2,249 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
Renormalized Finite Temperature phi^4 theory from the 2PI Effective Action
We present an analytical and numerical study of scalar phi^4 theory at finite
temperature with a renormalized 2-loop truncation of the 2PI effective action.Comment: 4 pages. Presented at International Conference on Strong and
Electroweak Matter (SEWM 2006), Upton, New York, 10-13 May 200
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
Perturbative and Nonperturbative Kolmogorov Turbulence in a Gluon Plasma
In numerical simulations of nonabelian plasma instabilities in the hard-loop
approximation, a turbulent spectrum has been observed that is characterized by
a phase-space density of particles with exponent , which is larger than expected from relativistic
scatterings. Using the approach of Zakharov, L'vov and Falkovich, we analyse
possible Kolmogorov coefficients for relativistic -particle
processes, which give at most perturbatively for an energy cascade.
We discuss nonperturbative scenarios which lead to larger values. As an extreme
limit we find the result generically in an inherently nonperturbative
effective field theory situation, which coincides with results obtained by
Berges et al.\ in large- scalar field theory. If we instead assume that
scaling behavior is determined by Schwinger-Dyson resummations such that the
different scaling of bare and dressed vertices matters, we find that
intermediate values are possible. We present one simple scenario which would
single out .Comment: published versio
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
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
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
Bosonic effective action for interacting fermions
We compare different versions of a bosonic description for systems of
interacting fermions, with particular emphasis on the free energy functional.
The bosonic effective action makes the issue of symmetries particularly
transparent and we present for the Hubbard model an exact mapping between
repulsive and attractive interactions. A systematic expansion for the bosonic
effective action starts with a solution to the lowest order Schwinger-Dyson or
gap equation. We propose a two particle irreducible formulation of an exact
functional renormalization group equation for computations beyond leading
order. On this basis we suggest a renormalized gap equation. This approach is
compared with functional renormalization in a partially bosonized setting.Comment: new sections on exact mapping between attractive and repulsive
Hubbard model and relation between two-particle-irreducible formalism, 32
pages,1 figure,LaTe
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