Destabilizing the gaugino condensate in modular invariant supergravity

We investigate the stability of the hidden sector gaugino condensate in a SL(2,Z)-invariant supergravity model inspired by the E8*E8 heterotic string, using the chiral superfield formalism. We calculate the Planck-suppressed corrections to the ``truncated approximation'' for the condensate value and the scalar potential. A transition to a phase with zero condensate occurs near special points in moduli space and at large compactification radius. We discuss the implications for the T-modulus dependence of supersymmetry-breaking.Comment: 12 pages, LaTeX, 3 ps figures; eq. 17 corrected, minor text changes, results unchange

Split Attractor Flow in N=2 Minimally Coupled Supergravity

We classify the stability region, marginal stability walls (MS) and split attractor flows for two-center extremal black holes in four-dimensional N=2 supergravity minimally coupled to n vector multiplets. It is found that two-center (continuous) charge orbits, classified by four duality invariants, either support a stability region ending on a MS wall or on an anti-marginal stability (AMS) wall, but not both. Therefore, the scalar manifold never contains both walls. Moreover, the BPS mass of the black hole composite (in its stability region) never vanishes in the scalar manifold. For these reasons, the "bound state transformation walls" phenomenon does not necessarily occur in these theories. The entropy of the flow trees also satisfies an inequality which forbids "entropy enigma" decays in these models. Finally, the non-BPS case, due to the existence of a "fake" superpotential satisfying a triangle inequality, can be treated as well, and it can be shown to exhibit a split attractor flow dynamics which, at least in the n=1 case, is analogous to the BPS one.Comment: 1+29 pages, 2 figures; v2: minor changes, especially in Sects. 1 and 2; Sect. 6 changed. To appear on NP

On the Seiberg-Witten map of N=2{\cal N}=2 SYM theory in Non(anti)commutative Harmonic Superspace

We consider ${\cal N}=2$ supersymmetric U(1) gauge theory in a nonanticommutative ${\cal N}=2$ harmonic superspace with the singlet deformation. We generalize analytic superfield and gauge parameter to the nonanticommutative theory so that gauge transformations act on the component fields in a canonical form (Seiberg-Witten map). This superfield, upon a field redefinition transforms under supersymmetry in a standard way.Comment: 10 pages, LaTe

String Quantum Symmetries and the SL(2,Z) Group

We prove, using arguments relying only on the "special K\"ahler" structure of the moduli space of the Calabi-Yau three-fold, that in the case of one single modulus the quantum modular group of the string effective action corresponding to Calabi-Yau vacua can not be SL(2,${Z\kern -4.6pt Z}$).Comment: 11 pages, Plain Tex, INFN-CA-93-1

Spontaneous Breaking of N=2 to N=1 in Rigid and Local Supersymmetric Theories

We analyze the relation between rigid and local supersymmetric N=2 field theories, when half of the supersymmetries are spontaneously broken. In particular, we show that the recently found partial supersymmety breaking induced by electric and magnetic Fayet-Iliopoulos terms in rigid theories can be obtained by a suitable flat limit of previously constructed N=2 supergravity models with partial super-Higgs in the observable sector.Comment: 9 pages, plain Late

Higgs and super-Higgs effects with naturally vanishing vacuum energy

We construct $N=1$ supergravity models where the gauge symmetry and supersymmetry are both spontaneously broken, with naturally vanishing classical vacuum energy and unsuppressed Goldstino components along gauge non-singlet directions. We discuss some physically interesting situations where such a mechanism could play a role, and identify the breaking of a grand-unified gauge group as the most likely possibility. We show that, even when the gravitino mass is much smaller than the scale $m_X$ of gauge symmetry breaking, important features can be missed if we first naively integrate out the degrees of freedom of mass ${\cal O} (m_X)$, in the limit of unbroken supersymmetry, and then describe the super-Higgs effect in the resulting effective theory. We also comment on possible connections with extended supergravities and realistic four-dimensional string constructions.Comment: 14 A4 pages, no figures, plain LATEX (no special macros, to be run twice

Orbits and Attractors for N=2 Maxwell-Einstein Supergravity Theories in Five Dimensions

BPS and non-BPS orbits for extremal black-holes in N=2 Maxwell-Einstein supergravity theories (MESGT) in five dimensions were classified long ago by the present authors for the case of symmetric scalar manifolds. Motivated by these results and some recent work on non-supersymmetric attractors we show that attractor equations in N=2 MESGTs in d=5 do indeed possess the distinct families of solutions with finite Bekenstein-Hawking entropy. The new non-BPS solutions have non-vanishing central charge and matter charge which is invariant under the maximal compact subgroup of the stabilizer of the non-BPS orbit. Our analysis covers all symmetric space theories G/H such that G is a symmetry of the action. These theories are in one-to-one correspondence with (Euclidean) Jordan algebras of degree three. In the particular case of N=2 MESGT with scalar manifold SU*(6)/USp(6) a duality of the two solutions with regard to N=2 and N=6 supergravity is also considered.Comment: Added a footnote on notation and comments on the attactor nature of non BPS solutions in section 5. Typos corrected. Version to appear in NPB. Latex file, 24 page

Compactifications of Type IIB Strings to Four Dimensions with Non-trivial Classical Potential

Type IIB strings are compactified on a Calabi-Yau three-fold. When Calabi-Yau-valued expectation values are given to the NS-NS and RR three-form field strengths, the dilaton hypermultiplet becomes both electrically and magnetically charged. The resultant classical potential is calculated, and minima are found. At singular points in the moduli space, such as Argyres-Douglas points, supersymmetric minima are found. A formula for the classical potential in $N=2$ supergravity is given which holds in the presence of both electric and magnetic charges.Comment: 32 pages REVTeX, no figure

Perturbative and Non-perturbative N =8 Supergravity

We study extremal black holes, their ADM mass and area of the horizon in N = 8 supergravity. Contrary to intuition gained from N = 2, 4 theories, in N = 8 supergravity BPS states may become massless only at the boundary of moduli space. We show that stringy states described in [1], which have no mass gap and survive in the toroidal compactification in addition to massless states of perturbative N = 8 supergravity, display a null singularity in four-dimensional space-time, when viewed as solutions of N = 8 Einstein equations. We analyze known methods of resolving such singularities and explain why they do not work in D=4, N = 8 supergravity. We discuss possible implications for the issue of UV finiteness of the four-dimensional N = 8 perturbation theory.Comment: 5p, few corrections and improvements, references added, published in Physics Letter

The Symplectic Structure of N=2 Supergravity and its Central Extension

We report on the formulation of $N=2$ $D=4$ supergravity coupled to $n_V$ abelian vector multiplets in presence of electric and magnetic charges. General formulae for the (moduli dependent) electric and magnetic charges for the $n_V+1$ gauge fields are given which reflect the symplectic structure of the underlying special geometry. The specification to Type IIB strings compactified on Calabi-Yau manifolds, with gauge group $U(1)^{h_{21}+1}$ is given.Comment: Contribution to the Proceedings of Trieste Conference on ``S Duality and Mirror Symmetry'', June 1995. LaTeX with espcrc2.sty (attached), 9 pg