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M. Faber

Publications and source records attributed to M. Faber.

104 records · Page 6Linked to original sources
arXiv1997

Nuclear aspects of the solar neutrino problem

The present status of the nuclear reaction rates determining the solar neutrino flux is discussed. This includes the reaction rates for the two branching ratios of the three pp-chains involving the reactions 3He(3He,2p)4He and 3He(4He,gamma)7Be for the first branching, and 7Be(e-,nu_e)7Li and 7Be(p,gamma)7B for the second branching. Mainly we will concentrate on the basic nuclear reaction p + p -> D + e+ + nu_e of the pp-chains. We use a relativistic field theory model of the deuteron to calculate the low-energy cross section for this reaction. The theoretical prediction of the cross section obtained is about 2.9 times largerthan given in the conventional potential approach. The consequences of this new reaction rate for the solar neutrino problem will be presented and discussed.

nucl-th↗
arXiv1997

On the solar neutrino problem in the relativistic field theory model of the deuteron

The relativistic field theory model of the deuteron suggested by us previously is applied to the calculation of the reaction rate of the low-energy two-proton fusion p + p -> D + e+ + nu. The theoretical prediction of the reaction rate obtained is 2.9 times larger than given by the potential approach. This leads to a strong suppression of the high energy solar neutrino fluxes.

astro-ph↗
arXiv1996

Domain walls, $Z(N)$ charge and $A_0$ condensate: a canonical ensemble study

The deconfinement phase transition is studied in the ensemble canonical with respect to triality. Since this ensemble implies a projection to the zero triality sector of the theory we introduce a quantity which is insensitive to $Z(N_c)$ symmetry but can reveal a critical behaviour in the theory with dynamical quarks. Further, we argue that in the canonical ensemble description of full QCD there exist domains of different $Z(N_c)$ phases which are degenerate and possess normal physical properties. This contradicts the predictions of the grand canonical ensemble. We propose a new order parameter to test the realization of the discrete $Z(N_c)$ symmetry at finite temperature and calculate it for the case of $Z(2)$ gauge fields coupled to fundamental fermions.

hep-lat↗
arXiv1996

Center Dominance and Z2 Vortices in SU(2) Lattice Gauge Theory

We find, in close analogy to abelian dominance in maximal abelian gauge, the phenomenon of center dominance in maximal center gauge for $SU(2)$ lattice gauge theory. Maximal center gauge is a gauge-fixing condition that preserves a residual $Z_2$ gauge symmetry; ``center projection'' is the projection of $SU(2)$ link variables onto $Z_2$ center elements, and ``center dominance'' is the fact that the center-projected link elements carry most of the information about the string tension of the full theory. We present numerical evidence that the thin $Z_2$ vortices of the projected configurations are associated with ``thick'' $Z_2$ vortices in the unprojected configurations. The evidence also suggests that the thick $Z_2$ vortices may play a significant role in the confinement process.

hep-lat↗
arXiv1996

Deconfinement in QCD with dynamical quarks

We study the phase structure of full QCD within the canonical ensemble with respect to triality in a lattice formulation. The procedure for the calculation of the effective potentials in this case is given. As an example we consider the three dimensional SU(2) gauge model at finite temperatures in the strong coupling region. The potential exhibits a deconfinement phase transition unlike the similar potential obtained in the grand canonical ensemble which demonstrates explicit Z(N) symmetry breaking at any temperature. Furthermore, we investigate the effective potential with the chiral condensate included. In contradiction to other authors, we find chiral symmetry restoration in all triality sectors. In the scheme with massless staggered fermions we observe chiral symmetry restoration accompanying a deconfinement phase transition of first order. Above the critical point, besides two Z(2) symmetric "deconfining" vacua there exists a metastable "confining" vacuum in a wide region of parameters. Such a picture could be interpreted as an indication on a mixed state of hadrons and quarks in the vicinity of the critical line.

hep-lat↗
arXiv1996

Casimir Scaling vs. Abelian Dominance in QCD String Formation

We show that the hypothesis of abelian dominance in maximal abelian gauge, which is known to work for Wilson loops in the fundamental representation, fails for Wilson loops in higher group representations. Monte Carlo simulations are performed on lattice $SU(2)$ gauge theory, in $D=3$ dimensions, in the maximal abelian gauge, in the confined phase. It is well-known that Creutz ratios extracted from loops in various group representations are proportional to the quadratic Casimir of each representation, in a distance interval from the confinement scale to the point where color screening sets in. In contrast we find numerically, in the same interval, that string tensions extracted from loops built from abelian projected configurations are the same for the fundamental and $j=3/2$ representations, and vanish for the adjoint representation. In addition, we perform a lattice Monte Carlo simulation of the Georgi-Glashow model in $D=3$ dimensions. We find that the representation-dependence of string tensions is that of pure Yang-Mills in the symmetric phase, but changes abruptly to equal tensions for the $j=1/2,~3/2$ representations, and zero tension for $j=1$, at the transition to the Higgs phase. Our results indicate that an effective abelian theory at the confinement scale, invoking {\it only} degrees of freedom (monopoles and photons) associated with a particular Cartan subalgebra, is inadequate to describe the actual interquark potential in an unbroken non-abelian gauge theory.

hep-lat↗
arXiv1995

Triality in QCD at Zero and Finite Temperature: A New Direction

Discrete symmetries in grand canonical ensembles and in ensembles canonical with respect to triality are investigated. We speculate about the general phase structure of finite temperature gauge theories with discrete $Z(N)$ symmetry. Low and high temperature phases turn out to be different in both ensembles even for infinite systems. It is argued that gauge theories with matter fields in the fundamental representation should be treated in ensembles canonical with respect to triality if one wants to avoid unphysical predictions. Further, we discuss as a physical consequence of such a treatment the impossibility of the existence of metastable phases in the quark-gluon plasma.

hep-ph↗
arXiv1994

Topological charge density around static colour sources in lattice QCD with dynamical quarks

We update our numerical investigation of topological structures around static quarks in pure gauge QCD by results of the first runs including dynamical quarks. Simulations were performed on an $8^3\times4$ lattice, with $SU(3)$ Wilson action, with 3 flavours of quarks of equal mass, both in the confinement and deconfinement phase. In the confinement phase we observe indications for the existence of a flux tube between a static quark and antiquark, flux-tube breaking for large separations, and local correlation between the topological charge density and chiral condensate. In the deconfinement phase almost all configurations turn out to be topologically trivial.

hep-lat↗
arXiv1994

Flux tubes and topological charges in finite-temperature lattice QCD

Topological properties of the vacuum were investigated in finite-temperature lattice QCD without and with dynamical quarks using a local operator of topological charge density and a variant of cooling. Below the deconfinement temperature evidence for flux tube formation was observed in the distribution of topological charge density around a static $Q\bar Q$ pair. With dynamical quarks, the flux tube breaks when the distance between the static quark and antiquark increases.

hep-lat↗
arXiv1993

Fresh look on triality

Investigating the $Z_3$ symmetry in Quantum Chromodynamics (QCD) we show that full QCD with a vacuum of vanishing baryonic number does not lead to metastable phases. Rather in QCD with dynamical fermions, the degeneracy of $Z_3$ phases manifests itself in observables without open triality.

hep-lat↗
arXiv1993

Spontaneous Breaking of Chiral Symmetry as a Consequence of Confinement

We show that at the leading order in the large-$N$ expansion a lattice QCD motivated linear rising confinement potential at large distances leads to a non-local four-quark interaction that realizes spontaneous breaking of chiral symmetry (SBCS) in the same way the Nambu-Jona-Lasinio model does. The dynamical quark mass $m$, which represents the solution of the gap-equation, is proportional to the square root of the string tension $σ$ and takes the form at the leading order in the large-$N$ expansion $m=2 \sqrtσ/π$ with $σ=0.27$ GeV$^2$. The Nambu-Jona-Lasinio phenomenological constant $G_1$, which is responsible for SBCS, is expressed in terms of the string tension and the confinement radius.

hep-ph↗
arXiv1993

Charge Screening, Large-N, and the Abelian Projection Model of Confinement

We point out that the abelian projection theory of quark confinement is in conflict with certain large-N predictions. According to both large-N and lattice strong-coupling arguments, the perimeter law behavior of adjoint Wilson loops at large scales is due to charge-screening, and is suppressed relative to the area term by a factor of $1/N^2$. In the abelian projection theory, however, the perimeter law is due to the fact that $N-1$ out of $N^2-1$ adjoint quark degrees of freedom are (abelian) neutral and unconfined; the suppression factor relative to the area law is thus only $1/N$. We study numerically the behavior of Wilson loops and Polyakov lines with insertions of (abelian) charge projection operators, in maximal abelian gauge. It appears from our data that the forces between abelian charged, and abelian neutral adjoint quarks are not significantly different. We also show via the lattice strong-coupling expansion that, at least at strong couplings, QCD flux tubes attract one another, whereas vortices in type II superconductors repel.

hep-lat↗