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The de-Sitter spacetime is a maximally symmetric Lorentzian manifold with constant positive scalar curvature that plays a fundamental role in modern cosmology. Here, we investigate bulk-viscosity-assisted quasi de-Sitter inflation, that is the period of accelerated expansion in the early universe during which −𝐻˙≪𝐻2 , with 𝐻(𝑡) being the Hubble expansion rate. We do so in the framework of a causal theory of relativistic hydrodynamics, which takes into account non-equilibrium effects associated with bulk viscosity, which may have been present as the early universe underwent an accelerated expansion. In this framework, the existence of a quasi de-Sitter universe emerges as a natural consequence of the presence of bulk viscosity, without requiring introducing additional scalar fields. As a result, the equation of state, determined by numerically solving the generalized momentum-conservation equation involving bulk viscosity pressure turns out to be time dependent. The transition timescale characterising its departure from an exact de-Sitter phase is intricately related to the magnitude of the bulk viscosity. We examine the properties of the new equation of state, as well as the transition timescale in the presence of bulk viscosity pressure. In addition, we construct a fluid description of inflation and demonstrate that, in the context of the causal formalism, it is equivalent to the scalar field theory of inflation. Our analysis also shows that the slow-roll conditions are realised in the bulk-viscosity-supported model of inflation. Finally, we examine the viability of our model by computing the inflationary observables, namely the spectral index and the tensor-to-scalar ratio of the curvature perturbations, and compare them with a number of different observations, finding good agreement in most cases.
We here investigate bulk-viscosity driven quasi de-Sitter inflation, that is, the period of accelerated expansion in the early universe during which −H˙≪H2, with H(t) being the Hubble expansion rate. We do so in the framework of a causal theory of relativistic hydrodynamics that takes into account non-equilibrium effects associated to bulk viscosity that may be present as the early universe undergoes an accelerated expansion. In this framework, the existence of a quasi de-Sitter universe emerges as a natural consequence of the presence of bulk viscosity, without requiring to introduce additional scalar fields. As a result, the equation of state, determined by numerically solving the generalized momentum-conservation equation involving bulk-viscosity pressure turns out to be time-dependent. The transition timescale characterising its departure from an exact de-Sitter phase is intricately related to the magnitude of the bulk viscosity. We examine the properties of the new equation of state, as well as the transition timescale in presence of bulk-viscosity pressure. In addition, we construct a fluid description of inflation and demonstrated that, in the context of the causal formalism, it is equivalent to the scalar field theory of inflation. Our analysis also shows that the slow-roll conditions are realised in the bulk-viscosity supported model of inflation. Finally, we examine the viability of our model by computing the inflationary observables, namely, the spectral index and the tensor-to-scalar ratio of the curvature perturbations, and compare them with a number of different observations finding good agreement in most cases.
We here investigate bulk-viscosity driven quasi de-Sitter inflation, that is, the period of accelerated expansion in the early universe during which −H˙≪H2, with H(t) being the Hubble expansion rate. We do so in the framework of a causal theory of relativistic hydrodynamics that takes into account non-equilibrium effects associated to bulk viscosity that may be present as the early universe undergoes an accelerated expansion. In this framework, the existence of a quasi de-Sitter universe emerges as a natural consequence of the presence of bulk viscosity, without requiring to introduce additional scalar fields. As a result, the equation of state, determined by numerically solving the generalized momentum-conservation equation involving bulk-viscosity pressure turns out to be time-dependent. The transition timescale characterising its departure from an exact de-Sitter phase is intricately related to the magnitude of the bulk viscosity. We examine the properties of the new equation of state, as well as the transition timescale in presence of bulk-viscosity pressure. In addition, we construct a fluid description of inflation and demonstrated that, in the context of the causal formalism, it is equivalent to the scalar field theory of inflation. Our analysis also shows that the slow-roll conditions are realised in the bulk-viscosity supported model of inflation. Finally, we examine the viability of our model by computing the inflationary observables, namely, the spectral index and the tensor-to-scalar ratio of the curvature perturbations, and compare them with a number of different observations finding good agreement in most cases.
Die zentralen Aussagen der Newtonschen Mechanik sind für Lernende erfahrungsgemäß nur schwierig zu erlernen. Hartnäckige, mit der physikalischen Theorie unvereinbare Schülervorstellungen erschweren Verbesserungen im Konzeptverständnis. Ein Grund dafür könnte der Fokus auf Idealsituationen im Unterricht sein. Lernende haben Schwierigkeiten, sich in diese Idealsituationen hineinzuversetzen und es besteht die Gefahr einer Kluft zwischen dem Unterricht und den real beobachtbaren Bewegungen im Alltag. Komplexe Alltagsbewegungen sind vor allem mathematisch kompliziert. Helfen kann hier Computereinsatz im Unterricht.
Die Studie im Prä-Post-Design mit N = 274 Schüler*innen der elften Jahrgangsstufe (nach G9) untersucht zwei unterschiedliche Arten, wie komplexe Bewegungen mit Reibung mithilfe des Computers (mathematische Modellbildung und Videoanalyse) diskutiert werden können. Dabei wird die Wirksamkeit eines Unterrichts mit Computereinsatz untersucht, mit dem die Newtonsche Dynamik nach dem schulischen Unterricht vertieft wird. Dazu wurden äquivalente Interventionen gestaltet, die sich zwischen den Gruppen nur in der Art des Computereinsatzes unterscheiden. In vier verschiedenen Aufgaben arbeiten die Schüler*innen nach einer Durchführung des jeweiligen Experiments in Zweiergruppen. Der eingesetzte Test basiert auf bekannten Tests und eigenen Items und wurde für diese Studie erstellt und pilotiert. Zudem wurden während einer Arbeitsphase von N = 45 Schüler*innen Bildschirmvideos mit Tonaufnahmen der Gespräche aufgenommen, um die Arbeitsweise analysieren zu können.
Im Konzeptverständnis der Dynamik zeigt sich ein signifikanter Unterschied zwischen Vor- und Nachtest mit großer Effektstärke in beiden Gruppen. Es gibt keinen Unterschied zwischen den beiden Varianten im gesamten Lernzuwachs. In Items zum ersten Newtonschen Gesetz mit Kräftekompensation verbessert sich die Gruppe der Modellbildung allerdings stärker. Dies könnte mit der stärkeren Reduktion der Schülervorstellung in der Gruppe der Modellbildung zusammenhängen, dass eine Kraft in Bewegungsrichtung wirken muss. Gleichzeitig zeigt sich in den angefertigten Aufnahmen der Schülergespräche, dass die Gruppe der Modellbildung diese Vorstellung in der Arbeitsphase häufiger aktiviert. Das Modellieren führt zu einem Explizieren der Schülervorstellung, welche dann durch den Vergleich von Modell und Messdaten durch die Software widerlegt wird. Dies reduziert die Schülervorstellung stärker. Die Gruppe der Modellbildung verbessert ihr Modellverständnis durch das Modellieren. Weitere Unterschiede (z. B. im Cognitive Load und affektiven Merkmalen) werden diskutiert.
Eine Mehrebenanalyse zeigt, dass der Vortest, das Interesse an theoretischen Zusammenhängen in der Physik, die kognitive Belastung und die Physiknote das Nachtestergebnis beeinflussen. Zudem zeigt ein Vergleich von erfolgreichen und weniger erfolgreichen Gruppen, dass die Phase der Ergebnissicherung und ein Zurückgreifen auf Modell bzw. Messdaten bei der Formulierung von Ergebnissen wichtig für den Lernerfolg sein könnten.
The Peking University Neutron Imaging Facility (PKUNIFTY) is being constructed, which is a compact acceleratordriven neutron source. The accelerator is a radio frequency quadrupole (RFQ) accelerator, which can deliver a 2 MeV deuteron beam. The neutrons are generated by deuterons bombarding beryllium target. The accelerator facility mainly consists of ECR (electron cyclotron resonance) ion source, LEBT (low energy beam transportation), RFQ cavity, HEBT (high energy beam transportation), RF transmitter and control system. This paper will introduce the requirements and design of that accelerator facility.
Working in a quenched setup with Wilson twisted mass valence fermions, we explore the possibility to compute non-perturbatively the step scaling function using the coordinate (X-space) renormalization scheme. This scheme has the advantage of being on-shell and gauge invariant. The step scaling method allows us to calculate the running of the renormalization constants of quark bilinear operators. We describe here the details of this calculation. The aim of this exploratory study is to identify the feasibility of the X-space scheme when used in small volume simulations required by the step scaling technique. Eventually, we translate our final results to the continuum MS scheme and compare against four-loop analytic formulae finding satisfactory agreement.
It has long been understood that the inclusion of temperature in the perturbative treatment of quantum field theories leads to complications that are not present at zero temperature. In these proceedings we report on the non-perturbative obstructions that arise, and how these lead to deviations in the predictions of lattice scalar correlation functions in massive e φ4 theory. Using the known non-perturbative spectral constraints satisfied by finite-temperature correlation functions we outline why the presence of distinct particle-like excitations could provide a resolution to these issues.
The properties of strongly-coupled lattice gauge theories at finite density as well as in real time have largely eluded first-principles studies on the lattice. This is due to the failure of importance sampling for systems with a complex action. An alternative to evade the sign problem is quantum simulation. Although still in its infancy, a lot of progress has been made in devising algorithms to address these problems. In particular, recent efforts have addressed the question of how to produce thermal Gibbs states on a quantum computer. In this study, we apply a variational quantum algorithm to a low-dimensional model which has a local abelian gauge symmetry. We demonstrate how this approach can be applied to obtain information regarding the phase diagram as well as unequal-time correlation functions at non-zero temperature.
The properties of strongly-coupled lattice gauge theories at finite density as well as in real time have largely eluded first-principles studies on the lattice. This is due to the failure of importance sampling for systems with a complex action. An alternative to evade the sign problem is quantum simulation. Although still in its infancy, a lot of progress has been made in devising algorithms to address these problems. In particular, recent efforts have addressed the question of how to produce thermal Gibbs states on a quantum computer. In this study, we apply a variational quantum algorithm to a low-dimensional model which has a local abelian gauge symmetry. We demonstrate how this approach can be applied to obtain information regarding the phase diagram as well as unequal-time correlation functions at non-zero temperature.
We derive the primitive quantum gate sets to simulate lattice quantum chromodynamics (LQCD) in the strong-coupling limit with one flavor of massless staggered quarks. This theory is of interest for studies at non-zero density as the sign problem can be overcome using Monte Carlo methods. In this work, we use it as a testing ground for quantum simulations. The key point is that no truncation of the bosonic Hilbert space is necessary as the theory is formulated in terms of color-singlet degrees of freedom (“baryons” and “mesons”). The baryons become static in the limit of continuous time and decouple, whereas the dynamics of the mesonic theory involves two qubits per lattice site. Lending dynamics also to the “baryons” simply requires to use the derived gate set in its controlled version.