We study electron-positron pair creation from the Dirac vacuum induced by a strong and slowly varying electric field (Schwinger effect) which is superimposed weak rapidly changing electromagnetic (dynamical creation). In subcritical regime where both mechanisms separately are strongly suppressed, their combined impact yields rate dramatically enhanced. Intuitively speaking, lowers threshold for dynamical particle creation--or, alternatively, fast generates additional seeds Schwinger...

We relate quark confinement, as measured by the Polyakov-loop order parameter, to colour described Kugo–Ojima/Gribov–Zwanziger scenario. identify a simple criterion for confinement based on IR behaviour of ghost and gluon propagators, compute order-parameter potential from knowledge Landau-gauge correlation functions with aid functional RG. Our approach predicts deconfinement transition in quenched QCD be first SU(3) second SU(2) – agreement general expectations. As an estimate critical...

Asymptotic safety is a theoretical proposal for the ultraviolet completion of quantum field theories, in particular gravity. Significant progress on this program has led to first characterization Reuter fixed point. Further advancement our understanding nature spacetime requires addressing number open questions and challenges. Here, we aim at providing critical reflection state art asymptotic program, specifying elaborating both technical conceptual nature. We also point out systematic...

Abstract We investigate nonperturbative aspects of the interplay chiral transitions in standard model course renormalization flow. focus on symmetry breaking mechanisms provided by QCD and electroweak sectors, latter which we a Higgs-top-bottom Yukawa theory. The becomes quantitatively accessible accounting for fluctuation-induced mixing Higgs field with mesonic composite fields QCD. In fact, our approach uses dynamical bosonization treats these scalar same footing. Varying scale relative to...

In a previous paper [G. V. Dunne and C. Schubert, Phys. Rev. D 72, 105004 (2005).], it was shown that the worldline expression for nonperturbative imaginary part of QED effective action can be approximated by contribution special closed classical path in Euclidean spacetime, known as instanton. Here we extend this formalism to compute also prefactor arising from quantum fluctuations about path. We present direct numerical approach determining prefactor, find simple explicit formula cases...

A renormalization group flow equation with a scale-dependent transformation of field variables gives unified description fundamental and composite degrees freedom. In the context effective average action, we study scalar bound states which are formed out fermions. We use gauged Nambu--Jona-Lasinio model at weak gauge coupling as an example. Thereby, notions state or particle become scale dependent, being classified by fixed-point structure couplings.

We investigate electron-positron pair production from vacuum for short laser pulses with a subcycle structure, in the nonperturbative regime (Schwinger production). use nonequilibrium quantum kinetic approach and show that momentum spectrum of created pairs is extremely sensitive to dynamics---depending on frequency $\ensuremath{\omega}$, pulse length $\ensuremath{\tau}$, carrier phase $\ensuremath{\phi}$---and shows several distinctive new signatures. This observation could not only help...

We propose a new catalysis mechanism for nonperturbative vacuum electron-positron pair production, by superimposing plane-wave x-ray probe beam with strongly focused optical laser pulse, such as is planned at the Extreme Light Infrastructure (ELI) facility. compute absorption coefficient arising from polarization effects photons below threshold in strong electric field. This setup should facilitate (first) observation of this QED effect light sources ELI yielding an envisioned intensity...

We compute Casimir interaction energies for the sphere-plate and cylinder-plate configuration induced by scalar-field fluctuations with Dirichlet boundary conditions. Based on a high-precision calculation using worldline numerics, we quantitatively determine validity bounds of proximity force approximation (PFA) which comparison between all corresponding experiments theory are based. observe quantitative failure PFA 1% level curvature parameter a/R > 0.00755. Even qualitatively, fails to...

The nonperturbative electron-positron pair production (Schwinger effect) is considered for space- and time-dependent electric fields $\stackrel{\ensuremath{\rightarrow}}{E}(\stackrel{\ensuremath{\rightarrow}}{x},t)$. Based on the Dirac-Heisenberg-Wigner formalism, we derive a system of partial differential equations infinite order 16 irreducible components Wigner function. In limit spatially homogeneous Vlasov equation quantum kinetic theory rediscovered. It shown that formalism can be...

Weinberg's asymptotic safety scenario provides an elegant mechanism to construct a quantum theory of gravity within the framework field based on non-Gaussian fixed point renormalization group flow. In this work we report novel evidence for validity scenario, using functional techniques determine flow Einstein-Hilbert action supplemented by two-loop counterterm found Goroff and Sagnotti. The resulting system beta functions comprises three scale-dependent coupling constants exhibits which...

Recently, the laser experiments BMV and GammeV, searching for light shining through walls, have published data calculated new limits on allowed masses couplings axionlike particles. In this paper we point out that these can serve to constrain a much wider variety of hidden-sector particles such as, e.g., minicharged photons. The improve existing bounds from older BFRT experiment by factor 2. Moreover, use PVLAS constraints possible rotation ellipticity after it has passed strong magnetic...

We study the impact of quantum gravity, formulated as a field theory metric, on chiral symmetry in fermionic matter sector. Specifically we address question whether metric fluctuations can induce breaking and bound state formation. Our results based functional renormalization group indicate that is left intact even at strong gravitational coupling. In particular, found asymptotically safe gravity where couplings approach non-Gaußian fixed point generically admits universes with light...

We compute the ghost anomalous dimension within asymptotic-safety scenario for quantum gravity. For a class of covariant gauge fixings and using functional renormalization group scheme, ${\ensuremath{\eta}}_{c}$ is negative, implying an improved UV behavior fluctuations. At non-Gaussian fixed point, we observe maximum value ${\ensuremath{\eta}}_{c}\ensuremath{\simeq}\ensuremath{-}0.78$ Landau-deWitt given scheme truncation. Most importantly, backreaction flow onto Einstein-Hilbert sector...

We critically examine the gauge, and field-parametrization dependence of renormalization group flows in vicinity non-Gau\ss{}ian fixed points quantum gravity. While physical observables are independent such calculational specifications, construction gravity field theories typically relies on off-shell quantities as $\beta$ functions generating functionals thus face potential stability issues with regard to generalized parametrizations. analyze a two-parameter class covariant gauge...

Nonperturbative electron-positron pair creation (the Schwinger effect) is studied based on the Dirac-Heisenberg-Wigner formalism in $1+1$ dimensions. An ab initio calculation of effect presence a simple space- and time-dependent electric field pulse performed for first time, allowing time evolution observable quantities such as charge density, particle number density or total created particles. We predict new self-bunching charges phase space due to spatial temporal structure pulse.

We use the Gross-Neveu model in $2<d<4$ as a simple fermionic example for Weinberg's asymptotic safety scenario: despite being perturbatively nonrenormalizable, defines an interacting quantum field theory valid to arbitrarily high momentum scales owing existence of non-Gaussian fixed point. Using functional renormalization group, we study uv behavior both purely well partially bosonized language. show that is realized at points formulations, universal critical exponents which determine...

We study the effective interactions of external electromagnetic fields induced by fluctuations virtual particles in vacuum quantum electrodynamics. Our main focus is on these at two-loop order. discuss detail emergence renowned Heisenberg-Euler action from underlying microscopic theory electrodynamics, emphasizing its distinction a standard one-particle irre-ducible action. In our explicit calculations we limit ourselves to constant and slowly varying fields, allowing us adopt locally field...

We present improved worldline numerical algorithms for high-precision calculations of Casimir interaction energies induced by scalar-field fluctuations with Dirichlet boundary conditions various geometries. Significant reduction cost is gained exploiting the symmetries ensemble in combination those configurations. This facilitates on standard PCs or small clusters. illustrate our strategies using experimentally most relevant sphere-plate and cylinder-plate configuration. compute curvature...