Understanding the emergence of classical behavior from a quantum theory is vital to establishing origin for temperature fluctuations observed in cosmic microwave background. We show that real-space approach can comprehensively address quantum-to-classical transition problem leading order curvature perturbations. To this end, we test spatial bipartitions quadratic systems interplay between three different signatures behavior: (i) decoherence; (ii) peaking Wigner function about trajectories;...

We revisit particle creation in strong fields, and backreaction on those from an amplitudes perspective. describe the field by initial coherent state of photons which we explicitly evolve time, thus going beyond background-field approximation, then consider observables quantify effects backreaction. present expressions for waveform, vacuum persistence probability, number produced at next-to-leading order, all are impacted backreaction, along with statistics pairs. find that converting...

The presence of strong electromagnetic fields adds huge complexity to QED Feynman diagrams, such that new methods are required calculate higher-loop and higher-multiplicity scattering amplitudes. Here we use the worldline formalism present “master formulas” for all tree level amplitudes two massive particles an arbitrary number photons, in a plane wave background, both scalar spinor QED. is treated without approximation throughout, meaning particular our formulas valid strong-field regime...

We discuss several aspects of quantum field theory a scalar in Friedmann universe, clarifying and highlighting conceptual technical issues. (A) show that one can map the dynamics (1) massless universe with power law expansion to (2) massive de Sitter spacetime, which allows us understand features either system clarifies issues related limit. (B) obtain useful integral representation for Euclidean Green's function by relating it solution hypothetical electrostatic problem five dimensions....

A bstract We use the worldline formalism to derive Bern-Kosower type Master Formulae for tree-level scattering of a charged particle and an arbitrary number photons on impulsive PP-waves, where coupling PP-wave matter is treated fully non-perturbatively. show that, in certain kinematic regime characterised by semi-classical positive energy condition, both off-shell currents amplitudes exhibit two novel factorisation structures. First, they may be written as vacuum but with single additional...

Bouncing models are alternatives to inflationary cosmology that replace the initial Big-Bang singularity by a `bouncing' phase. A deeper understanding of conditions universe, in these scenarios, requires knowledge quantum aspects bouncing models. In this work, we propose two classes can be studied with great analytical ease and hence, provide test-bed for investigating more profound problems universes. Our model's key ingredients enable us do straightforward calculations: (i) convenient...

Abstract We consider the introduction of anisotropy in a class bouncing models cosmology. The presence often spells doom on models, since energy density due to anisotropic stress outweighs that other matter components, as universe contracts. Different suggestions have been made literature resolve this pathology, classically. Here, we introduce family which shear can be tuned either allow or forbid classical scenarios. Following which, show quantum cosmological considerations drastically...

We demonstrate that the positive frequency modes for a complex scalar field in constant electric (Schwinger modes), three different gauges, can be represented as exact Lorentzian worldline path integral amplitudes. Although mathematical forms of mode functions differ each gauge, we show simple prescription worldlines' boundary conditions dispenses Schwinger all gauges (that considered) unified manner. Following that, using our formalism, derive Bogoliubov coefficients and, hence, particle...

In flat spacetime, two inequivalent vacuum states that arise rather naturally are the Rindler |R〉 and Minkowski |M〉. We discuss several aspects of vacuum, concentrating on propagator Schwinger (heat) kernel defined using |R〉, both in Lorentzian Euclidean sectors. start by exploring an intriguing result due to Candelas Raine [J. Math. Phys. 17, 2101 (1976)], viz., GR, Feynman corresponding can be expressed as a curious integral transform GM, show this relation follows from well-known GM...

We consider a proposal to define the wave function of Universe as sum over spacetimes that eventually inflate. In minisuperspace model, we explicitly show simple family initial conditions, parametrized by positive real number ${a}_{0}$, can be imposed realize this prescription. The resulting is found proportional Hartle-Hawking and its dependence on ${a}_{0}$ only through an overall phase factor. Motivated observation, ask whether it possible analytically extend extended region...

We discuss several aspects of particle production in: (a) time dependent electric field and (b) expanding Friedmann background. In the first part paper, we provide an algebraic mapping between differential equations describing these two phenomena. This allows a direct comparison highlight interesting features both cases using this approach. determine form (equivalent) corresponding to different spacetimes discover, for example, time-dependent which, in specific limit, leads Planck's spectrum...

We propose that a quantum black hole can produce new kind of late-time gravitational echoes, facilitated by near-horizon process analogous to Andreev reflection in condensed matter systems. In comparison the traditional echo scenarios where region is treated as an ordinary reflector, we argue that, consequent scattering, this better described reflector. Such interactions lead novel contribution echoes with characteristic phase difference, effect which how reflections propagating particlelike...

A spatially homogeneous, time-dependent, electric field can produce charged particle pairs from the vacuum. When is constant, mean number of which are produced depends on and coupling constant in a non-analytic manner, showing that this result cannot be obtained standard perturbation theory quantum electrodynamics. varies with time vanishes asymptotically, may depend either analytically or non-analytically. We investigate nature dependence several specific contexts. show production for class...

In this work, we derive the asymptotic quasi-normal modes of a Banados–Teitelboim–Zanelli (BTZ) black hole using quantum field theoretic Lagrangian. The BTZ is very popular system in context 2 + 1-dimensional gravity. However, to our knowledge have been studied only classical domain. Here show way quantize by mapping it Bateman–Feschbach–Tikochinsky oscillator and Caldirola–Kanai oscillator. We also discussed couple other potentials which method can be applied.

We use the worldline formalism to derive Bern-Kosower type Master Formulae for tree-level scattering of a charged particle and an arbitrary number photons on impulsive PP-waves, where coupling PP-wave matter is treated fully non-perturbatively. show that, in certain kinematic regime characterised by semi-classical positive energy condition, both off-shell currents amplitudes exhibit two novel factorisation structures. First, they may be written as vacuum but with single additional photon,...

We revisit particle creation in strong fields, and backreaction on those from an amplitudes perspective. describe the field by initial coherent state of photons which we explicitly evolve time, thus going beyond background approximation, then consider observables quantify effects backreaction. present expressions for waveform, vacuum persistence probability, number produced at next-to-leading order, all are impacted backreaction, along with statistics pairs. find that converting between...

We consider the backreaction of a quantum system $q$ on an effectively classical degree freedom $C$ that is interacting with it. The equation based standard path integral formalism gives so-called `in-out' equation, which has several serious pathologies. One can use different prescription, referred to as `in-in' approach, resolves all issues equation. However, this procedure usually invoked in rather ad hoc manner. Here we provide rigorous derivation approach by exploiting concept evolution...

In recent years, significant progress has been made in the computation of conservative and dissipative scattering observables using post-Minkowskian approach to gravitational dynamics. However, for accurate modeling unbound orbits, an appropriate effective-one-body (EOB) resummation post-Minkowski results that also accounts dynamics is desirable. As a step this direction, we consider electromagnetic analog problem here. We show six-parameter equation motion encapsulates third order coupling...

Understanding the emergence of classical behavior from a quantum theory is vital to establishing origin for temperature fluctuations observed in Cosmic Microwave Background (CMB). We show that real-space approach can comprehensively address quantum-to-classical transition problem leading order curvature perturbations. To this end, we test spatial bipartitions quadratic systems interplay between three different signatures behavior: i) decoherence, ii) peaking Wigner function about...