118650221
Holonomies of gauge fields in twistor space 3: Gravity as a square of N=4 theory
Abstract In a recent paper, we show that an S-matrix functional for graviton amplitudes can be described by an N = 8 supersymmetric gravitational holonomy operator in twistor space. In this paper, we obtain an alternative expression for the gravitational holonomy operator such that it can be interpreted as a square of an N = 4 holonomy operator for frame fields, by taking a sum of certain shuffles over ordered indices. The new expression leads to amplitudes of not only spin-2 gravitons but also spin-0 massless particles. We discuss that the squared model is favored as a theory of quantum gravity.
14286968
An interpretation of multigraviton amplitudes
Abstract We obtain alternative expressions for the multigraviton tree level amplitudes and discuss their general properties. In particular, by analogy with Yang–Mills theory, we find that some combinatoric structure can be carried by a Chan–Paton factor of general relativity as a gauge theory.
119278846
Holonomies of gauge fields in twistor space 4: Functional MHV rules and one-loop amplitudes
Abstract We consider generalization of the Cachazo–Svrcek–Witten (CSW) rules to one-loop amplitudes of N = 4 super Yang–Mills theory in a recently developed holonomy formalism in twistor space. We first reconsider off-shell continuation of the Lorentz-invariant Nair measure for the incorporation of loop integrals. We then formulate an S-matrix functional for general amplitudes such that it implements the CSW rules at quantum level. For one-loop MHV amplitudes, the S-matrix functional correctly reproduces the analytic expressions obtained in the Brandhuber–Spence–Travaglini (BST) method. Motivated by this result, we propose a novel regularization scheme by use of an iterated-integral representation of polylogarithms and obtain a set of new analytic expressions for one-loop NMHV and N 2 MHV amplitudes in a conjectural form. We also briefly sketch how the extension to one-loop non-MHV amplitudes in general can be carried out.
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.
122644597
Quantum-Mechanical Study of the Landau-Zener Resonances in Nuclear Heavy-Ion Collisions
In order to resolve the well-known defects in classical or semi-classical approaches, we solve a two-state Landau-Zener problem fully quantum-mechanically with a localized radial coupling. An analytic expression of the T-matrix is derived by using distorted-wave Born approximation (DWBA). The convergence of the expansion formula is shown to be rapid enough for a reasonable range of the coilpling. The transition probabilities calculated with the formula are shown to well agree with those calculated by the coupled-channels method even for the strength of the coupling, which is five times as strong as that extracted from the two-center shell model. Therefore, the analytic DWBA formula is extremely useful for discussion of the Landau·Zener transition in nuclear heavy-ion collisions. Qualitative features of the resonancelike behaviour are discussed for three different forms of the coupling. For light systems such as 12C+170, the resonancelike structures are shown to survive in the excitation function even for a realistic finite range coupling, though the calculated cross sections are much reduced in comparison with those for a constant coupling in semi-classical calculations. For heavier systems such as 40Ca + 57 Ni, however, no resonancelike structure can survive because of the broad width resulting from the strong Coulomb potential.
14579423
Theory of fusion hindrance and synthesis of the superheavy elements
Abstract The two-step model for fusion reactions of massive systems is briefly reminded. By the use of fusion probabilities obtained by the model and of survival probabilities obtained by the new statistical code, we predict xn residue cross sections for 48 Ca+actinide systems leading to superheavy elements with Z=114, 116 and 118.
115177201
Perspectives of nuclear fission
18300734
Spin-Alignment and Quasi-Molecular Resonances in Heavy-Ion Collision
Fragment-fragment-$\gamma$ triple coincidence measurements of the $^{28}$Si~$+$~$^{28}$Si reaction at E$_{\rm c.m.}$~=~55.8 MeV, carefully chosen to populate a well known quasi-molecular resonance in $^{56}$Ni, have been performed at the VIVITRON tandem facility by using the Eurogam Phase~II $\gamma$-ray spectrometer. In the $^{28}$Si~$+$~$^{28}$Si reaction, the resonant behavior of the $^{28}$Si $+$ $^{28}$Si exit-channel is clearly observed by the present fragment-fragment coincidence data. The more unexpected result is the spin disalignment of the $^{28}$Si $+$ $^{28}$Si resonance. This has been demonstrated first by the measured angular distributions of the elastic 0$^{+}$, inelastic 2$^{+}$ and mutual excitation channels 2$^{+}-2^{+}$, which are dominated by a unique and pure partial wave with L = 38 ${\rm \hbar}$, and has been confirmed by measuring their particle-$\gamma$ angular correlations with Eurogam Phase II. The spin disalignment supports new molecular model predictions, in which the observed resonance would correspond to the ''Butterfly mode''. A discussion concerning the {\it spin alignment and spin disalignment} for different systems : $^{12}$C~$+$~$^{12}$C, $^{24}$Mg~$+$~$^{24}$Mg and $^{28}$Si~$+$~$^{28}$Si will be given.}
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