13,411 research outputs found

### Discrimination of $\Sigma$-nucleus potentials in the angular distribution of elastic scattering of $\Sigma^-$ hyperons from nuclei

We theoretically investigate the elastic scattering of 50-MeV $\Sigma^-$
hyperons from $^{28}$Si and $^{208}$Pb in order to clarify the radial
distribution of $\Sigma$-nucleus (optical) potentials. The angular
distributions of differential cross sections are calculated using several
potentials that can explain experimental data of the $\Sigma^-$ atomic X-ray
and ($\pi^-$, $K^+$) reaction spectra simultaneously. The magnitude and
oscillation pattern of the angular distributions are understood by the use of
nearside/farside decompositions of their scattering amplitudes. It is shown
that the resultant angular distributions can considerably discriminate among
the radial distributions of the potentials that have a repulsion inside the
nuclear surface and an attraction outside the nucleus with a sizable
absorption

### Heavy-light meson in anisotropic lattice QCD

We examine whether the $O(a)$ improved quark action on anisotropic lattices
can be used as a framework for the heavy quark, which enables precision
computation of matrix elements of heavy-light mesons. To this end, it is
crucial to verify that a mass independent and nonperturbative tuning of the
parameters is possible. As a first step, we observe the dispersion relation of
heavy-light mesons on a quenched lattice using the action which is
nonperturbatively tuned only for the leading terms. On a lattice with the
spatial cutoff $a_\sigma^{-1} \simeq$ 1.6 GeV and the anisotropy $\xi=4$, the
relativity relation holds within 2% accuracy in the quark mass region $a_\sigma
m_Q \leq 1.2$ with the bare anisotropy parameter tuned for the massless quark.
We also apply the action to a calculation of heavy-light decay constants in the
charm quark mass region.Comment: Lattice2002(heavyquark), 3 pages, 2 figure

### Newtonian Analysis of Gravitational Waves from Naked Singularity

Spherical dust collapse generally forms a shell focusing naked singularity at
the symmetric center. This naked singularity is massless. Further the Newtonian
gravitational potential and speed of the dust fluid elements are everywhere
much smaller than unity until the central shell focusing naked singularity
formation if an appropriate initial condition is set up. Although such a
situation is highly relativistic, the analysis by the Newtonian approximation
scheme is available even in the vicinity of the space-time singularity. This
remarkable feature makes the analysis of such singularity formation very easy.
We investigate non-spherical even-parity matter perturbations in this scheme by
complementary using numerical and semi-analytical approaches, and estimate
linear gravitational waves generated in the neighborhood of the naked
singularity by the quadrupole formula. The result shows good agreement with the
relativistic perturbation analysis recently performed by Iguchi et al. The
energy flux of the gravitational waves is finite but the space-time curvature
carried by them diverges.Comment: 23 pages, 8 figure

### A Reversibility Parameter for a Markovian Stepper

Recent experimental studies on the stepwize motion of biological molecular
motors have revealed that the ``characteristic distance'' of a step is usually
less than the actual step size. This observation implies that the
detailed-balance condition for kinetic rates of steps is violated in these
motors. In this letter, in order to clarify the significance of the
characteristic distance, we study a Langevin model of a molecular motor with a
hidden degree of freedom. We find that the ratio of the characteristic distance
to the step size is equal to unity if the dominant paths in the state space are
one dimensional, while it deviates from unity if the dominant paths are
branched. Therefore, this parameter can be utilized to determine the
reversibility of a motor even under a restricted observation.Comment: 6 pages, 2 figures - minor revision

### Analytic derivation of the map of null rays passing near a naked singularity

Recently the energy emission from a naked singularity forming in spherical
dust collapse has been investigated. This radiation is due to the particle
creation in a curved spacetime. In this discussion, the central role is played
by the mapping formula between the incoming and the outgoing null coordinates.
For the self-similar model, this mapping formula has been derived analytically.
But for the model with $C^{\infty}$ density profile, the mapping formula has
been obtained only numerically. In the present paper, we argue that the
singular nature of the mapping is determined by the local geometry around the
point at which the singularity is first formed. If this is the case, it would
be natural to expect that the mapping formula can be derived analytically. In
the present paper, we analytically rederive the same mapping formula for the
model with $C^{\infty}$ density profile that has been earlier derived using a
numerical technique.Comment: 4 pages, submitted to Phys. Rev.

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