1,426 research outputs found
Next-to-leading order multi-leg processes for the Large Hadron Collider
In this talk we discuss recent progress concerning precise predictions for
the LHC. We give a status report of three applications of our method to deal
with multi-leg one-loop amplitudes: The interference term of Higgs production
by gluon- and weak boson fusion to order O(alpha^2 alpha_s^3) and the
next-to-leading order corrections to the two processes pp -> ZZ jet and u ubar
-> d dbar s sbar. The latter is a subprocess of the four jet cross section at
the LHC.Comment: 6 pages, 5 figures. Talk given at the 8th international Symposium on
Radiative Corrections (RADCOR), October 1-5 2007, Florence, Ital
The electronic structure of the heavy fermion metal
The electronic structure of the first reported heavy fermion compound without
f-electrons LiV_2O_4 was studied by an ab-initio calculation method. In the
result of the trigonal splitting and d-d Coulomb interaction one electron of
the configuration of V ion is localized and the rest partially fills
a relatively broad conduction band. The effective Anderson impurity model was
solved by Non-Crossing-Approximation method, leading to an estimation for the
single-site Kondo energy scale T_K. Then, we show how the so-called exhaustion
phenomenon of Nozi\`eres for the Kondo lattice leads to a remarkable decrease
of the heavy-fermion (or coherence) energy scale (D
is the typical bandwidth), comparable to the experimental result.Comment: 4 pages, RevTeX; 3 figures in format .eps. submitted to PR
Survey of the needs of patients with spinal cord injury: impact and priority for improvement in hand function in tetraplegics\ud
Objective: To investigate the impact of upper extremity deficit in subjects with tetraplegia.\ud
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Setting: The United Kingdom and The Netherlands.\ud
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Study design: Survey among the members of the Dutch and UK Spinal Cord Injury (SCI) Associations.\ud
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Main outcome parameter: Indication of expected improvement in quality of life (QOL) on a 5-point scale in relation to improvement in hand function and seven other SCI-related impairments.\ud
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Results: In all, 565 subjects with tetraplegia returned the questionnaire (overall response of 42%). Results in the Dutch and the UK group were comparable. A total of 77% of the tetraplegics expected an important or very important improvement in QOL if their hand function improved. This is comparable to their expectations with regard to improvement in bladder and bowel function. All other items were scored lower.\ud
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Conclusion: This is the first study in which the impact of upper extremity impairment has been assessed in a large sample of tetraplegic subjects and compared to other SCI-related impairments that have a major impact on the life of subjects with SCI. The present study indicates a high impact as well as a high priority for improvement in hand function in tetraplegics.\ud
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Three-loop matching coefficients for hot QCD: Reduction and gauge independence
We perform an integral reduction for the 3-loop effective gauge coupling and
screening mass of QCD at high temperatures, defined as matching coefficients
appearing in the dimensionally reduced effective field theory (EQCD).
Expressing both parameters in terms of a set master (sum-) integrals, we show
explicit gauge parameter independence. The lack of suitable methods for solving
the comparatively large number of master integrals forbids the complete
evaluation at the moment. Taking one generic class of masters as an example, we
highlight the calculational techniques involved. The full result would allow to
improve on one of the classic probes for the convergence of the weak-coupling
expansion at high temperatures, namely the comparison of full and effective
theory determinations of the spatial string tension. Furthermore, the full
result would also allow to determine one new contribution of order O(g**7) to
the pressure of hot QCD.Comment: 19 pages, 2 figures. v2: new Section 6 discussing applications, to
match journal versio
Long-Term Mortality in Patients with Tuberculous Meningitis: A Danish Nationwide Cohort Study
Background: With high short-term mortality and substantial excess morbidity among survivors, tuberculous meningitis (TBM) is the most severe manifestation of extra-pulmonary tuberculosis (TB). The objective of this study was to assess the long-term mortality and causes of death in a TBM patient population compared to the background population. Methods: A nationwide cohort study was conducted enrolling patients notified with TBM in Denmark from 1972–2008 and alive one year after TBM diagnosis. Data was extracted from national registries. From the background population we identified a control cohort of individuals matched on gender and date of birth. Kaplan-Meier survival curves and Cox regression analysis were used to estimate mortality rate ratios (MRR) and analyse causes of death. Findings: A total of 55 TBM patients and 550 individuals from the background population were included in the study. Eighteen patients (32.7%) and 107 population controls (19.5%) died during the observation period. The overall MRR was 1.79 (95%CI: 1.09–2.95) for TBM patients compared to the population control cohort. TBM patients in the age group 31–60 years at time of diagnosis had the highest relative risk of death (MRR 2.68; 95%CI 1.34–5.34). The TBM patients had a higher risk of death due to infectious disease, but not from other causes of death. Conclusion: Adult TBM patients have an almost two-fold increased long-term mortality and the excess mortality stems fro
Stresses in silos: Comparison between theoretical models and new experiments
We present precise and reproducible mean pressure measurements at the bottom
of a cylindrical granular column. If a constant overload is added, the pressure
is linear in overload and nonmonotonic in the column height. The results are
{\em quantitatively} consistent with a local, linear relation between stress
components, as was recently proposed by some of us. They contradict the
simplest classical (Janssen) approximation, and may pose a rather severe test
of competing models.Comment: 4 pages, 2 figures, final version to appear in Phys. Rev. Let
Golem95C: A library for one-loop integrals with complex masses
We present a program for the numerical evaluation of scalar integrals and
tensor form factors entering the calculation of one-loop amplitudes which
supports the use of complex masses in the loop integrals. The program is built
on an earlier version of the golem95 library, which performs the reduction to a
certain set of basis integrals using a formalism where inverse Gram
determinants can be avoided. It can be used to calculate one-loop amplitudes
with arbitrary masses in an algebraic approach as well as in the context of a
unitarity-inspired numerical reconstruction of the integrand.Comment: 22 pages, 3 figure
Effect of nearest neighbor repulsion on the low frequency phase diagram of a quarter-filled Hubbard-Holstein chain
We have studied the influence of nearest-neighbor (NN) repulsion on the low
frequency phase diagram of a quarter-filled Hubbard-Holstein chain. The NN
repulsion term induces the apparition of two new long range ordered phases (one
CDW for positive and one CDW for
negative ) that did not exist in the V=0 phase diagram. These results
are put into perspective with the newly observed charge ordered phases in
organic conductors and an interpretation of their origin in terms of
electron-molecular vibration coupling is suggested.Comment: 10 pages, 10 figure
Suppression of Mott–Hubbard states and metal–insulator transitions in the two-band Hubbard model
I investigate band and Mott insulating states in a two-band Hubbard model, with the aim of understanding the differences between the idealized one-orbital model and the more realistic multi-band case. Using a projection ansatz I show that additional orbitals suppress the metal–insulator transition, leading to a critical coupling of approximately eight times the bare bandwidth. I also demonstrate the effects of orbital ordering, which hinder Mott–Hubbard states and open a bandgap. Since multi-band correlations are common in real materials, this work suggests that very strongly correlated band insulators may be more common than Mott–Hubbard insulators
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