4,064 research outputs found
Damping Rate of a Yukawa Fermion at Finite Temperature
The damping of a massless fermion coupled to a massless scalar particle at
finite temperature is considered using the Braaten-Pisarski resummation
technique. First the hard thermal loop diagrams of this theory are extracted
and effective Green's functions are constructed. Using these effective Green's
functions the damping rate of a soft Yukawa fermion is calculated. This rate
provides the most simple example for the damping of a soft particle. To leading
order it is proportional to , whereas the one of a hard fermion is of
higher order.Comment: 5 pages, REVTEX, postscript figures appended, UGI-94-0
Radio-chemotherapy as a preoperative treatment for advanced rectal cancer. Evaluation of down-staging and morbidity
Background: The standard therapy for patients with clinically resectable rectal cancer is generally considered to be surgery, If the patient is diagnosed with advanced disease, postoperative radiochemotherapy (RCT) is usually recommended. In our study we aimed to investigate and analyze the effectiveness and toxicity of preoperative pelvic radiotherapy in combination with 5-fluorouracil (5-FU) in locally advanced rectal cancer. Patients and Methods: From June 1999 to September 2001 we evaluated 50 consecutive patients {[}37 male and 13 female; average age 65.1 (range 46-79.5) years] with locally advanced rectal carcinoma. 32 patients were staged as uT3, 14 as uT4, and 4 as uT2. Regarding N-staging, 22 patients were diagnosed as ONO. 2 patients had distant metastases, with liver metastases in both instances. Conformal irradiation was performed with a box technique 4-field technique) with a dose of 45 Gy (5 x 1.8 Gy per week for a total of 25 sessions). From days 1-5 and 29-33, all patients received 5-FU (500 mg/m(2) per day, as a continuous i.v. injection). Results: Remission was observed in 28 patients (56%), with down-staging of at least one T-stage. A better success rate was achieved for patients with deep-seated tumors (64% of the patients in this group). Complete remission was observed in 4 patients (8.0%) and progression in 3 (6.0%). 15 patients had no detectable change in tumor staging (30.0%). A surgical R0 resection could be achieved in 43 patients, an R1 resection (minimal margins in 7. Side effects and toxicity (common toxicity criteria) of RCT included grade I-II dysuria in 5 patients (10%), grade I-II diarrhea in 20 patients (40%), and severe diarrhea in 2 patients (4.0%). Grade I-II skin reaction was noticed in 22 patients (44.0%), severe skin reaction only in 1 patient. Regarding acute postoperative morbidity, abscess and fistula formation was noted in 8 patients (16.0%), with anastomosis leakage in 7 (14%). Conclusion: Preoperative radiotherapy appears to be a feasible therapeutic approach with moderate toxicity and the potential to induce down-staging. The data presented in this study confirm the preliminary reports on this neoadjuvant treatment
Damping Rate of a Hard Photon in a Relativistic Plasma
The damping rate of a hard photon in a hot relativistic QED and QCD plasma is
calculated using the resummation technique by Braaten and Pisarski.Comment: 4 pages, REVTeX, 2 figures (not included), UGI-MT-94-0
Collisional Energy Loss of Fast Charged Particles in Relativistic Plasmas
Following an argument by Kirzhnits we rederive an exact expression for the
energy loss of a fast charged particle in a relativistic plasma using the
quantum field theoretical language. We compare this result to perturbative
calculations of the collisional energy loss of an energetic electron or muon in
an electron-positron plasma and of an energetic parton in the quark-gluon
plasma.Comment: 9 pages, LATEX, 2 PostScript figure
Study of ambiguities in scattering amplitudes
Amplitudes for the reaction are reconstructed from
data on the differential cross section , the recoil
polarization , and on the spin rotation parameter . At low energies,
no data on exist, resulting in ambiguities. An approximation using
and waves leads only to a fair description of the data on
and ; in this case, there are two sets of amplitudes. Including waves,
the data on and are well reproduced by the fit but now,
there are several distinct solutions which describe the data with identical
precision. In the range where the spin rotation parameter was measured,
a full and unambiguous reconstruction of the partial wave amplitudes is
possible. The energy-independent amplitudes are compared to the energy
dependent amplitudes which resulted from a coupled channel fit (BnGa2011-02) to
a large data set including both pion and photo-induced reactions. Significant
deviations are observed. Consistency between energy dependent and energy
independent solutions by choosing the energy independent solution which is
closest to the energy dependent solution. In a second step, the {\it known}
energy dependent solution for low (or high) partial waves is imposed and only
the high (or low) partial waves are fitted leading to smaller uncertainties
The Quark-Gluon-Plasma Liquid
The quark-gluon plasma close to the critical temperature is a strongly
interacting system. Using strongly coupled, classical, non-relativistic plasmas
as an analogy, we argue that the quark-gluon plasma is in the liquid phase.
This allows to understand experimental observations in ultrarelativistic
heavy-ion collisions and to interpret lattice QCD results. It also supports the
indications of the presence of a strongly coupled QGP in ultrarelativistic
heavy-ion collisions.Comment: 8 pages, 2 figures, final version, to bepublished in J. Phys.
Decay of a Yukawa fermion at finite temperature and applications to leptogenesis
We calculate the decay rate of a Yukawa fermion in a thermal bath using
finite temperature cutting rules and effective Green's functions according to
the hard thermal loop resummation technique. We apply this result to the decay
of a heavy Majorana neutrino in leptogenesis. Compared to the usual approach
where thermal masses are inserted into the kinematics of final states, we find
that deviations arise through two different leptonic dispersion relations. The
decay rate differs from the usual approach by more than one order of magnitude
in the temperature range which is interesting for the weak washout regime. We
discuss how to arrive at consistent finite temperature treatments of
leptogenesis.Comment: 16 pages, 5 figure
Field Theoretic Description of Ultrarelativistic Electron-Positron Plasmas
Ultrarelativistic electron-positron plasmas can be produced in high-intensity
laser fields and play a role in various astrophysical situations. Their
properties can be calculated using QED at finite temperature. Here we will use
perturbative QED at finite temperature for calculating various important
properties, such as the equation of state, dispersion relations of collective
plasma modes of photons and electrons, Debye screening, damping rates, mean
free paths, collision times, transport coefficients, and particle production
rates, of ultrarelativistic electron-positron plasmas. In particular, we will
focus on electron-positron plasmas produced with ultra-strong lasers.Comment: 13 pages, 7 figures, 1 table, published versio
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