430 research outputs found
Global Wilson-Fisher fixed points
The Wilson-Fisher fixed point with universality in three dimensions is
studied using the renormalisation group. It is shown how a combination of
analytical and numerical techniques determine global fixed point solutions to
leading order in the derivative expansion for real or purely imaginary fields
with moderate numerical effort. Universal and non-universal quantitites such as
scaling exponents and mass ratios are computed, for all , together with
local fixed point coordinates, radii of convergence, and parameters which
control the asymptotic behaviour of the effective action. We also explain when
and why finite- results do not converge pointwise towards the exact
infinite- limit. In the regime of purely imaginary fields, a new link
between singularities of fixed point effective actions and singularities of
their counterparts by Polchinski are established. Implications for other
theories are indicated.Comment: 28 pages, 10 figures, v2: explanations and refs added, to appear
(NPB
An exploratory study of heavy domain wall fermions on the lattice
We report on an exploratory study of domain wall fermions (DWF) as a lattice
regularisation for heavy quarks. Within the framework of quenched QCD with the
tree-level improved Symanzik gauge action we identify the DWF parameters which
minimise discretisation effects. We find the corresponding effective 4
overlap operator to be exponentially local, independent of the quark mass. We
determine a maximum bare heavy quark mass of , below which the
approximate chiral symmetry and O(a)-improvement of DWF are sustained. This
threshold appears to be largely independent of the lattice spacing. Based on
these findings, we carried out a detailed scaling study for the heavy-strange
meson dispersion relation and decay constant on four ensembles with lattice
spacings in the range . We observe very mild
scaling towards the continuum limit. Our findings establish a sound basis for
heavy DWF in dynamical simulations of lattice QCD with relevance to Standard
Model phenomenology.Comment: 23 pages, 8 figure
The decay constants and in the continuum limit of domain wall lattice QCD
We present results for the decay constants of the and mesons
computed in lattice QCD with dynamical flavours. The simulations are
based on RBC/UKQCD's domain wall ensembles with both physical and unphysical
light-quark masses and lattice spacings in the range 0.11--0.07fm. We
employ the domain wall discretisation for all valence quarks.
The results in the continuum limit are
and
and
.
Using these results in a Standard Model analysis we compute the predictions
and
for the
CKM matrix elements
Commuting quantum transfer matrix approach to intrinsic Fermion system: Correlation length of a spinless Fermion model
The quantum transfer matrix (QTM) approach to integrable lattice Fermion
systems is presented. As a simple case we treat the spinless Fermion model with
repulsive interaction in critical regime. We derive a set of non-linear
integral equations which characterize the free energy and the correlation
length of for arbitrary particle density at any finite
temperatures. The correlation length is determined by solving the integral
equations numerically. Especially in low temperature limit this result agrees
with the prediction from conformal field theory (CFT) with high accuracy.Comment: 17 page
Relativistic diffusive motion in random electromagnetic fields
We show that the relativistic dynamics in a Gaussian random electromagnetic
field can be approximated by the relativistic diffusion of Schay and Dudley.
Lorentz invariant dynamics in the proper time leads to the diffusion in the
proper time. The dynamics in the laboratory time gives the diffusive transport
equation corresponding to the Juettner equilibrium at the inverse temperature
\beta^{-1}=mc^{2}. The diffusion constant is expressed by the field strength
correlation function (Kubo's formula).Comment: the version published in JP
Exact thermodynamics of an Extended Hubbard Model of single and paired carriers in competition
By exploiting the technique of Sutherland's species, introduced in
\cite{DOMO-RC}, we derive the exact spectrum and partition function of a 1D
extended Hubbard model. The model describes a competition between dynamics of
single carriers and short-radius pairs, as a function of on-site Coulomb
repulsion () and filling (). We provide the temperature dependence of
chemical potential, compressibility, local magnetic moment, and specific heat.
In particular the latter turns out to exhibit two peaks, both related to
`charge' degrees of freedom. Their origin and behavior are analyzed in terms of
kinetic and potential energy, both across the metal-insulator transition point
and in the strong coupling regime.Comment: 14 pages, 15 eps figure
Thoracic wall reconstruction using both portions of the latissimus dorsi previously divided in the course of posterolateral thoracotomy
Objective: Besides other factors, the choice of reconstructive method for full thickness thoracic wall defects depends on the morbidity of preceding surgical procedures. The pedicled latissimus dorsi flap is a reliable and safe option for reconstruction of the thorax. A posterolateral thoracotomy, however, results in division of the muscle. Both parts of the muscle can be employed to close full thickness defects of the chest wall. The proximal part can be pedicled on the thoracodorsal vessels or the serratus branch; the distal part can be pedicled on paravertebral or intercostal perforators. This retrospective study was undertaken to evaluate the reconstructive potential of both parts of the latissimus dorsi in thoracic wall reconstruction after posterolateral thoracotomy. Methods: Between 1987 and 1999, 36 consecutive patients underwent reconstruction of full-thickness thoracic wall defects with latissimus dorsi-flaps after posterolateral thoracotomies. The defects resulted from infection and open window thoracostomy (n=31), trauma (n=3) and resection of tumours (n=2). The patients' average age was 57 years (range 22-76 years). Twenty-five patients were male, 11 were female. In 31 cases the split latissimus dorsi alone was employed; in five cases additional flaps had to be used due to the size of the defects, additional intrathoracic problems or neighbouring defects. Results: In 34 cases defect closure could be achieved without major complications. Empyema recurred in the pleural cavity in one case and one patient died of septicaemia. The 15 patients who had required a respirator in the preoperative phase could be extubated 4.8 days (average) after thoracic wall reconstruction. Postoperative hospital stay averaged 16 days. Conclusions: Different methods are available for reconstruction of full thickness defects of the thoracic wall. After posterolateral thoracotomy in the surgical treatment of empyema, oncologic surgery and traumatology, the latissimus dorsi muscle still retains some reconstructive potential. Advantages are low additional donor site morbidity and anatomical reliability. As it is located near the site of the defect, there is no need for additional surgical sites or intraoperative repositioning. In our service, the split latissimus dorsi muscle flap has proven to be a valuable and reliable option in thoracic wall reconstructio
Collision Thermalization of Nucleons in Relativistic Heavy-Ion Collisions
We consider a possible mechanism of thermalization of nucleons in
relativistic heavy-ion collisions. Our model belongs, to a certain degree, to
the transport ones; we investigate the evolution of the system created in
nucleus-nucleus collision, but we parametrize this development by the number of
collisions of every particle during evolution rather than by the time variable.
We based on the assumption that the nucleon momentum transfer after several
nucleon-nucleon (-hadron) elastic and inelastic collisions becomes a random
quantity driven by a proper distribution. This randomization results in a
smearing of the nucleon momenta about their initial values and, as a
consequence, in their partial isotropization and thermalization. The trial
evaluation is made in the framework of a toy model. We show that the proposed
scheme can be used for extraction of the physical information from experimental
data on nucleon rapidity distribution.Comment: 13 pages, 8 figure
A simplistic pedagogical formulation of a thermal speed distribution using a relativistic framework
A novel pedagogical technique is presented that can be used in the
undergraduate (UG) class to formulate a relativistically extended Kinetic
Theory of Gases and thermal speed distribution, while assuming the basic
thermal symmetry arguments of the famous Maxwell-Boltzmann distribution as
presented at the UG level. The adopted framework can be used by students to
understand the physics in a thermally governed system at high temperature and
speeds, without having to indulge in high level tensor based mathematics, as
has been done by the previous works in the subject. Our approach, a logical
extension of that proposed by Maxwell, will first recapitulate what is taught
and known in the UG class and then present a methodology inspired from the
Maxwell-Boltzmann framework that will help students to understand and derive
the physics of relativistic thermal systems. The methodology uses simple tools
well known to undergraduates and involves a component of computational
techniques that can be used to involve students in this exercise. We have tried
to place the current work in a larger perspective in regard to the earlier
works done and emphasize on it's simplicity and accessibility to students.
Towards the end, interesting implications of the relativistically extended
distribution are presented and compared with the Maxwell-Boltzmann results at
various temperatures.Comment: 13 pages, 5 figures, Publication accepted in Pramana - Journal of
Physics (Indian Academy of Sciences). Revised version has an additional
section, discussing previous work on relativistic Kinetic Theory in section
2.1 and comparison with these in section 6. Arguments for formulating a
relativistic thermal speed distributions have been enriched and made more
clear and categorical in section
Lattice path integral approach to the one-dimensional Kondo model
An integrable Anderson-like impurity model in a correlated host is derived
from a gl(21)-symmetric transfer matrix by means of the
Quantum-Inverse-Scattering-Method (QISM). Using the Quantum Transfer Matrix
technique, free energy contributions of both the bulk and the impurity are
calculated exactly. As a special case, the limit of a localized moment in a
free bulk (Kondo limit) is performed in the Hamiltonian and in the free energy.
In this case, high- and low-temperature scales are calculated with high
accuracy.Comment: 26 pages, 9 figure
- …