7,643 research outputs found
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
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
Radiative Electroweak Symmetry-Breaking Revisited
In the absence of a tree-level scalar-field mass, renormalization-group
methods permit the explicit summation of leading-logarithm contributions to all
orders of the perturbative series within the effective potential for
electroweak symmetry. This improvement of the effective
potential function is seen to reduce residual dependence on the renormalization
mass scale. The all-orders summation of leading logarithm terms involving the
dominant three couplings contributing to radiative corrections is suggestive of
a potential characterized by a plausible Higgs boson mass of 216 GeV. However,
the tree potential's local minimum at is restored if QCD is
sufficiently strong.Comment: revtex, 4 pages, 1 eps figure embedded in manuscript. Updated version
contains additional comments and corrects minor error
Buffalo National River Ecosystems - Part II
The priorities were established for the Buffalo National River Ecosystem Studies through meetings and correspondence with Mr. Roland Wauer and other personnel of the Office of Natural Sciences, Southwest Region of the National Park Service. These priorities were set forth in the appendix of contract no. CX 700050443 dated May 21, 1975
The Long and Short of Nuclear Effective Field Theory Expansions
Nonperturbative effective field theory calculations for NN scattering seem to
break down at rather low momenta. By examining several toy models, we clarify
how effective field theory expansions can in general be used to properly
separate long- and short-range effects. We find that one-pion exchange has a
large effect on the scattering phase shift near poles in the amplitude, but
otherwise can be treated perturbatively. Analysis of a toy model that
reproduces 1S0 NN scattering data rather well suggests that failures of
effective field theories for momenta above the pion mass can be due to
short-range physics rather than the treatment of pion exchange. We discuss the
implications this has for extending the applicability of effective field
theories.Comment: 22 pages, 9 figures, references corrected, minor modification
Discovery of extended radio emission in the young cluster Wd1
We present 10 micron, ISO-SWS and Australia Telescope Compact Array
observations of the region in the cluster Wd1 in Ara centred on the B[e] star
Ara C. An ISO-SWS spectrum reveals emission from highly ionised species in the
vicinity of the star, suggesting a secondary source of excitation in the
region. We find strong radio emission at both 3.5cm and 6.3cm, with a total
spatial extent of over 20 arcsec. The emission is found to be concentrated in
two discrete structures, separated by 14''. The westerly source is resolved,
with a spectral index indicative of thermal emission. The easterly source is
clearly extended and nonthermal (synchrotron) in nature. Positionally, the B[e]
star is found to coincide with the more compact radio source, while the
southerly lobe of the extended source is coincident with Ara A, an M2 I star.
Observation of the region at 10micron reveals strong emission with an almost
identical spatial distribution to the radio emission. Ara C is found to have an
extreme radio luminosity in comparison to prior radio observations of hot stars
such as O and B supergiants and Wolf-Rayet stars, given the estimated distance
to the cluster. An origin in a detatched shell of material around the central
star is therefore suggested; however given the spatial extent of the emission,
such a shell must be relatively young (10^3 yrs). The extended non thermal
emission associated with the M star Ara A is unexpected; to the best of our
knowledge this is a unique phenomenon. SAX (2-10keV) observations show no
evidence of X-ray emission, which might be expected if a compact companion were
present.Comment: 5 pages including encapsulated figures, figure 3 separate. Accepted
for MNRAS pink page
The impact of population-based faecal occult blood test screening on colorectal cancer mortality:a matched cohort study
BACKGROUND: Randomised trials show reduced colorectal cancer (CRC) mortality with faecal occult blood testing (FOBT). This outcome is now examined in a routine, population-based, screening programme. METHODS: Three biennial rounds of the UK CRC screening pilot were completed in Scotland (2000–2007) before the roll out of a national programme. All residents (50–69 years) in the three pilot Health Boards were invited for screening. They received a FOBT test by post to complete at home and return for analysis. Positive tests were followed up with colonoscopy. Controls, selected from non-pilot Health Boards, were matched by age, gender, and deprivation and assigned the invitation date of matched invitee. Follow-up was from invitation date to 31 December 2009 or date of death if earlier. RESULTS: There were 379 655 people in each group (median age 55.6 years, 51.6% male). Participation was 60.6%. There were 961 (0.25%) CRC deaths in invitees, 1056 (0.28%) in controls, rate ratio (RR) 0.90 (95% confidence interval (CI) 0.83–0.99) overall and 0.73 (95% CI 0.65–0.82) for participants. Non-participants had increased CRC mortality compared with controls, RR 1.21 (95% CI 1.06–1.38). CONCLUSION: There was a 10% relative reduction in CRC mortality in a routine screening programme, rising to 27% in participants
Can the Renormalization Group Improved Effective Potential be used to estimate the Higgs Mass in the Conformal Limit of the Standard Model?
We consider the effective potential in the standard model with a single
Higgs doublet in the limit that the only mass scale present is
radiatively generated. Using a technique that has been shown to determine
completely in terms of the renormalization group (RG) functions when using the
Coleman-Weinberg (CW) renormalization scheme, we first sum leading-log (LL)
contributions to using the one loop RG functions, associated with five
couplings (the top quark Yukawa coupling , the quartic coupling of the Higgs
field , the SU(3) gauge coupling , and the couplings
and ). We then employ the two loop RG functions with the three couplings
, , to sum the next-to-leading-log (NLL) contributions to and
then the three to five loop RG functions with one coupling to sum all the
contributions to . In order to compute these sums, it is
necessary to convert those RG functions that have been originally computed
explicitly in the minimal subtraction (MS) scheme to their form in the CW
scheme. The Higgs mass can then be determined from the effective potential: the
result is decreases to at
order and at order. No reasonable
estimate of can be made at orders or . This is taken
to be an indication that this mechanism for spontaneous symmetry breaking is in
fact viable, though one in which there is slow convergence towards the actual
value of . The mass is argued to be an upper bound on
.Comment: 24 pages, 5 figures. Updated version contains new discussion,
references, figures, and corrects errors in reference
Diverse Eruptive Activity Revealed by Acoustic and Electromagnetic Observations of the 14 July 2013 Intense Vulcanian Eruption of Tungurahua Volcano, Ecuador
During the powerful July 2013 eruption of Tungurahua volcano, Ecuador, we recorded exceptionally high amplitude, long‐period infrasound (1,600‐Pa peak‐to‐peak amplitude, 5.5‐s period) on sensors within 2km of the vent alongside electromagnetic signals from volcanic lightning serendipitously captured as interference. This explosion was one of Tungurahua\u27s most powerful vulcanian eruptions since recent activity began in 1999, and its acoustic wave is among the most powerful volcanic infrasound ever recorded anywhere. We use these data to quantify erupted volume from the main explosion and to classify postexplosive degassing into distinct emission styles. Additionally, we demonstrate a highly effective method of recording lightning‐related electromagnetic signals alongside infrasound. Detailed chronologies of powerful vulcanian eruptions are rare; this study demonstrates that diverse eruptive processes can occur in such eruptions and that near‐vent infrasound and electromagnetic data can elucidate them
Violation of the Cauchy-Schwarz inequality with matter waves
The Cauchy-Schwarz (CS) inequality -- one of the most widely used and
important inequalities in mathematics -- can be formulated as an upper bound to
the strength of correlations between classically fluctuating quantities.
Quantum mechanical correlations can, however, exceed classical bounds.Here we
realize four-wave mixing of atomic matter waves using colliding Bose-Einstein
condensates, and demonstrate the violation of a multimode CS inequality for
atom number correlations in opposite zones of the collision halo. The
correlated atoms have large spatial separations and therefore open new
opportunities for extending fundamental quantum-nonlocality tests to ensembles
of massive particles.Comment: Final published version (with minor changes). 5 pages, 3 figures,
plus Supplementary Materia
- …