37143222
PARTICLE EMISSION BUT ALSO FISSION IN THE DECAY OF VERY EXCITED NUCLEI
An extension of the s tat is t ica l model for the study of very excited nuclei is presented. The temperature and angular momentum dependences of the fission barriers are obtained in a l iqu id drop picture. I t provides us with the relevant potential landscapes for some col lect ive variables which evolve during the decay according to a generalized transport equation. The l i gh t part ic le evaporation during the fast f ission process and the f ission after compound nucleus formation is calculated and compared with some available experimental results, e.g. for '•"Ar + U at 27 MeV/u. The competing process of part ic le emission (cooling) during the thermal equilibrium prevents a complete transfer of excitation energy along the whole evolution of the system. Such nuclei should be called warm instead of hot.
28272098
Diffusion over a saddle with a langevin equation
The diffusion problem over a saddle is studied using a multidimensional Langevin equation. An analytical solution is derived for a quadratic potential and the probability to pass over the barrier deduced. A very simple solution is given for the one-dimensional problem and a general scheme is shown for higher dimensions.
121916152
On stochastic approaches of nuclear dynamics
Abstract We present recent developments of stochastic descriptions of nuclear dynamics. We focus on the newly introduced microscopic descriptions, such as stochastic extensions of currently used kinetic equations, as well as on more phenomenological, macroscopic approaches. We show to what extent these stochastic descriptions may offer a proper picture of nuclear dynamics both in strongly out of equilibrium situations, such as the ones encountered in energetic heavy-ion collisions or in closer to equilibrium situations such as the deexcitation of hot nuclei by thermal fission. In Section 1 we present a pedestrian introduction to the stochastic description of dynamical systems. We start from the elementary Brownian motion and introduce the Langevin and Fokker-Planck descriptions of the motion on that occasion. A few words are then spent to discuss the numerical methods developed for simulating stochastic equations. Section 2 of the paper is devoted to a formal introduction and discussion of both macroscopic and microscopic stochastic descriptions of nuclear dynamics. After a brief introduction reminding general concepts of equilibrium statistical physics we focus on microscopic descriptions of the many-body problem. We introduce here the Boltzmann Langevin equation which will provide a basis for many subsequent discussions. After having discussed the obtention of this equation from various points of view (from density matrix and Green's function techniques in particular), we consider reduced versions of this equation as well as a Fokker-Planck alternative. Section 3 is devoted to an analysis of fission by means of Langevin or Fokker-Planck-like approaches. We mainly discuss phenomenological approaches and spend some time in a detailed presentation of the ingredients entering these models. We present results obtained in these dynamical calculations when a proper account of particle evaporation is included for describing the fission of hot nuclei. Critical comparisons with experimental data are also provided. In Section 4 we focus on the application of the Boltzmann Langevin Equation to various situations encountered in energetic nuclear collisions. We first remind some typical examples for which this stochastic approach is both necessary and well suited. Typical applications are nuclear multifragmentation and subthreshold particle production, such as in particular kaon production. We discuss possible simulations of this equation and present some results in realistic calculations of collisions. We particularly focus on the dynamics of collective variables such as the quadrupole moment of the momentum distribution. We finally discuss other numerical simulations developed in the field. The last section before conclusion is devoted to extensions presently developed in the field of microscopic stochastic descriptions of nuclear dynamics. We present as a first step a relativistic version of the theory, then focus on fluid dynamics reductions. We finally discuss in some detail the recently introduced Stochastic time-dependent Hartree-Fock theory, which could provide new interesting developments.
120154304
Evidence for nuclear Landau-Zener effect: New resonance mechanism in heavy-ion reactions
Characteristic resonancelike peaks recently observed in the angle-integrated inelastic cross sections for the /sup 13/C-/sup 17/O system are understood in terms of the Landau-Zener excitation mechanism at energy level crossings. Angle-integrated inelastic cross sections estimated with the Landau-Zener formula show a series of resonancelike peaks as a function of incident energy, each of which is associated with a grazing angular momentum of the relative motion between nuclei. Simple expressions are given for resonance energies and ''widths'' of new ''resonances.'' This resonance mechanism is a new one, which has not been known in nuclear reactions nor in atomic collisions, although it is based on the well-known Landau-Zener promotion mechanism.
122223146
Limitation on heavy ion fusion and nuclear level density at high excitation energies
Over a wide energy range, the limitation on fusion is interpreted from the properties of the compound nuclear level density obtained by taking into account the finiteness of the nucleus. The essential point is to use the shell model single particle bound states in the calculation of the grand partition function. The critical angular momentum for fusion is estimated in connection with the critical temperature for fusion.
123157220
A Molecular Model for High-Spin Heavy-Ion Resonances
A new molecular model is presented in detail, in which collective motions of the di-nuclear system are described in the rotating molecular frame. The model is applied to high-spin resonances observed in 24 Mg + 24 Mg scattering. A stable configuration of the system is found to be a pole-pole one, due to the prolate shape of the 24 Mg nuclei. Normal modes at the equilibrium are solved to give rise to various molecular levels, which appear to be in good correspondence with the experiment
119304812
Application of abelian holonomy formalism to the elementary theory of numbers
We consider an abelian holonomy operator in two-dimensional conformal field theory with zero-mode contributions. The analysis is made possible by use of a geometric-quantization scheme for abelian Chern-Simons theory on S1 × S1 × R. We find that a purely zero-mode part of the holonomy operator can be expressed in terms of Riemann's zeta function. We also show that a generalization of linking numbers can be obtained in terms of the vacuum expectation values of the zero-mode holonomy operators. Inspired by mathematical analogies between linking numbers and Legendre symbols, we then apply these results to a space of Fp = Z/pZ, where p is an odd prime number. This enables us to calculate “scattering amplitudes” of identical odd primes in the holonomy formalism. In this framework, the Riemann hypothesis can be interpreted by means of a physically obvious fact, i.e., there is no notion of “scattering” for a single-particle system. Abelian gauge theories described by the zero-mode holonomy operators will be usef...
14986084
Holonomies of gauge fields in twistor space 1: Bialgebra, supersymmetry, and gluon amplitudes
Abstract We introduce a notion of holonomy in twistor space and construct a holonomy operator by use of a spinor-momenta formalism in twistor space. The holonomy operator gives a monodromy representation of the Knizhnik–Zamolodchikov (KZ) equation, which is mathematically equivalent to a linear representation of a braid group. We show that an S-matrix functional for gluon amplitudes can be expressed in terms of a supersymmetric version of the holonomy operator. A variety of mathematical and physical concepts, such as integrability, general covariance, Lorentz invariance and Yangian symmetry, are knit together by the holonomy operator. These results shed a new light on gauge theories in four-dimensional spacetime.
44215083
Fuzzy S(4) and its construction
We present construction of fuzzy S, utilizing the fact that CP is an S bundle over S. Fuzzy S is obtained by imposing an additional algebraic constraint on fuzzy CP. Hence, as in the case of fuzzy CP = SU(4)/U(3), fuzzy S is globally defined on R with the additional constraint on top of the construction of fuzzy CP. We consider the commutative limit of fuzzy S and find that it naturally gives commutative S in terms of homogeneous coordinates on CP. We also discuss exact matrix-function correspondence of fuzzy S. In conclusion, it is proposed that fuzzy S is described by a certain form of block-diagonal matrix whose embedding square matrix represents fuzzy CP.
119406982
Emergence of longitudinal 7-branes and fuzzy S 4 in compactification scenarios of M(atrix) theory
In M(atrix) theory, there exist membranes and longitudinal 5-branes (L5-branes) as extended objects. Transverse components of these brane solutions are known to be described by fuzzy ${\mathbf{C}\mathbf{P}}^{k}$ ($k=1$, 2), where $k=1$ and $k=2$ correspond to spherical membranes and L5-branes of ${\mathbf{C}\mathbf{P}}^{2}\ifmmode\times\else\texttimes\fi{}{S}^{1}$ world-volume geometry, respectively. In addition to these solutions, we here show the existence of L7-branes of ${\mathbf{C}\mathbf{P}}^{3}\ifmmode\times\else\texttimes\fi{}{S}^{1}$ geometry, introducing extra potentials to the M(atrix) theory Lagrangian. As in the cases of $k=1$, 2, the L7-branes (corresponding to $k=3$) also break the supersymmetries of M(atrix) theory. The extra potentials are introduced such that the energy of a static L7-brane solution becomes finite in the large $N$ limit where $N$ represents the matrix dimension of fuzzy ${\mathbf{C}\mathbf{P}}^{3}$. As a consequence, fluctuations from the L7-branes are suppressed, which effectively describes compactification of M(atrix) theory down to 7 dimensions. We show that one of the extra potentials can be considered as a matrix-valued 7-form. The presence of the 7-form in turn supports a possibility of Freund-Rubin type compactification. This suggests that our modification of M(atrix) theory can also lead to a physically interesting matrix model in four dimensions. In hope of such a possibility, we further consider compactification of M(atrix) theory down to fuzzy ${S}^{4}$ which can be defined in terms of fuzzy ${\mathbf{C}\mathbf{P}}^{3}$. Along the way, we also find a new L5-brane solution to M(atrix) theory which has purely spherical geometry in the transverse directions.
18483460
Multigluon amplitudes , N = 4 constraints and the WZW model
Classical N = 4 Yang-Mills theory is defined by the superspace constraints. We obtain a solution of a subset of these constraints and show that it leads to the maximally helicity violating (MHV) amplitudes. The action which leads to the solvable part of the constraints is a Wess-Zumino-Witten (WZW) action on a suitably extended superspace. The non-MHV tree amplitudes can also be expressed in terms of this action.