7,321 research outputs found
Startling Equivalences in the Higgs-Goldstone Sector between Radiative and Lowest-Order Conventional Electroweak Symmetry Breaking
For the Higgs boson mass of GeV expected to arise from radiative
electroweak symmetry breaking, we find the same lowest-order expressions as
would be obtained from conventional electroweak symmetry breaking, given the
same Higgs boson mass, for Higgs-Goldstone sector scattering processes
identified with , , as
well as for Higgs boson decay widths , . The
radiatively broken case, however, leads to an order of magnitude enhancement
over lowest-order conventional symmetry breaking for scattering processes
, , as well as a factor of
enhancement for .Comment: 6 pages, uses ws-ijmpa.cls written in Latex2E. Major revision in text
and conclusions--different enhanced scattering processes found than the
earlier version. To appear in the IJMPA proceedings issue for MRST 2005,
Utica, N
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
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
Pade-Summation Approach to QCD Beta-Function Infrared Properties
We address whether Pad\'e-summations of the QCD -function
for a given number of flavours exhibit an infrared-stable fixed point, or
alternatively, an infrared attractor of a double valued couplant as noted by
Kogan and Shifman for the case of supersymmetric gluodynamics. Below an
approximant-dependent flavour threshold , we find that
Pad\'e-summation -functions incorporating ,
and approximants always exhibit a positive pole prior to the occurrence
of their first positive zero, precluding any identification of this first
positive zero as an infrared-stable fixed point of the - function. This
result is shown to be true regardless of the magnitude of the presently-unknown
five-loop -function contribution. Moreover, the pole in question
suggests the occurrence of dynamics in which both a strong and an
asymptotically-free phase share a common infrared attractor. We briefly discuss
the possible relevance of infrared-attractor dynamics to the success of recent
calculations of the glueball mass spectra in QCD with via
supergravity. As increases above an approximant-dependent flavour
threshold, Pad\'e-summation -functions incorporating , and
approximants exhibit dynamics controlled by an infrared-stable fixed
point over a widening domain of the five-loop -function
parameter . Above this threshold, all approximants
considered exhibit infrared-stable fixed points that decrease in magnitude with
increasing flavour number.Comment: 20 postscript figures now embedded in latex2e. Minor changes to tex
Photoionization and Photoelectric Loading of Barium Ion Traps
Simple and effective techniques for loading barium ions into linear Paul
traps are demonstrated. Two-step photoionization of neutral barium is achieved
using a weak intercombination line (6s2 1S0 6s6p 3P1, 791 nm) followed by
excitation above the ionization threshold using a nitrogen gas laser (337 nm).
Isotopic selectivity is achieved by using a near Doppler-free geometry for
excitation of the triplet 6s6p 3P1 state. Additionally, we report a
particularly simple and efficient trap loading technique that employs an
in-expensive UV epoxy curing lamp to generate photoelectrons.Comment: 5 pages, Accepted to PRA 3/20/2007 -fixed typo -clarified figure 3
caption -added reference [15
Malignancy within a tail gut cyst:a case of retrorectal carcinoid tumour
Purpose. Tailgut cysts with malignant transformation are rare entities. We discuss the diagnostic strategy and treatment of a malignancy within a tailgut cyst. Methods. In this study we report on the case of a 61-year-old man with a malignant neuroendocrine tumour arising within a tailgut cyst and an overview of the literature emphasising the histopathological characteristics and differential diagnosis. Results. Our patient presented with lower back pain, rectal pain, and increased urgency of defecation. MRI scan and CT-guided biopsy on histological analysis revealed a diagnosis of carcinoid tumour of the presacral space. The patient subsequently underwent an abdominoperineal excision of the rectum. Conclusions. This case highlights the importance of tailgut cysts as a differential diagnosis of presacral masses. It is a rare congenital lesion developing from remnants of the embryonic postanal gut and is predominantly benign in nature. Approximately half of cases remain asymptomatic; therefore, diagnosis is often delayed. Magnetic resonance imaging is the investigation of choice and an awareness of the possibility of malignant potential is critical to avoiding missed diagnosis and subsequent morbidity. Complete surgical excision allows accurate diagnosis, confirmation of oncological clearance, and prevention of mortality
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