119252029
BPHZ renormalization and its application to non-commutative field theory
In a recent work a modified BPHZ scheme has been introduced and applied to one-loop Feynman graphs in non-commutative ϕ4-theory. In the present paper, we first review the BPHZ method and then we apply the modified BPHZ scheme as well as Zimmermann’s forest formula to the sunrise graph, i.e. a typical higher-loop graph involving overlapping divergences. Furthermore, we show that the application of the modified BPHZ scheme to the IR-singularities appearing in non-planar graphs (UV/IR mixing problem) leads to the introduction of a 1/p2 term and thereby to a renormalizable model. Finally, we address the application of this approach to gauge field theories.
16216330
A vector supersymmetry in noncommutative U(1) gauge theory with the Slavnov term
We consider noncommutative U(1) gauge theory with the additional term, involving a scalar field λ, introduced by Slavnov in order to cure the infrared problem. We show that this theory, with an appropriate space-like axial gauge-fixing, exhibits a linear vector supersymmetry similar to the one present in the 2-dimensional BF model. This vector supersymmetry implies that all loop corrections are independent of the λAA-vertex and thereby explains why Slavnov found a finite model for the same gauge-fixing.
1425207
Divergences in non-commutative gauge theories with the Slavnov term
The divergence structure of non-commutative gauge field theories (NCGFT) with a Slavnov extension [1],[2] is examined at one-loop level with main focus on the gauge boson self-energy. Using an interpolating gauge we show that even with this extension the quadratic IR divergence of the gauge boson self-energy is independent from a covariant gauge fixing as well as from an axial gauge. The proposal of Slavnov is based on the fact that the photon propagator shows a new transversality condition with respect to the IR dangerous terms. This novel transversality is implemented with the help of a new dynamical multiplier field. However, one expects that in physical observables such contributions disappear. A further new feature is the existence of new UV divergences compatible with the gauge invariance (BRST symmetry). We then examine two explicit models with couplings to fermions and scalar fields.
119279267
On non-commutative U⋆(1) gauge models and renormalizability
Based on our recent findings regarding (non-)renormalizability of non-commutative U(1) gauge theories [1, 2] we present the construction of a new type of model. By introducing a soft-breaking term in such a way that only the bilinear part of the action is modified, no interaction between the gauge sector and auxiliary fields occurs. Demanding in addition that the latter form BRST doublet structures, this leads to a minimally altered non-commutative U(1) gauge model featuring an IR damping behavior. Moreover, the new breaking term is shown to provide the necessary structure in order to absorb the inevitable quadratic IR divergences appearing at one-loop level in theories of this kind. In this paper we compute Feynman rules, symmetries and results for the vacuum polarization together with the one-loop renormalization of the gauge boson propagator and three-point functions.
18811875
Quantum Corrections for Translation-Invariant Renormalizable Non-Commutative Phi**4 Theory
In this paper we elaborate on the translation-invariant renormalizable 4 theory in 4-dimensional non-commu\-ta\-tive space which was recently introduced by the Orsay group. By explicitly performing Feynman graph calculations at one loop and higher orders we illustrate the mechanism which overcomes the UV/IR mixing problem and ultimately leads to a renormalizable model. The obtained results show that the IR divergences are also suppressed in the massless case, which is of importance for the gauge field theoretic generalization of the scalar field model.
118634727
Loop calculations for the non-commutative U⋆(1) gauge field model with oscillator term
Motivated by the success of the non-commutative scalar Grosse–Wulkenhaar model, a non-commutative U⋆(1) gauge field theory including an oscillator-like term in the action has been put forward in (Blaschke et al. in Europhys. Lett. 79:61002, 2007). The aim of the current work is to analyze whether that action can lead to a fully renormalizable gauge model on non-commutative Euclidean space. In a first step, explicit one-loop graph computations are hence presented, and their results as well as necessary modifications of the action are successively discussed.
119225239
Quarkonia and QGP studies
We summarize results of recent studies of heavy quarkonia correlators and spectral functions at finite temperatures from lattice QCD and systematic T-matrix studies using QCD motivated finite-temperature potentials. We argue that heavy quarkonia dissociation shall occur in the temperature range 1.2 ⩽ T d / T c ⩽ 1.5 by the interplay of both screening and absorption in the strongly correlated plasma medium. We discuss these effects on the quantum mechanical evolution of quarkonia states within a time-dependent harmonic oscillator model with complex oscillator strength and compare the results with data for R A A / R A A C N M from RHIC and SPS experiments. We speculate whether the suppression pattern of the rather precise NA60 data from In-In collisions may be related to the recently discovered X(3872) state. Theoretical support for this hypothesis comes from the cluster expansion of the plasma Hamiltonian for heavy quarkonia in a strongly correlated medium.
119222844
Kinetics of Photon Radiation off an e–e+-Plasma Created from the Vacuum in a Strong Laser Field
We consider the one-photon annihilation mechanism in a electron - positron quasiparticle plasma (EPP) created from the vacuum in a strong subcritical laser field due to the dynamical Schwinger mechanism. On the basis of a kinetic theory approach we show that the secondary photons have a radiation spectrum proportional to 1/k (flicker noise). This effect is very small for EPP excitations in the optical spectrum but can reach quite observable values in the γ -ray region (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
118701657
Photon cluster excitation mechanism in an e-e+ plasma created from vacuum by a strong electromagnetic field
In the low density approximation of nonperturbative kinetic theory we investigate the vacuum creation of an electron-positron plasma (EPP) under the action of an external monochromatic "laser" electric field with the focus on multiphoton processes. We analyse in some detail the role of the photon cluster mechanism of EPP excitation and show that this mechanism plays the dominating role in the case when a large photon number from the external field reservoir takes part in the breakdown of the energy gap. We obtain the distribution function in this approximation and discuss its properties.
119255005
Cluster-virial expansion for nuclear matter within a quasiparticle statistical approach
Abstract Correlations in interacting many-particle systems can lead to the formation of clusters, in particular bound states and resonances. Systematic quantum statistical approaches allow to combine the nuclear statistical equilibrium description (law of mass action) with mean-field concepts. A chemical picture, which treats the clusters as distinct entities, serves as an intuitive concept to treat the low-density limit. Within a generalized Beth–Uhlenbeck approach, the quasiparticle-virial expansion is extended to include arbitrary clusters, where special attention must be paid to avoid inconsistencies such as double counting. Correlations are suppressed with increasing density due to Pauli blocking. The contribution of the continuum to the virial coefficients can be reduced by considering clusters explicitly and introducing quasiparticle energies. The cluster-virial expansion for nuclear matter joins known benchmarks at low densities with those near saturation density.
1436262
Exploring the QCD phase diagram with compact stars
We investigate a nonlocal chiral quark model with separable 4-fermion interaction for the case of U (3) flavor symmetry and show that strange quark matter is unlikely to occur in a large enough volume of a compact star to entail remarkable observational consequences. The phase diagram in the two-flavor sector of such model has a critical end point of the line of first order chiral/deconfinement phase transitions on which a triple point marks the junction with the critical line for second order phase transitions to two-flavor color superconductivity (2SC) below T ∼ 80 MeV. Stable hybrid star configurations with large quark matter core in a color superconducting phase can exist. A consistent cooling phenomenology requires that all quark species be gapped, the minimal pairing gap of the order of 10 – 100 keV.