118332512
Isospin Properties of (K-, N) Reactions for the Formation of Deeply-bound Antikaonic Nuclei
Abstract The formation of deeply-bound antikaonic K − / K ¯ 0 nuclear states in nuclear ( K − , N ) reactions is investigated theoretically within a distorted-wave impulse approximation (DWIA), considering the isospin properties of the Fermi-averaged K − + N → N + K ¯ elementary amplitudes. We calculate the formation cross sections of the deeply-bound K ¯ states by the ( K − , N ) reactions on the nuclear targets, 12C and 28Si, at incident K − lab momentum p K − = 1.0 GeV / c and θ lab = 0 ° , introducing a complex effective nucleon number N eff for unstable bound states in the DWIA. The results show that the deeply-bound K ¯ states can be populated dominantly by the ( K − , n ) reaction via the total isoscalar Δ T = 0 transition owing to the isospin nature of the K − + N → N + K ¯ amplitudes, and that the cross sections described by Re N eff and Arg N eff enable to deduce the structure of the K ¯ nuclear states; the calculated inclusive nucleon spectra for a deep K ¯ -nucleus potential do not show distinct peak structure in the bound region. The few-body K ¯ ⊗ [ N N ] and K ¯ ⊗ [ N N N ] states formed in ( K − , N ) reactions on s-shell nuclear targets, 3He, 3H and 4He, are also discussed.
123245410
Neutron-rich Hypernuclei
Abstract Production and spectroscopy of neutron-rich Λ hypernuclei by double-charge exchange reactions ( π − , K + ) on nuclear targets are investigated in a theoretical viewpoint. The Λ–Σ coupling in nuclei induces a Σ admixture, which is enhanced in a neutron-excess environment, and plays an important role in production by a one-step mechanism π − p → K + Σ − via Σ − doorways in these reactions. A feasibility of extracting the Σ − admixture probability in the neutron-rich 10ΛLi hypernucleus by the 10B( π − , K + ) reaction is examined within a distorted-wave impulse approximation.
119341375
Calculation of the 3He (in-flight K−,n) reaction for searching the deeply-bound K−pp state
Abstract The formation of a deeply-bound K − p p state by the 3 He (in-flight K − , n ) reaction is investigated theoretically in the distorted-wave impulse approximation using the Green's function method. The expected inclusive and semi-exclusive spectra at p K − = 1.0 GeV / c and θ n = 0 ° are calculated for the forthcoming J-PARC E15 experiment. We employ optical potentials between the K − and “ pp ” core-nucleus, and demonstrate systematically the dependence of the spectral shape on V 0 and W 0 , which are the real and imaginary parts of the strength for the optical potential, respectively. The necessary condition to observe a distinct peak of the K − p p bound state with I = 1 / 2 , J π = 0 − in the spectrum turns out to be that the value of V 0 is deeper than ∼ − 100 MeV and W 0 shallower than ∼ − 100  MeV , of which the strength parameters come up to recent theoretical predictions.
95195670
Structures and productions of typical sd-shell hypernuclei in shell-model calculations
As one of the typical sd-shell hypernuclei, the positive- and negative-parity energy levels of 20ΛNe are calculated to investigate structures of low-lying states within the shell model calculations. In addition to the conventional NN effective interactions, the ΛN G-matrix interactions derived from the Nijmegen NSC97f potentials are employed. The production cross sections of (π+,K+) and (K−,π−) reactions are estimated using the calculated shell-model wave functions.
119490437
Have we already detected astrophysical symptoms of space-time noncommutativity?
We discuss astrophysical implications of $\kappa$-Minkowski space-time, in which there appears space-time noncommutativity. We first derive a velocity formula for particles based on the motion of a wave packet. The result is that a massless particle moves at a constant speed as in the usual Minkowski space-time, which implies that an arrival time analysis by $\gamma$-rays from Markarian (Mk) 421 does not exclude space-time noncommutativity. Based on this observation, we analyze reaction processes in $\kappa$-Minkowski space-time which are related to the puzzling detections of extremely high-energy cosmic rays above the Greisen-Zatsepin-Kuzmin cutoff and of high-energy ($\sim$20 TeV) $\gamma$-rays from Mk 501.
119375284
Is there a black hole minimum mass
Applying the first and generalized second laws of thermodynamics for a realistic process of near critical black hole formation, we derive an entropy bound, which is identical to Bekenstein's one for radiation. Relying upon this bound, we derive an absolute minimum mass $\ensuremath{\sim}0.04\sqrt{{g}_{*}}{m}_{\mathrm{Pl}}$, where ${g}_{*}$ and ${m}_{\mathrm{Pl}}$ is the effective degrees of freedom for the initial temperature and the Planck mass, respectively. Since this minimum mass coincides with the lower bound on masses of which black holes can be regarded as classical against the Hawking evaporation, the thermodynamical argument will not prohibit the formation of the smallest classical black hole. For more general situations, we derive a minimum mass, which may depend on the initial value for entropy per particle. For primordial black holes, however, we show that this minimum mass can not be much greater than the Planck mass at any formation epoch of the Universe, as long as ${g}_{*}$ is within a reasonable range. We also derive a size-independent upper bound on the entropy density of a stiff fluid in terms of the energy density.
119219189
High-speed collapse of a hollow sphere of type I matter
In this paper, we study the dynamics of a hollow spherical matter collapsing with a very large initial velocity. The spacetime is initially very similar to the Vaidya solution, and the deviations from this background are treated perturbatively. The equations of state for radial pressure pR = kρ and tangential one pT = wρ with constants k and w are assumed. We find for the case of equations of state k < 1 and 0 < w ≤ 1 that the initial velocity, which is nearly the speed of light, is strongly decelerated. This result implies that the pressure is essential to the property of singularity formation in gravitational collapse even for initially nearly light-speed collapse. By contrast, in cases with the negative tangential pressure, the present result implies that the central naked singularity similar to that of the Vaidya spacetime can be formed, even though the radial pressure is positive, and the weak, strong and dominant energy conditions hold. Especially, in the case of w < −(1 − k)/4, the high-speed collapse will produce the spacetime structure very similar to that of the Vaidya spacetime.
118942084
Gravitational waves around a naked singularity: Odd - parity perturbation of Lemaitre-Tolman-Bondi space-time
The motion of a spherical dust cloud is described by the Lemaitre-Tolman-Bondi solution and is completely specified by initial values of distributions of the rest mass density and specific energy of the dust fluid. 
From generic initial conditions of this spherically symmetric collapse, there appears a naked singularity at the symmetric center in the course of the gravitational collapse of the dust cloud. So this might be a counter example to the cosmic censorship hypothesis. To investigate the genericity of this example, we examine the stability of the `nakedness' of this singularity against odd-parity modes of non-spherical linear perturbations for the metric, i.e., linear gravitational waves. We find that the perturbations do not diverge but are well-behaved even in the neighborhood of the central naked singularity. This means that the naked singularity formation process is marginally stable against the odd-parity modes of linear gravitational waves.