Academic literature on the topic 'Cosmological reheating'

Quantum fluctuation of unstable modes about gravitational instantons causes the instability of flat space at finite temperature, leading to the spontaneous process of nucleating quantum black holes. The energy-density of quantum black holes, depending on the initial temperature, gives the cosmological term, which naturally accounts for the inflationary phase of the early universe. The reheating phase is attributed to the Hawking radiation and annihilation of these quantum black holes. Then, the radiation energy-density dominates over the energy-density of quantum black holes, the universe started the standard cosmology phase. In this phase the energy-density of quantum black holes depends on the reheating temperature. It asymptotically approaches to the cosmological constant in matter domination phase, consistently with current observations.

Abstract We present a cosmological model of an early-time scenario that incorporates a relaxation process of the would-be large vacuum energy, followed by a reheating era connecting to the standard hot big bang universe. Avoiding fine-tuning the cosmological constant is achieved by the dynamics of a scalar field whose kinetic term is modulated by an inverse power of spacetime curvature [1,2]. While it is at work against radiative corrections to the dark energy, this mechanism alone would wipe out not only the vacuum energy but also all other matter contents. Our present work aims to complete the scenario by exploiting a null-energy-condition violating sector whose energy is eventually transferred to a reheating sector. We provide an explicit example of this process and thus a concrete scenario of the cosmic onset that realizes the thermal history of the Universe with a negligible cosmological constant.

Abstract We study reheating of inflationary models with general non-minimal coupling K(ϕ)R with K(ϕ) ∼ √(V(ϕ)) where R is the Ricci scalar and R is the inflaton potential. In particular, when we take the monomial potential K(ϕ) ∝ ϕ m with m∈ℤ+, we provide general analytic expressions for cosmological observables. We consider a wide range of non-minimal coupling ξ∈[0,∞) in metric and Palatini formalisms and derive the predictions for cosmological observables and the reheating temperature taking a general equation of state parameter w reh.

The end of inflation is connected to the standard cosmological scenario through reheating. During reheating, the inflaton oscillates around the minimum of the potential and thus decays into the daughter particles that populate the Universe at later times. Using cosmological evolution for observable CMB scales from the time of Hubble crossing to the present time, we translate the constraint on the spectral index [Formula: see text] from Planck data to the constraint on the reheating scenario in the context of Kähler moduli inflation. We find that the equation of state parameter plays a crucial role in the reheating analysis, however the details of the one parameter potential are irrelevant if the analysis is done strictly within the slow-roll formalism. In addition, we extend the de facto analysis generally done only for the pivot scale to all the observable scales which crossed the Hubble radius during inflation, where we study how the maximum number of e-folds varies for different scales, and the effect of the equation of state and potential parameters.

Abstract We present a simple procedure to obtain universal bounds for quantities of cosmological interest, such as the number of e-folds during inflation, reheating, and radiation, as well as the reheating temperature. The main assumption is to represent each of the various epochs of evolution of the universe as being due to a single substance changing instantaneously into the next, describing a new era of evolution of the universe. This assumption, commonly used to obtain solutions of the Friedmann equations for simple cosmological models, is implemented here to find model-independent bounds on cosmological quantities of interest. In particular, we find that the bound Nk ≈ 56 for -1/3 < ω re < 1/3 is very robust as an upper bound on the number of e-folds during inflation and also as a lower bound when ω re > 1/3, where ω re is the effective equation of state parameter during reheating. These are model-independent results that any single-field model of inflation should satisfy. As an example we illustrate with the basic α attractor model the usual model dependent approach, and the one presented here, and show how they complement each other.

The reheating era after inflation is analyzed in the framework of the braneworld models. We study reheating by calculating the reheating temperature in a braneworld inflation for various cosmological parameters. The variation of reheating [Formula: see text]-folding number and reheating temperature were obtained and analyzed as function of a spectrum of perturbation for a polynomial potential [Formula: see text]. We have applied the slow-roll approximation in the high energy limit to constraint the parameter potentials by confronting our results to recent Planck 2018 observations. We have shown that in general the best values of the predicted reheating temperature is of the order [Formula: see text] GeV, with a brane tension [Formula: see text] GeV4. We have also shown that the polynomial potential in the case [Formula: see text] provides the best fit results with recent observational constraints.

Cold-atom quantum simulators offer unique possibilities to prepare, manipulate, and probe quantum many-body systems. However, despite the high level of control in modern experiments, not all observables of interest are easily accessible. This thesis aims at establishing protocols to measure currently elusive static and dynamic properties of quantum systems. The experimental feasibility of these schemes is illustrated by means of numerical simulations for relevant applications in many-body physics and quantum simulation. In particular, we introduce a general method for measuring dynamical correlations based on non-Hermitian linear response. This enables unbiased tests of the famous fluctuation-dissipation relation as a probe of thermalization in isolated quantum systems. Furthermore, we develop ancilla-based techniques for the measurement of currents and current correlations, permitting the characterization of strongly correlated quantum matter. Another application is geared towards revealing signatures of supersolidity in spin-orbit-coupled Bose gases by exciting the relevant Goldstone modes. Finally, we explore a scenario for quantum-simulating post-inflationary reheating dynamics by parametrically driving a Bose gas into the regime of universal far-from-equilibrium dynamics. The presented protocols also apply to other analog quantum simulation platforms and thus open up promising applications in the field of quantum science and technology.
I simulatori quantistici ad atomi freddi offrono possibilità uniche per preparare, manipolare e sondare sistemi quantistici a molti corpi. Tuttavia, nonostante l'alto livello di controllo raggiunto negli esperimenti moderni, non tutte le osservabili di interesse sono facilmente accessibili. Lo scopo di questa tesi è quello di stabilire protocolli per misurare delle proprietà statiche e dinamiche dei sistemi quantistici attualmente inaccessibili. La fattibilità sperimentale di questi schemi è illustrata mediante simulazioni numeriche per applicazioni rilevanti nella fisica a molti corpi e nella simulazione quantistica. In particolare, introduciamo un metodo generale per misurare le correlazioni dinamiche basato su una risposta lineare non hermitiana. Ciò consente test imparziali della famosa relazione fluttuazione-dissipazione come sonda di termalizzazione in sistemi quantistici isolati. Inoltre, sviluppiamo tecniche basate su ancilla per la misura di correnti e correlazioni di corrente, consentendo la caratterizzazione della materia quantistica fortemente correlata. Un'altra applicazione è orientata a rivelare l'impronta della supersolidità nei gas Bose con accoppiamento spin-orbita eccitando il corrispondente modo di Goldstone. Infine, esploriamo uno scenario per la simulazione quantistica della dinamica di riscaldamento post-inflazione modulando parametricamente un gas Bose e portandolo nel regime della dinamica universale lontana dall'equilibrio. I protocolli presentati si applicano anche ad altre piattaforme di simulazione quantistica analogica e aprono quindi applicazioni promettenti nel campo della scienza e della tecnologia quantistica.
Quantensimulatoren auf Basis ultrakalter Atome eröffnen einzigartige Möglichkeiten zur Präparation, Manipulation und Untersuchung von Quanten-Vielteilchen-Systemen. Trotz des hohen Maßes an Kontrolle in modernen Experimenten sind jedoch nicht alle interessanten Observablen auf einfache Weise zugänglich. Ziel dieser Arbeit ist es, Protokolle zur Messung aktuell nur schwer erfassbarer statischer und dynamischer Eigenschaften von Quantensystemen zu etablieren. Die experimentelle Realisierbarkeit dieser Verfahren wird durch numerische Simulationen anhand relevanter Anwendungen in der Vielteilchenphysik und Quantensimulation veranschaulicht. Insbesondere wird eine allgemeine Methode zur Messung dynamischer Korrelationen basierend auf der linearen Antwort auf nicht-hermitesche Störungen vorgestellt. Diese ermöglicht unabhängige Tests des berühmten Fluktuations-Dissipations-Theorems als Indikator der Thermalisierung isolierter Quantensysteme. Darüber hinaus werden Verfahren zur Messung von Strömen und Strom-Korrelationen mittels Kopplung an einen Hilfszustand entwickelt, welche die Charakterisierung stark korrelierter Quantenmaterie erlauben. Eine weitere Anwendung zielt auf die Enthüllung spezifischer Merkmale von Supersolidität in Spin-Bahn-gekoppelten Bose-Einstein-Kondensaten ab, indem die relevanten Goldstone-Moden angeregt werden. Schließlich wird ein Szenario zur Quantensimulation post-inflationärer Thermalisierungsdynamik durch die parametrische Anregung eines Bose-Gases in das Regime universeller Dynamik fern des Gleichgewichts erschlossen. Die dargestellten Protokolle lassen sich auch auf andere Plattformen für analoge Quantensimulation übertragen und eröffnen damit vielversprechende Anwendungen auf dem Gebiet der Quantentechnologie.

One of the most interesting and at the same time complex problems of modern physics is to determine how does the past and the future of our Universe look like. Especially, we are interested in the first moments of its history as they are beyond our experimental reach at present but they influence later stages of the evolution of the Universe we are able to observe. Generally accepted cosmological scenario starts with the Big Bang, we speculate that theUniverse was homogeneous and isotropic with very high temperature and pressure at the beginning, after which our Universe starts to gradually cool down and expand ending up as the Universe we live in. We assume that very early in the evolution of the Universe the process of exponential expansion occurred which we call inflation. During this period density fluctuations were amplified giving the origin to the seeds that would form all the large scalestructure in the Universe – stars, galaxies etc. After inflation we distinguish two periods important for the presented research – preheating and reheating, during which out of the inflaton – the field that drives inflation, elementary particles that fill the Universe now were produced.The thesis describes the processes of cosmological particle production in the timedependent theories and it focuses on three main subjects: gravitational reheating with an instant period of particle creation, multi-stages non-perturbative production in both adiabatic approximation and interacting theory. All of them are based on the fact that the vacuum state changes in time and that in the parameter space there exist a region where particle production is energetically favourable and efficient enough to be observed.In the chapter concerning gravitational reheating particles are produced solely due to the change in the evolution of the observed Universe in time, which is described by the scale factor that depends on time. In our research we assume this kind of particle production right after the end of inflation in a very general way. From our analysis we can draw generic conclusions about available observables involving the features of inflation, observed spectrum of gravitational waves and even characteristics of dark matter or dark energy.The main part of the thesis concentrates on the general description of the multiphase non-perturbative production of particles, especially in case of inflation. The essence of my research in this matter lies in the fact that production of particles can repeat itself until it is energetically possible and the previous stage can affect the next one. We investigate the role of the masses of particles and values of couplings in various scenarios motivated by the usual cosmological considerations with and without supersymmetry. In addition, we focus on the role of light states in the theory proving that in general even massless states not coupled to inflaton can be efficiently produced due to effects of quantum physics and also that additional light sector present in the theory can quench the production after inflation completely due to backreaction.
Jednym z najciekawszych i jednocześnie najbardziej złożonych problemów współczesnej fizyki jest ustalenie, jak wygląda przeszłość i przyszłość Wszechświata. Szczególnie interesuje nas jego wczesna ewolucja, ponieważ znajduje się ona obecnie poza naszym zasięgiem eksperymentalnym, ale wpływa na późniejszą historię Wszechświata, którą już możemy obserwować. Ogólnie przyjęty model kosmologiczny zaczyna się od WielkiegoWybuchu i zakłada, że Wszechświat na początku był jednorodny i izotropowy z bardzo wysoką temperaturą i ciśnieniem, po czym zaczął stopniowo się ochładzać i rozszerzać, kończąc jako Wszechświat, w którym żyjemy. Poza tym zakłada się, że bardzo wcześnie w ewolucji Wszechświata nastąpił proces eksponencjalnego rozszerzania się, który nazywamy inflacją i w którym fluktuacje gęstości zostały wzmocnione, dając początek wszystkim strukturom wielkoskalowym - gwiazdom, galaktykom itp. Po zakończeniu inflacji miały miejsce dwa procesy bardzo istotne dla przedstawionych badań – reheating i preheating, podczas których z inflatonu, czyli pola napędzającego inflacje, powstały cząstki elementarne obecnie wypełniające Wszechświat.Rozprawa opisuje procesy kosmologicznej produkcji cząstek w teoriach zależnych od czasu i skupia się na trzech głównych tematach: grawitacyjny reheating z błyskawicznym procesem tworzenia cząstek oraz wieloetapowa i nieperturbacyjna produkcja zarówno w przybliżeniu adiabatycznym, jak i w teorii oddziałującej. Wszystkie opierają się na fakcie, że stan próżni zmienia się w czasie i że w przestrzeni parametrów istnieje obszar, w którymwytwarzanie cząstek jest energetycznie korzystne i wystarczająco wydajne, aby mogło nastąpić.W rozdziale dotyczącym reheatingu grawitacyjnego cząstki są wytwarzane wyłącznie ze względu na zmianę ewolucji obserwowanego Wszechświata w czasie opisywaną przez zależący od czasu czynnik skali. W naszych badaniach rozważamy w bardzo ogólny sposób tego rodzaju produkcję cząstek tuż po zakończeniu inflacji, co pozwala wyciągnąć ogólne wnioski na temat dostępnych obserwabli dotyczących inflacji, obserwowanego spektrum falgrawitacyjnych, a nawet własności ciemnej materii lub ciemnej energii.Główna cześć pracy koncentruje się na ogólnym opisie wielofazowej nieperturbacyjnej produkcji cząstek, w szczególności w przypadku inflacji. Istota tych badań polega na tym, że produkcja cząstek może się powtarzać dopóki jest dozwolona energetycznie, a poprzedni jej etap może wpłynąć na następny. Badamy rolę mas cząstek i wartości sprzężeń w rożnych scenariuszach motywowanych standardowymi rozważaniami kosmologicznymiz uwzględnieniem i bez supersymetrii. Ponadto koncentrujemy się na roli stanów bezmasowych w teorii, dowodząc, że nawet bezmasowe stany niesprzężone bezpośrednio z inflatonem mogą być produkowane ze względu na poprawki kwantowe, a także, że dodatkowy bezmasowy sektor może zatrzymać całkowicie produkcję po inflacji.

The theory of cosmological inflation, despite being widely accepted as the important ingredient of the concordance model of cosmology, suffers from a number of drawbacks and unresolved issues. In particular, it is still a very general concept and the relation of the inflaton field or fields with the standard model of particle physics remains unclear. Further theoretical inquiry, as well as improved measurements of cosmological parameters are needed to verify which, if any, model of inflation is realized in Nature. The results of our research presented herein are aimed at decreasing the uncertainty of interpretation of CMB observables with respect to the features of inflationary models by improving the knowledge about post-inflationary reheating era and checking the impact of geometrical destabilization of inflation on inflationary trajectory. This goal was realized through three distinct research objectives. The first one was the investigation of the plausibility of the self-resonance mechanism as reheating scenario in single-field inflationary models. Our investigation showed that self-resonance reheating is very rare among inflationary models. Out of 52 models, which we investigated, barring the already known example of single-field α-attractors T-models, we selected only one - KKLT inflationary model - characterized by effective parametric resonance reheating. The second objective of our research was the analysis of parametric resonance reheating in α-attractor T-models of inflation. We showed that near the end of inflation the initially stable second field present in these models become tachyonic and is destabilized. We found that taking this fact into account may strongly speed up reheating compared to the previous speculations, which we based on the single field approximations. For small values of the parameter α reheating can be almost instantaneous and complete within the fraction of an e-fold. The third research objective was the analysis how the mechanism of geometric destabilization may affect the inflationary trajectory. If we treat inflation as an effective field theory this mechanism emerge very naturally and seems to be quite generic. We found that it can significantly change the inflationary trajectory and results in the prolonged period of inflation. In this way the geometrical destabilization may change the cosmological predictions of the inflationary models.

A comprehensive and detailed account of the physics of gravitational waves and their role in astrophysics and cosmology. The part on astrophysical sources of gravitational waves includes chapters on GWs from supernovae, neutron stars (neutron star normal modes, CFS instability, r-modes), black-hole perturbation theory (Regge-Wheeler and Zerilli equations, Teukoslky equation for rotating BHs, quasi-normal modes) coalescing compact binaries (effective one-body formalism, numerical relativity), discovery of gravitational waves at the advanced LIGO interferometers (discoveries of GW150914, GW151226, tests of general relativity, astrophysical implications), supermassive black holes (supermassive black-hole binaries, EMRI, relevance for LISA and pulsar timing arrays). The part on gravitational waves and cosmology include discussions of FRW cosmology, cosmological perturbation theory (helicity decomposition, scalar and tensor perturbations, Bardeen variables, power spectra, transfer functions for scalar and tensor modes), the effects of GWs on the Cosmic Microwave Background (ISW effect, CMB polarization, E and B modes), inflation (amplification of vacuum fluctuations, quantum fields in curved space, generation of scalar and tensor perturbations, Mukhanov-Sasaki equation,reheating, preheating), stochastic backgrounds of cosmological origin (phase transitions, cosmic strings, alternatives to inflation, bounds on primordial GWs) and search of stochastic backgrounds with Pulsar Timing Arrays (PTA).