261 research outputs found
Radiative and non radiative muon capture on the proton in heavy baryon chiral perturbation theory
We have evaluated the amplitude for muon capture by a proton, mu + p --> n +
nu, to O(p^3) within the context of heavy baryon chiral perturbation theory
(HBChPT) using the new O(p^3) Lagrangian of Ecker and Mojzis (E&M). We obtain
expressions for the standard muon capture form factors and determine three of
the coefficients of the E&M Lagrangian, namely, b_7, b_{19}, and b_{23}. We
describe progress on the next step, a calculation of the radiative muon capture
process, mu + p --> n + nu + gamma.Comment: Talk at the 15th Int. Conf. on Few-Body Problems in Physics, 22-26
July, 1997, Groningen, The Netherlands, to be published in the proceedings; 5
pages, LaTeX, using espcrc1.st
Exploring nonlocal observables in shock wave collisions
We study the time evolution of 2-point functions and entanglement entropy in
strongly anisotropic, inhomogeneous and time-dependent N=4 super Yang-Mills
theory in the large N and large 't Hooft coupling limit using AdS/CFT. On the
gravity side this amounts to calculating the length of geodesics and area of
extremal surfaces in the dynamical background of two colliding gravitational
shockwaves, which we do numerically. We discriminate between three classes of
initial conditions corresponding to wide, intermediate and narrow shocks, and
show that they exhibit different phenomenology with respect to the nonlocal
observables that we determine. Our results permit to use (holographic)
entanglement entropy as an order parameter to distinguish between the two
phases of the cross-over from the transparency to the full-stopping scenario in
dynamical Yang-Mills plasma formation, which is frequently used as a toy model
for heavy ion collisions. The time evolution of entanglement entropy allows to
discern four regimes: highly efficient initial growth of entanglement, linear
growth, (post) collisional drama and late time (polynomial) fall off.
Surprisingly, we found that 2-point functions can be sensitive to the geometry
inside the black hole apparent horizon, while we did not find such cases for
the entanglement entropy.Comment: 28 pp, 9 figs; v2: updated references, changed color bars in Figure 2
and Figure
Power counting in baryon chiral perturbation theory including vector mesons
It is demonstrated that using a suitable renormalization condition one
obtains a consistent power counting in manifestly Lorentz-invariant baryon
chiral perturbation theory including vector mesons as explicit degrees of
freedom.Comment: 8 pages, REVTeX 4, 3 figure
Carroll black holes
Despite the absence of a lightcone structure, some solutions of Carroll
gravity show black hole-like behaviour. We define Carroll black holes as
solutions of Carroll gravity that exhibit Carroll thermal properties and have a
Carroll extremal surface, notions introduced in our work. The latter is a
Carroll analogue of a Lorentzian extremal surface. As examples, we discuss the
Carroll versions of Schwarzschild, Reissner-Nordstr\"om, and BTZ black holes
and black hole solutions of generic 1+1 dimensional Carroll dilaton gravity,
including Carroll JT and Carroll Witten black holes.Comment: 58pp, 7 fig
Rho meson properties from combining QCD-based models
Aiming at the calculation of the properties of rho-mesons, non-perturbative
QCD-based methods are discussed concerning their potentials as well as their
short-comings. The latter are overcome by combining these techniques. The
utilized methods are (i) the chiral constituent quark model deduced from the
instanton vacuum model and large-N_c arguments, (ii) chiral perturbation theory
unitarized by the inverse amplitude method and (iii) QCD sum rules. Advantages
of the combination of these methods are especially the absence of un-physical
quark-production thresholds and parameter-free results. Already in the chiral
limit and in leading order in 1/N_c one obtains a reasonable result for the
mass of the rho-meson, namely m_rho = 790 \pm 30 MeV. Using the KSFR relation
the universality of the rho-meson coupling is recovered. The latter is found to
be g = 6.0 \pm 0.3.Comment: 16 pages, 1 figure, Revtex
Muon capture by a proton in heavy baryon chiral perturbation theory
The matrix element for muon capture by a proton is calculated to O(p^3)
within heavy baryon chiral perturbation theory using the new O(p^3) Lagrangian
of Ecker and Mojzis. External nucleon fields are renormalized using the
appropriate definition of the wave function renormalization factor Z_N. Our
expression for Z_N differs somewhat from that found in existing literature, but
is the one which is consistent with the Lagrangian we use and the one which
ensures, within our approach, the nonrenormalization of the vector coupling as
required by the conserved vector current. Expressions for the standard muon
capture form factors are derived and compared to experimental data and we
determine three of the coefficients of the Ecker - Mojzis Lagrangian, namely,
b_7, b_{19}, and b_{23}.Comment: 14 pages, LaTeX, using revte
Comparison of intensity modulated radiotherapy (IMRT) with intensity modulated particle therapy (IMPT) using fixed beams or an ion gantry for the treatment of patients with skull base meningiomas
<p>Abstract</p> <p>Background</p> <p>To examine the potential improvement in treatment planning for patients with skull base meningioma using IMRT compared to carbon ion or proton beams with and without a gantry.</p> <p>Methods</p> <p>Five patients originally treated with photon IMRT were selected for the study. Ion beams were chosen using a horizontal beam or an ion gantry. Intensity controlled raster scanning and the intensity modulated particle therapy mode were used for plan optimization. The evaluation included analysis of dose-volume histograms of the target volumes and organs at risk.</p> <p>Results</p> <p>In comparison with carbon and proton beams only with horizontal beams, carbon ion treatment plans could spare the OARs more and concentrated on the target volumes more than proton and photon IMRT treatment plans. Using only a horizontal fixed beam, satisfactory plans could be achieved for skull base tumors.</p> <p>Conclusion</p> <p>The results of the case studies showed that using IMPT has the potential to overcome the lack of a gantry for skull base tumors. Carbon ion plans offered slightly better dose distributions than proton plans, but the differences were not clinically significant with established dose prescription concepts.</p
Complete Relativistic Description of the N*(1520)
A relativistic description of spin 3/2 resonances and their decay channels is
presented by calculating their selfenergies and spectral functions. The full
vector-spinor structure is taken into account. Special emphasis is put on the
N*(1520) and its decay channels pi N, rho N and pi \Delta. All interactions are
formulated such that only the correct number of degrees of freedom of a spin
3/2 state is propagated. The obtained results are compared with several
approximations frequently used to avoid the complicated vector-spinor
structure. Since this structure is taken fully into account here, the quality
of the approximations can be judged.Comment: 32 pages, 40 figure
Infrared renormalization of two-loop integrals and the chiral expansion of the nucleon mass
We describe details of the renormalization of two-loop integrals relevant to
the calculation of the nucleon mass in the framework of manifestly
Lorentz-invariant chiral perturbation theory using infrared renormalization. It
is shown that the renormalization can be performed while preserving all
relevant symmetries, in particular chiral symmetry, and that renormalized
diagrams respect the standard power counting rules. As an application we
calculate the chiral expansion of the nucleon mass to order O(q^6).Comment: Version accepted for publication in Nucl. Phys. A, missing one-loop
diagram added, minor changes in notation, discussion of results improve
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