121881632
Production and structure of light Sigma-hypernuclei
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.
18954226
Physical processes in naked singularity formation
Gravitational collapse is one of the most fruitful subjects in gravitational physics. It is well known that singularity formation is inevitable in complete gravitational collapse. It was conjectured that such a singularity should be hidden by horizons if it is formed from generic initial data with physically reasonable matter fields. Many possible counterexamples to this conjecture have been proposed over the past three decades, although none of them has proved to be sufficiently generic. In these examples, there appears a singularity that is not hidden by horizons. This singularity is called a `naked singularity.' The appearance of a naked singularity represents the formation of an observable high-curvature, strong-gravity region. In this paper we review examples of naked singularity formation and recent progress in research of observable physical processes - gravitational radiation and quantum particle creation - from a forming naked singularity.
121485803
Growth of primordial black holes
119448405
Birth of a timelike naked singularity
We investigate the causal structure of the Harada-Iguchi-Nakao (HIN)'s exact solution in detail, which describes the dynamical formation of naked singularity in the collapse of a regular spherical cluster of counterrotating particles. There are three kinds of radial null geodesics in the HIN spacetime. One is the regular null geodesics and the other two are the null geodesics which terminate at the singularity. The central massless singularity is timelike naked singularity and satisfies the strong curvature condition along the null geodesics except for the instant of singularity formation. The cluster dynamically asymptotes to the singular static Einstein cluster in which centrifugal force is balanced with gravity. The HIN solution provides an interesting example which demonstrates that collisionless particles invoke timelike naked singularity.
59582782
Accretion process onto super-spinning objects
The accretion process onto spinning objects in Kerr spacetimes is studied with numerical simulations. Our results show that accretion onto compact objects with Kerr parameter (characterizing the spin) |a| M is very different. In the superspinning case, for |a| moderately larger than M, the accretion onto the central object is extremely suppressed due to a repulsive force at short distance. The accreting matter cannot reach the central object, but instead is accumulated around it, forming a high density cloud that continues to grow. The radiation emitted in the accretion process will be harder and more intense than the one coming from standard black holes; e.g. {gamma}-rays could be produced as seen in some observations. Gravitational collapse of this cloud might even give rise to violent bursts. As |a| increases, a larger amount of accreting matter reaches the central object and the growth of the cloud becomes less efficient. Our simulations find that a quasisteady state of the accretion process exists for |a|/M > or approx. 1.4, independently of the mass accretion rate at large radii. For such high values of the Kerr parameter, the accreting matter forms a thin disk at very small radii. We provide some analytical argumentsmore » to strengthen the numerical results; in particular, we estimate the radius where the gravitational force changes from attractive to repulsive and the critical value |a|/M{approx_equal}1.4 separating the two qualitatively different regimes of accretion. We briefly discuss the observational signatures which could be used to look for such exotic objects in the Galaxy and/or in the Universe.« less
13993863
Causal structure of an inflating magnetic monopole
We clarify the causal structure of an inflating magnetic monopole. The spacetime diagram shows explicitly that this model is free from ``graceful exit'' problem, while the monopole itself undergoes ``eternal inflation''. We also discuss general nature of inflationary spacetimes.