1437149
Holographic Coulomb branch vevs
We compute holographically the vevs of all chiral primary operators for supergravity solutions corresponding to the Coulomb branch of = 4 SYM and find exact agreement with the corresponding field theory computation. Using the dictionary between 10d geometries and field theory developed to extract these vevs, we propose a gravity dual of a half supersymmetric deformation of = 4 SYM (on Mink4) by certain irrelevant operators.
14656683
Instanton symmetries and the entropy of compact manifolds
Many Euclidean Einstein manifolds possess continuous symmetry groups of at least one parameter and we consider here a classification scheme of $d$ dimensional compact manifolds based on the existence of such a one parameter group in terms of the fixed point sets of the isometries. We discuss applications of such a classification scheme, including the geometric interpretation of the entropy; there are intrinsic contributions to the entropy from the volumes of $(d-2)$ dimensional fixed point sets and contributions related to the cohomology structure of the orbit space of the isometry. We consider the relevance of such a decomposition of the entropy in the context of the no boundary proposal and cosmological processes, and generalise the discussion to compact solutions of gravity coupled to scalar and gauge fields.
12025810
Bulk charges in eleven dimensions
Eleven dimensional supergravity has electric type currents arising from the Chern-Simon and anomaly terms in the action. However the bulk charge integrates to zero for asymptotically flat solutions with topological trivial spatial sections. We show that by relaxing the boundary conditions to generalisations of the ALE and ALF boundary conditions in four dimensions one can obtain static solutions with a bulk charge. Solutions involving anomaly terms preserve between $1/16$ and $1/4$ of the supersymmetries but Chern-Simons fluxes generally break all of the remaining supersymmetry. One can introduce membranes with the same sign of charge into these backgrounds. This raises the possibility that these generalized membranes might decay quantum mechanically to leave just a bulk distribution of charge. Alternatively and more probably, a bulk distribution of charge can decay into a collection of singly charged membranes. Dimensional reductions of these solutions lead to novel representations of extreme black holes in four dimensions with up to four charges. We discuss how the eleven-dimensional Kaluza-Klein monopole wrapped around a space with non-zero first Pontryagin class picks up an electric charge proportional to the Pontryagin number.
18758701
Evolution of near-extremal black holes
Near extreme black holes can lose their charge and decay by the emission of massive BPS charged particles. We calculate the greybody factors for low energy charged and neutral scalar emission from four and five dimensional near extremal Reissner-Nordstrom black holes. We use the corresponding emission rates to obtain ratios of the rates of loss of excess energy by charged and neutral emission, which are moduli independent, depending only on the integral charges and the horizon potentials. We consider scattering experiments, finding that evolution towards a state in which the integral charges are equal is favoured, but neutral emission will dominate the decay back to extremality except when one charge is much greater than the others. The implications of our results for the agreement between black hole and D-brane emission rates and for the information loss puzzle are then discussed.
15434486
Higher dimensional Taub-Bolt solutions and the entropy of non compact manifolds
We discuss the action of a circle isometry group on non compact Euclidean Einstein manifolds. We discuss approaches to a decomposition of the action and entropy for non compact manifolds in terms of the characteristics of the orbit space of a suitable isometry. There is entropy associated with non trivial cohomology of the orbit space of the isometry, and we consider a class of non compact solutions for which such contributions do not vanish. To obtain suitable solutions we generalise the Bais-Batenburg construction of higher dimensional Taub-Nut type solutions to obtain the corresponding bolt solutions. We consider the generalisations to non compact solutions of gravity coupled to scalar and gauge fields.
6756135
Semiclassical stability of supergravity vacua
We discuss the existence of instantonic decay modes which would indicate a semiclassical instability of the vacua of 10- and 11-dimensional supergravity theories. Decay modes whose spin structures are incompatible with those of supersymmetric vacua have previously been constructed, and we present generalizations including those involving nontrivial dilaton and antisymmetric tensor fields. We then show that the requirement that any instanton describing supersymmetric vacuum decay should admit both a zero momentum hypersurface from which we describe the subsequent Lorentzian evolution and a spin structure at infinity compatible with the putative vacuum excludes all such decay modes, except those with unphysical energy-momentum tensors which violate the dominant energy condition. {copyright} {ital 1997} {ital The American Physical Society}
120317800
First {$\gamma$}-ray spectroscopy of Fe49 and Ni53: Isospin-breaking effects at large proton excess
Isospin-breaking effects have been studied for the first time in T=(3/2) isobaric analog states. Gamma decays have been observed from T{sub z}=-(3/2) nuclei, {sup 49}Fe and {sup 53}Ni, presented here in new level schemes, and mirror energy differences have been computed following observation of analog states in {sup 49}V and {sup 53}Mn, respectively. Shell-model calculations in the fp shell are in good agreement with the data and reveal the importance of non-Coulomb isospin-breaking effects in T=(3/2) isobaric analog states. A two-step fragmentation process was developed to allow access to highly proton-rich nuclei and to produce each member of a mirror pair via mirrored fragmentation of a {sup 56}Ni secondary beam. This work represents the first study using this technique and demonstrates the power of this approach for future studies of isobaric analog states in very proton-rich systems.
4343966
Evidence for a spin-aligned neutron–proton paired phase from the level structure of 92Pd
Shell structure and magic numbers in atomic nuclei were generally explained by pioneering work that introduced a strong spin–orbit interaction to the nuclear shell model potential. However, knowledge of nuclear forces and the mechanisms governing the structure of nuclei, in particular far from stability, is still incomplete. In nuclei with equal neutron and proton numbers (N = Z), enhanced correlations arise between neutrons and protons (two distinct types of fermions) that occupy orbitals with the same quantum numbers. Such correlations have been predicted to favour an unusual type of nuclear superfluidity, termed isoscalar neutron–proton pairing, in addition to normal isovector pairing. Despite many experimental efforts, these predictions have not been confirmed. Here we report the experimental observation of excited states in the N = Z = 46 nucleus 92Pd. Gamma rays emitted following the 58Ni(36Ar,2n)92Pd fusion–evaporation reaction were identified using a combination of state-of-the-art high-resolution γ-ray, charged-particle and neutron detector systems. Our results reveal evidence for a spin-aligned, isoscalar neutron–proton coupling scheme, different from the previous prediction. We suggest that this coupling scheme replaces normal superfluidity (characterized by seniority coupling) in the ground and low-lying excited states of the heaviest N = Z nuclei. Such strong, isoscalar neutron–proton correlations would have a considerable impact on the nuclear level structure and possibly influence the dynamics of rapid proton capture in stellar nucleosynthesis.
122430943
Spectroscopy of Nuclei Approaching the Proton Drip-line Using a Secondary-fragmentation Technique with the RISING Detector Array
An experiment utilizing a double fragmentation reaction was performed to study isobaric analogue states in A similar to 50 nuclei approaching the proton drip-line. gamma-ray spectroscopy will be used to identify excited states in the neutron-deficient nuclei produced in the second fragmentation reaction. Excited state level schemes will be obtained, through comparison with states in their well-known mirror partners, along with information on Coulomb effects through measurements of the Coulomb energy differences between isobaric analogue excited states. The validity of isospin symmetry for nuclei approaching the proton drip-line can also be investigated and the information gained will aid in testing and improving fp shell model calculations. The analysis of the collected data is at a preliminary stage and current status of this work is reported.
123206542
First Gamma-Ray Spectroscopy and Isospin Symmetry Study of the N = Z-2 Nucleus V-44
Excited states in the T-z = -1 nucleus V-44 have been observed for the first time. The states have been identified through recoil-gamma-gamma coincidences and comparison with analogue states in the mirror nucleus Sc-44. Mirror energy differences have been extracted and compared to state-of-the-art fp shell-model calculations which include charge symmetry breaking forces.
120497533
Isobaric Analogue States Studied in Mirrored Fragmentation and Knockout Reactions
A Gamma-ray spectroscopic study of excited states of isobaric multiplets has been performed in recent years, with a view to gaining a quantitative understanding of energy differences between excited states in terms of a range of Coulomb and other isospin breaking phenomena. Recently, the experimental programme has been augmented by a study of isobaric analogue states of mirror nuclei populated in mirrored fragmentation reactions. In this presentation, recent results on the $T =\frac{3}{2}$ analogue states in the $T_z =\pm \frac{3}{2}$ mirror pair 53Ni/53Mn will be summarised. In this work, further strong evidence is found for the need to include an anomalous isospin-breaking two-body matrix element for angular-momentum couplings of J = 2, in addition the expected Coulomb contribution, in order to account for the experimental data.