1,682 research outputs found
Renormalized thermodynamics from the 2PI effective action
High-temperature resummed perturbation theory is plagued by poor convergence
properties. The problem appears for theories with bosonic field content such as
QCD, QED or scalar theories. We calculate the pressure as well as other
thermodynamic quantities at high temperature for a scalar one-component field
theory, solving a three-loop 2PI effective action numerically without further
approximations. We present a detailed comparison with the two-loop
approximation. One observes a strongly improved convergence behavior as
compared to perturbative approaches. The renormalization employed in this work
extends previous prescriptions, and is sufficient to determine all counterterms
required for the theory in the symmetric as well as the spontaneously broken
phase.Comment: 20 pages, 7 figures; PRD version, references added, very minor
change
2PI effective action for gauge theories: Renormalization
We discuss the application of two-particle-irreducible (2PI) functional
techniques to gauge theories, focusing on the issue of non-perturbative
renormalization. In particular, we show how to renormalize the photon and
fermion propagators of QED obtained from a systematic loop expansion of the 2PI
effective action. At any finite order, this implies introducing new
counterterms as compared to the usual ones in perturbation theory. We show that
these new counterterms are consistent with the 2PI Ward identities and are
systematically of higher order than the approximation order, which guarantees
the convergence of the approximation scheme. Our analysis can be applied to any
theory with linearly realized gauge symmetry. This is for instance the case of
QCD quantized in the background field gauge.Comment: 21 pages, 8 figures. Uses JHEP3.cl
Path integral quantization of scalar fluctuations above a kink
We quantize scalar fluctuations in 1+1 dimensions above a classical
background kink. The properties of the effective action for the corresponding
classical field are studied with an exact functional method, alternative to
exact Wilsonian renormalization, where the running parameter is a bare mass,
and the regulator of the quantum theory is fixed. We extend this approach, in
an appendix, to a Yukawa interaction in higher dimension.Comment: Comments adde
Numerically Exact Long Time Behavior of Nonequilibrium Quantum Impurity Models
A Monte Carlo sampling of diagrammatic corrections to the non-crossing
approximation is shown to provide numerically exact estimates of the long-time
dynamics and steady state properties of nonequilibrium quantum impurity models.
This `bold' expansion converges uniformly in time and significantly ameliorates
the sign problem that has heretofore limited the power of real-time Monte Carlo
approaches to strongly interacting real-time quantum problems. The new approach
enables the study of previously intractable problems ranging from generic long
time nonequilibrium transport characteristics in systems with large onsite
repulsion to the direct description of spectral functions on the real frequency
axis in Dynamical Mean Field Theory
Cell death and degeneration in the symbiotic dinoflagellates of the coral Stylophora pistillata during bleaching
Rising sea temperatures are increasing the incidences of mass coral bleaching (the dissociation
of the coralâalgal symbiosis) and coral mortality. In this study, the effects of bleaching
(induced by elevated light and temperature) on the condition of symbiotic dinoflagellates (Symbiodinium
sp.) within the tissue of the hard coral Stylophora pistillata (Esper) were assessed using a suite
of techniques. Bleaching of S. pistillata was accompanied by declines in the maximum potential
quantum yield of photosynthesis (Fv/Fm, measured using pulse amplitude modulated [PAM] fluorometry),
an increase in the number of Sytox-green-stained algae (indicating compromised algal membrane
integrity and cell death), an increase in 2â,7â-dichlorodihydrofluroscein diacetate (H2DCFDA)-
stained algae (indicating increased oxidative stress), as well as ultrastructural changes (vacuolisation,
losses of chlorophyll, and an increase in accumulation bodies). Algae expelled from S. pistillata
exhibited a complete disorganisation of cellular contents; expelled cells contained only amorphous
material. In situ samples taken during a natural mass coral bleaching event on the Great Barrier Reef
in February 2002 also revealed a high number of Sytox-labelled algae cells in symbio. Dinoflagellate\ud
degeneration during bleaching seems to be similar to the changes resulting from senescence-phase
cell death in cultured algae. These data support a role for oxidative stress in the mechanism of coral
bleaching and highlight the importance of algal degeneration during the bleaching of a reef coral
2PI Effective Action and Evolution Equations of N = 4 super Yang-Mills
We employ nPI effective action techniques to study N = 4 super Yang-Mills,
and write down the 2PI effective action of the theory. We also supply the
evolution equations of two-point correlators within the theory.Comment: 16 pages, 6 figures. Figure 2 replaced, approximation scheme
clarified, references adde
A unified picture of ferromagnetism, quasi-long range order and criticality in random field models
By applying the recently developed nonperturbative functional renormalization
group (FRG) approach, we study the interplay between ferromagnetism, quasi-long
range order (QLRO) and criticality in the -dimensional random field O(N)
model in the whole (, ) diagram. Even though the "dimensional reduction"
property breaks down below some critical line, the topology of the phase
diagram is found similar to that of the pure O(N) model, with however no
equivalent of the Kosterlitz-Thouless transition. In addition, we obtain that
QLRO, namely a topologically ordered "Bragg glass" phase, is absent in the
3--dimensional random field XY model. The nonperturbative results are
supplemented by a perturbative FRG analysis to two loops around .Comment: 4 pages, 4 figure
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