or chemical) in the usual sense. We discuss an explicit example using tree level amplitudes for N photon production in which a Boltzmann-like distribution is obtained without any equilibration. We argue that the failure of statistical techniques based on free particle ensembles may provide a signal for collective phenomena (such as large shifts in masses and widths of resonances) related to the QCD phase transition.

The recent discussion about experimental evidence for pentaquark states has revitalized the interest in exotic hadrons. If such states really exist, it is natural to assume that they will be formed at the late hadronization stage of ultra-relativistic heavy ion collisions, given the success of quark recombination models in the description of hadronization. Here, we apply the qMD model to study the formation of color neutral exotic multi-quark clusters at hadronization. We search for color neutral clusters made up of up to six color charges, respectively. We thus obtain estimates for the numbers and phase space distributions of exotic hadronic states produced by clustering in heavy ion collisions, including the members of the pentaquark multiplets. We obtain particle abundances that are smaller than thermal model predictions. Moreover, the results obtained in recombination from ultra-relativistic heavy ion collisions can be compared to the estimates based on equal population of the corresponding multiplets, and to results from fully thermalized systems. We find that the distribution of exotic hadrons from recombination over large multiplets provides a sensitive signal for thermalization and decorrelation of the initial, non-equilibrium state of the collision.

We review current ideas on entropy production during the different stages of a relativistic nuclear collision. This includes recent results on decoherence entropy and the entropy produced during the hydrodynamic phase by viscous effects. We start by a discussion of decoherence caused by gluon bremsstrahlung in the very first interactions of gluons from the colliding nuclei. We then present a general framework, based on the Husimi distribution function, for the calculation of entropy growth in quantum field theories, which is applicable to the early ("glasma") phase of the collision during which most of the entropy is generated. The entropy calculated from the Husimi distribution exhibits linear growth when the quantum field contains unstable modes and the growth rate is asymptotically equal to the Kolmogorov–Sinaï entropy. We outline how the approach can be used to investigate the problem of entropy production in a relativistic heavy ion reaction from first principles. We show that the same result can be obtained in the framework of a completely different approach called eigenstate thermalization hypothesis. Finally we discuss some recent results on entropy production in the strong coupling limit, as obtained from AdS/CFT duality.

In relativistic heavy-ion collisions, a highly occupied gluonic matter is created shortly after initial impact, which is in a nonthermal state and often referred to as the Glasma. Successful phenomenology suggests that the glasma evolves rather quickly toward the thermal quark–gluon plasma (QGP) and a hydrodynamic behavior emerges at a very early time ~ô(1) fm/c. Exactly how such "apparent thermalization" occurs and connects the initial conditions to the hydrodynamic onset, remains a significant challenge for theory as well as phenomenology. We briefly review various ideas and recent progress in understanding the approach of the glasma to the thermalized QGP, with an emphasis on the kinetic theory description for the evolution of such far-from-equilibrium and highly overpopulated, thus weakly-coupled yet strongly interacting glasma.

In this review, I present the description of the early stages of heavy ion collisions at high energy in the Color Glass Condensate framework, from the pre-collision high energy nuclear wave function to the point where hydrodynamics may start becoming applicable.

Gauge/gravity duality has provided unprecedented opportunities to study dynamics in certain strongly coupled gauge theories. This review aims to highlight several applications to heavy ion collisions including far-from-equilibrium dynamics, hydrodynamics and jet energy loss at strong coupling.

Embedded random matrix ensembles generated by random interactions (of low body rank and usually two-body) in the presence of a one-body mean field, introduced in nuclear structure physics, are now established to be indispensable in describing statistical properties of a large number of isolated finite quantum many-particle systems. Lie algebra symmetries of the interactions, as identified from nuclear shell model and the interacting boson model, led to the introduction of a variety of embedded ensembles (EEs). These ensembles with a mean field and chaos generating two-body interaction generate in three different stages, delocalization of wave functions in the Fock space of the mean-field basis states. The last stage corresponds to what one may call thermalization and complex nuclei, as seen from many shell model calculations, lie in this region. Besides briefly describing them, their recent applications to nuclear structure are presented and they are (i) nuclear level densities with interactions; (ii) orbit occupancies; (iii) neutrinoless double beta decay nuclear transition matrix elements as transition strengths. In addition, their applications are also presented briefly that go beyond nuclear structure and they are (i) fidelity, decoherence, entanglement and thermalization in isolated finite quantum systems with interactions; (ii) quantum transport in disordered networks connected by many-body interactions with centrosymmetry; (iii) semicircle to Gaussian transition in eigenvalue densities with $k$-body random interactions and its relation to the Sachdev–Ye–Kitaev (SYK) model for majorana fermions.

Boson intensity correlations were examined to explore the fluid characterization produced in the collisions at the largest colliders and were perceived to have an astonishing curtailment during the computation of three-pion quantum interferences. Such analogous suppression can be probed to investigate the characteristics of particle production sources created during the collisions of heavy nuclei at unprecedented energies. We have demonstrated and analyzed the particle emissions from radiated sources with Bose–Einstein coherence that induces three-particle interferences to investigate the peculiarity of the particle emitted fluids. We are perspicacious that the bosons resemble the pertinent aspirant of coherence, and the normalized three-particle correlations evaluate the occurrence of such conglomerate fluid phases of chaotic and coherence significantly. Moreover, we also explored and analyzed the cumulant and the normalized correlations to examine the specific features of particle emission sources during the smashing of heavy nuclei. With such particular and pioneering approach, we have observed a consequential difference in the three-particle correlations and the normalized correlator at small temperature regimes.

In this paper, we investigated the influence of temperature and momentum-dependent coherence-chaos radiations on particle excretion from a fluid with quantum supremacy. The dynamics interpretation of a system can become exceedingly complex and femtoscopy is an efficient quantum tool that captures and explores the complicated dynamical properties. This research presents a comprehensive and brief analysis of fluid in the context of quantum interference for partially chaotic systems, as well as novel findings for chaos synchronization of identical bosons in the extending source are evaluated. The eminence of coherence on chaotic production has been demonstrated using correlation plots in the existence of the quantum influence. The temperature profile is described with the mitigation of graphs created for various flow peculiarities, and the density equations are derived through feasible interferences transformation approaches. Results exhibit the quantitative data of chaotic and droplets exhibiting coherence features and illustrate a premise that depicts motivated conversions between cold and hot bosonic particles crossover during the expanding of emitted sources. The emergent phase can contain a partially thermalized distribution of particles which is elucidated by the swiftness of the hadronic transition and this phase reveals marvelous entirely quantum correlations according to our findings. In particular, we formulate the normalized interception for the hybrid system using particular methods to probe the source configurations.

The quest for a microscopic foundation of thermodynamics is addressed within the Nonunitary Newtonian Gravity (NNG) model through the study of a specific closed system, namely, a three-dimensional harmonic nanocrystal. A numerical calculation of the nanocrystal von Neumann entropy as a function of time is performed, showing a sharp monotonic increase, followed by a stabilization at late times. This behavior is consistent with the emergence of a microcanonical ensemble within the initial energy levels, signaling, in this way, the establishment of a nonunitary gravity-induced thermal equilibrium.

Many-particle quantum walks of particles obeying Bose statistics, moving on graphs of various topologies are introduced. A single coin tossing commands the conditional shift operation over the whole graph. Vertex particle densities, mean values of phase space variables, second order spatial correlations and counting statistics are evaluated and simulated. The evidence of universal dynamics is presented.

We examine the dynamics of entanglement entropy of all parts in an open system consisting of a two-level dimer interacting with an environment of oscillators. The dimer-environment interaction is almost energy conserving. We find the precise link between decoherence and production of entanglement entropy. We show that not all environment oscillators carry significant entanglement entropy and we identify the oscillator frequency regions which contribute to the production of entanglement entropy. For energy conserving dimer-environment interactions the models are explicitly solvable and our results hold for all dimer-environment coupling strengths. We carry out a mathematically rigorous perturbation theory around the energy conserving situation in the presence of small non-energy conserving interactions.

We studied the evolution of Wightman correlator in a thermalizing state using holography. We gave a prescription for calculating the correlator in coordinate space. For equal-time correlator 〈O(v, x)O(v, 0)〉, we obtained an enhancement factor v² due to long range correlation present in the initial state. This was missed by previous studies based on geodesic approximation. We also studied spatially integrated correlator and presented evidence indicating that our intuition from equilibrium physics is not necessarily true for a far-from-equilibrium state. We also calculated radiation spectrum of particle weakly coupled to O and found low frequency mode thermalizes faster than high frequency mode.

The following sections are included:

• Ultrafast Processes in Semiconductors
• Ultrafast Processes in Metal Nanoparticles
• Ultrafast Processes in Quantum Dots
• References

We analyze, in the framework of open quantum systems, the reduced dynamics of a static detector (a two-level atom) outside a two-dimensional black hole in weak interaction with a bath of massless quantum scalar fields in the Hartle-Hawking vacuum. We find that the detector outside the black hole is asymptotically driven to a thermal state at the temperature T, which reduces to the Hawking temperature in the spatial asymptotic region, regardless of its initial state. Our discussion therefore shows that the Hawking effect can be understood as a manifestation of thermalization phenomena in the framework of open quantum systems.