arXiv subjects

Ulrich Ellwanger

Publications and source records attributed to Ulrich Ellwanger.

61 records · Page 4Linked to original sources

arXiv1997

The Heavy Quark Potential from Wilson's Exact Renormalization Group

We perform a calculation of the full momentum dependence of the gluon and ghost propagators in pure SU(3) Yang-Mills theory by integrating Wilson's exact renormalization group equations with respect to an infrared cutoff k. The heavy quark potential in the quenched approximation can be expressed in terms of these propagators. Our results strongly indicate a 1/p^4 behaviour of the heavy quark potential for $p^2 \to 0$. We show in general, that effective actions which satisfy Schwinger-Dyson equations, correspond to (quasi-) fixed points of Wilson's exact renormalization group equations.

hep-ph↗

arXiv1997

The Running Gauge Coupling in the Exact Renormalization Group Approach

We discuss the perturbative running Yang-Mills coupling constant in the Wilsonian exact renormalization group approach, and compare it to the running coupling in the more conventional MS-bar scheme. The exact renormalization group approach corresponds to a particular renormalization scheme, and we relate explicitly the corresponding Lambda-parameters. The unambiguous definition of an exact renormalization group scheme requires, however, the use of a one-loop improved high energy effective action.

hep-ph↗

arXiv1994

Flow Equations and BRS Invariance for Yang-Mills Theories

Flow equations describe the evolution of the effective action $Γ_k$ in the process of varying an infrared cutoff $k$. The presence of the infrared cutoff explicitly breaks gauge and hence BRS invariance. We derive modified Slavnov-Taylor identities, which are valid for nonvanishing $k$. They guarantee the BRS invariance of $Γ_k$ for $k\to0$, and hence allow the study of non-abelian gauge theories by integrating the flow equations. Within a perturbative expansion of $Γ_k$, we derive an equation for a $k$ dependent mass term for the gauge fields implied by the modified Slavnov-Taylor identities.

hep-th↗

arXiv1993

Flow Equations for N Point Functions and Bound States

We discuss the exact renormalization group or flow equation for the effective action and its decomposition into one particle irreducible N point functions. With the help of a truncated flow equation for the four point function we study the bound state problem for scalar fields. A combination of analytic and numerical methods is proposed, which is applied to the Wick-Cutkosky model and a QCD-motivated interaction. We present results for the bound state masses and the Bethe-Salpeter wave function. (Figs. 1-4 attached as separate uuencoded post-script files.)

hep-ph↗

arXiv1993

Particle Spectrum in Supersymmetric Models with a Gauge Singlet

We scan the complete parameter space of the supersymmetric standard model extended by a gauge singlet, which is compatible with the following constraints: universal soft supersymmetry breaking terms at the GUT scale, finite running Yukawa couplings up to the GUT scale and present experimental bounds on all sparticles, Higgs scalar and top quark. The full radiative corrections to the Higgs potential due to the top/stop sector are included. We find a lower limit on the gluino mass of 160 GeV, upper limits on the lightest neutral scalar Higgs mass dependent on $m_{top}$ and the size of the soft supersymmetry breaking terms, and the possibility of a Higgs scalar as light as 10 GeV, but with reduced couplings to the Z boson.

hep-ph↗

arXiv1993

Radiative Corrections to the Neutral Higgs Spectrum in Supersymmetry with a Gauge Singlet

The radiative corrections to the $3\times3$scalar and the $2\times2$ pseudoscalar neutral Higgs boson massmatrices are calculated in the supersymmetric extension of the standard model including a gauge singlet superfield in the effective potential approach. The full $t$ and $b$ quark/squark contributions including the nonlogarithmic terms are taken into account, which are seen to affect the result significantly. An analytic formula for the upper bound on the mass of the lightest neutral Higgs scalar including these corrections is given. (Figure available upon request)

hep-ph↗

arXiv1992

Nonperturbative Conditions for Local Weyl Invariance on a Curved World Sheet

We investigate Weyl anomalies on a curved world sheet to second order in a weak field expansion. Using a local version of the exact renormalization group equations, we obtain nonperturbative results for the tachyon/graviton/dilaton system. We discuss the elimination of redundant operators, which play a crucial role for the emergence of target space covariance. Performing the operator product expansion on a curved world sheet allows us to obtain the nonperturbative contributions to the dilaton $β$ function. We find the $β$ functions, after suitable field redefinitions, to be related to a target space effective action through a $κ$ function involving derivatives. Also we can establish a nonperturbative Curci-Paffuti relation including the tachyon $β$ function.

hep-th↗