9 research outputs found
Laser processing effect on magnetic properties of amorphous wires
A study was conducted to observe the laser processing effects on the magnetic properties of amorphous wires. Weekly interacting heterogeneous structures with different magnetic properties were formed by the local annealing by argon laser. Favourable changes were observed due to the creation of local stresses and structural interfaces
Chiral condensates from tau decay: a critical reappraisal
The saturation of QCD chiral sum rules is reanalyzed in view of the new and
complete analysis of the ALEPH experimental data on the difference between
vector and axial-vector correlators (V-A). Ordinary finite energy sum rules
(FESR) exhibit poor saturation up to energies below the tau-lepton mass. A
remarkable improvement is achieved by introducing pinched, as well as
minimizing polynomial integral kernels. Both methods are used to determine the
dimension d=6 and d=8 vacuum condensates in the Operator Product Expansion,
with the results: {O}_{6}=-(0.00226 \pm 0.00055) GeV^6, and O_8=-(0.0053 \pm
0.0033) GeV^8 from pinched FESR, and compatible values from the minimizing
polynomial FESR. Some higher dimensional condensates are also determined,
although we argue against extending the analysis beyond dimension d = 8. The
value of the finite remainder of the (V-A) correlator at zero momentum is also
redetermined: \Pi (0)= -4 \bar{L}_{10}=0.02579 \pm 0.00023. The stability and
precision of the predictions are significantly improved compared to earlier
calculations using the old ALEPH data. Finally, the role and limits of
applicability of the Operator Product Expansion in this channel are clarified.Comment: Replaced versio
Supersymmetric Regularization, Two-Loop QCD Amplitudes and Coupling Shifts
We present a definition of the four-dimensional helicity (FDH) regularization
scheme valid for two or more loops. This scheme was previously defined and
utilized at one loop. It amounts to a variation on the standard 't
Hooft-Veltman scheme and is designed to be compatible with the use of helicity
states for "observed" particles. It is similar to dimensional reduction in that
it maintains an equal number of bosonic and fermionic states, as required for
preserving supersymmetry. Supersymmetry Ward identities relate different
helicity amplitudes in supersymmetric theories. As a check that the FDH scheme
preserves supersymmetry, at least through two loops, we explicitly verify a
number of these identities for gluon-gluon scattering (gg to gg) in
supersymmetric QCD. These results also cross-check recent non-trivial two-loop
calculations in ordinary QCD. Finally, we compute the two-loop shift between
the FDH coupling and the standard MS-bar coupling, alpha_s. The FDH shift is
identical to the one for dimensional reduction. The two-loop coupling shifts
are then used to obtain the three-loop QCD beta function in the FDH and
dimensional reduction schemes.Comment: 44 pages, minor corrections and clarifications include
Calculations of binding energies and masses of heavy quarkonia using renormalon cancellation
We use various methods of Borel integration to calculate the binding ground
energies and masses of b-bbar and t-tbar quarkonia. The methods take into
account the leading infrared renormalon structure of the hard+soft part of the
binding energies E(s), and of the corresponding quark pole masses m_q, where
the contributions of these singularities in M(s) = 2 m_q + E(s) cancel.
Beforehand, we carry out the separation of the binding energy into its
hard+soft and ultrasoft parts. The resummation formalisms are applied to
expansions of m_q and E(s) in terms of quantities which do not involve
renormalon ambiguity, such as MSbar quark mass, and alpha_s. The
renormalization scales are different in calculations of m_q, E(s) and E(us).
The MSbar mass of b quark is extracted, and the binding energies of t-tbar and
the peak (resonance) energies for (t+tbar) production are obtained.Comment: 23 pages, 8 double figures, revtex4; the version to appear in
Phys.Rev.D; extended discussion between Eqs.(25) and (26); the paragraph
between Eqs.(32) and (33) is new and explains the numerical dependence of the
residue parameter on the factorization scale; several new references were
added; acknowledgments were modified; the numerical results are unchange
Heavy baryon properties with NLO accuracy in perturbative QCD
We present an analysis of the static properties of heavy baryons at
next-to-leading order in the perurbative expansion of QCD. We obtain analytical
next-to-leading order three-loop results for the two-point correlators of
baryonic currents with one finite mass quark field for a variety of quantum
numbers of the baryonic currents. We consider both the massless limit and the
HQET limit of the correlator as special cases of the general finite mass
formula and find agreement with previous results. We present closed form
expressions for the moments of the spectral density. We determine the residues
of physical baryon states using sum rule techniques.Comment: 43 pages in LaTeX, including 3 figure