456 research outputs found

### The charm quark's mass in quenched QCD

We present our preliminary result for the charmed quark mass, which follows
from taking the D_s and K meson masses from experiment and r0=0.5 fm (or,
equivalently F_K=160 MeV) to set the scale. For the renormalization group
invariant quark mass we obtain M_c = 1684(64) MeV, which translates to
m_c(m_c)= 1314 (40)(20)(7) MeV for the running mass in the MSbar scheme.
Renormalization is treated non-perturbatively, and the continuum limit has been
taken, so that the only uncontrolled systematic error consists in the use of
the quenched approximation.Comment: Lattice2001(spectrum), 3 page

### Precision muon lifetime and capture experiments at PSI

The muLan experiment at the Paul Scherrer Institute will measure the lifetime
of the positive muon with a precision of 1 ppm, giving a value for the Fermi
coupling constant G_F at the level of 0.5 ppm. Meanwhile, by measuring the
observed lifetime of the negative muon in pure hydrogen, the muCap experiment
will determine the rate of muon capture, giving the proton's pseudoscalar
coupling g_p to 7%. This coupling can be calculated precisely from heavy baryon
chiral perturbation theory and therefore permits a test of QCD's chiral
symmetry.Comment: 4 pages, 2 figures; proceedings of the 6th International Workshop on
Neutrino Factories and Superbeams (NuFACT04), July 26-August 1, 2004, Osaka,
Japan; revised to add one reference (other small edits to conserve length

### Pade-Improved Estimate of Perturbative Contributions to Inclusive Semileptonic $b\to u$ Decays

Pade-approximant methods are used to estimate the three-loop perturbative
contributions to the inclusive semileptonic $b \to u$ decay rate. These
improved estimates of the decay rate reduce the theoretical uncertainty in the
extraction of the CKM matrix element $|V_{ub}|$ from the measured inclusive
semileptonic branching ratio.Comment: 3 pages, latex, write-up of talk presented at DPF 200

### The 4-loop quark mass anomalous dimension and the invariant quark mass

We present the analytical calculation of the four-loop quark mass anomalous
dimension in Quantum Chromodynamics within the minimal subtraction scheme. On
the basis of this result we find that the so-called invariant quark mass is a
very good reference mass for the accurate evolution of the running MS-bar quark
mass in phenomenological applications. We also obtain for the first time a
complete 4-th order perturbative QCD expression for a physical quantity, the
total Higgs boson decay rate into hadrons, and analyze the infrared fixed point
for this case.Comment: 11 pages, Late

### Measurement of the Fermi Constant by FAST

An initial measurement of the lifetime of the positive muon to a precision of
16 parts per million (ppm) has been performed with the FAST detector at the
Paul Scherrer Institute. The result is tau_mu = 2.197083 (32) (15) microsec,
where the first error is statistical and the second is systematic. The muon
lifetime determines the Fermi constant, G_F = 1.166353 (9) x 10^-5 GeV^-2 (8
ppm).Comment: 15 pages, 6 figure

### Three-loop renormalization of the N=1, N=2, N=4 supersymmetric Yang-Mills theories

We calculate the renormalization constants of the N=1, N=2, N=4
supersymmetric Yang-Mills theories in an arbitrary covariant gauge in the
dimensional reduction scheme up to three loops. We have found, that the
beta-functions for N=1 and N=4 SYM theories are the same from the different
triple vertices. This means that the dimensional reduction scheme works
correctly in these models up to third order of perturbative theory.Comment: 6 page

### Renormalization-Scheme-Independent Perturbation Theory by Resumming Logarithms

Results of perturbation theory in quantum field theory generally depend on
the renormalization scheme that is in use. In particular, they depend on the
scale. We try to make perturbation theory scheme invariant by re-expanding with
respect to a scheme invariant quantity. Furthermore, we investigate whether the
potentially large logarithms in such an expansion cause inaccuracy and how this
can be improved.Comment: 15 pages, 2 figures. First replaced version: added one reference.
Second replaced version: added two references, mention effective-charge
method, added remarks about further research possibilities, changed size of
graphs a littl

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