6,930 research outputs found
Consequences of Leading-Logarithm Summation for the Radiative Breakdown of Standard-Model Electroweak Symmetry
In the empirically sensible limit in which QCD, t-quark Yukawa, and
scalar-field-interaction coupling constants dominate all other Standard-Model
coupling constants, we sum all leading-logarithm terms within the perturbative
expansion for the effective potential that contribute to the extraction of the
Higgs boson mass via radiative electroweak symmetry breaking. A Higgs boson
mass of 216 GeV emerges from such terms, as well as a scalar-field-interaction
coupling constant substantially larger than that anticipated from conventional
spontaneous symmetry breaking. The sum of the effective potential's leading
logarithms is shown to exhibit a local minimum in the limit if the
QCD coupling constant is sufficiently strong, suggesting (in a multiphase
scenario) that electroweak physics may provide the mechanism for choosing the
asymptotically-free phase of QCD.Comment: latex using aip proceedings class. 8 page write-out of presentation
at MRST 2003 Conference (Syracuse
Improvement of Renormalization-Scale Uncertainties Within Empirical Determinations of the b-Quark Mass
Accurate determinations of the MS-bar b-quark mass from
experimental data currently contain three
comparable sources of uncertainty; the experimental uncertainty from moments of
this cross-section, the uncertainty associated with , and the
theoretical uncertainty associated with the renormalization scale. Through
resummation of all logarithmic terms explicitly determined in the perturbative
series by the renormalization-group (RG) equation, it is shown that the
renormalization-scale dependence is virtually eliminated as a source of
theoretical uncertainty in . This resummation also reduces the
estimated effect of higher-loop perturbative contributions, further reducing
the theoretical uncertainties in . Furthermore, such resummation
techniques improve the agreement between the values of the MS-bar b-quark mass
extracted from the various moments of [], obviating the need to
choose an optimummoment for determining . Resummation techniques are
also shown to reduce renormalization-scale dependence in the relation between
b-quark MS-bar and pole mass and in the relation between the pole and
mass.Comment: 19 pages, latex2e, 6 eps figures contained in latex file. Errors
corrected in equations (20)--(22
Pade-Improved Estimate of Perturbative Contributions to Inclusive Semileptonic Decays
Pade-approximant methods are used to estimate the three-loop perturbative
contributions to the inclusive semileptonic decay rate. These
improved estimates of the decay rate reduce the theoretical uncertainty in the
extraction of the CKM matrix element from the measured inclusive
semileptonic branching ratio.Comment: 3 pages, latex, write-up of talk presented at DPF 200
Higher Order Stability of a Radiatively Induced 220 GeV Higgs Mass
The effective potential for radiatively broken electroweak symmetry in the
single Higgs doublet Standard Model is explored to four sequentially subleading
logarithm-summation levels (5-loops) in the dominant Higgs self-interaction
couplant . We augment these results with all contributing leading
logarithms in the remaining large but sub-dominant Standard Model couplants
(t-quark, QCD and gauge couplants) as well as next to
leading logarithm contributions from the largest of these, the t-quark and QCD
couplants. Order-by-order stability is demonstrated for earlier leading
logarithm predictions of an order 220 GeV Higgs boson mass in conjunction with
fivefold enhancement of the value for over that anticipated from
conventional spontaneous symmetry breaking.Comment: revtex, 6 pages. Analysis and text is expanded in revised versio
On the Standard Approach to Renormalization Group Improvement
Two approaches to renormalization-group improvement are examined: the
substitution of the solutions of running couplings, masses and fields into
perturbatively computed quantities is compared with the systematic sum of all
the leading log (LL), next-to-leading log (NLL) etc. contributions to
radiatively corrected processes, with n-loop expressions for the running
quantities being responsible for summing N^{n}LL contributions. A detailed
comparison of these procedures is made in the context of the effective
potential V in the 4-dimensional O(4) massless model,
showing the distinction between these procedures at two-loop order when
considering the NLL contributions to the effective potential V.Comment: 6 page
Impeded Growth of Magnetic Flux Bubbles in the Intermediate State Pattern of Type I Superconductors
Normal state bubble patterns in Type I superconducting Indium and Lead slabs
are studied by the high resolution magneto-optical imaging technique. The size
of bubbles is found to be almost independent of the long-range interaction
between the normal state domains. Under bubble diameter and slab thickness
proper scaling, the results gather onto a single master curve. On this basis,
in the framework of the "current-loop" model [R.E. Goldstein, D.P. Jackson and
A.T. Dorsey, Phys. Rev. Lett. 76, 3818 (1996)], we calculate the equilibrium
diameter of an isolated bubble resulting from the competition between the
Biot-and-Savart interaction of the Meissner current encircling the bubble and
the superconductor-normal interface energy. A good quantitative agreement with
the master curve is found over two decades of the magnetic Bond number. The
isolation of each bubble in the superconducting matrix and the existence of a
positive interface energy are shown to preclude any continuous size variation
of the bubbles after their formation, contrary to the prediction of mean-field
models.Comment: \'{e}quipe Nanostructures Quantique
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