6,009 research outputs found

### N=1 Super QCD and Fractional Branes

We show how to get the one-loop beta function and the chiral anomaly of N=1
Super QCD from a stack of fractional N D3-branes localized inside the
world-volume of 2M fractional D7-branes on the orbifold C^3/(Z_2 x Z_2). They
are obtained by analyzing the classical supergravity background generated by
such a brane configuration, in the spirit of the gauge/gravity correspondence.Comment: 4 pages, LaTeX. Talk given at the IXth International Symposium on
Particles, Strings and Cosmology PASCOS '03, Mumbai-India, January 3-8 2003.
To appear in a special issue of Praman

### D3-branes dynamics and black holes

Using the D3-brane as the fundamental tool, we adress two aspects of D-branes
physics. The first regards the interaction between two electromagnetic dual
D-branes in 10 dimensions. In particular, we give a meaning to {\it both} even
and odd spin structure contributions, the latter being non vanishing for non
zero relative velocity $v$ (and encoding the Lorentz-like contribution). The
second aspect regards the D-brane/black holes correspondence. We show how the 4
dimensional configuration corresponding to a {\it single} D3-brane wrapped on
the orbifold T^6/Z_3 represents a regular Reissner-Nordstrom solution of d=4
N=2 supergravityComment: 8 pages, latex, 1 eps figure. Talk presented by M. Bertolini at the
conference "Quantum aspects of gauge theories, supergravity and unification"
in Corfu`; to appear in the proceeding

### More Anomalies from Fractional Branes

In this note we show how the anomalies of both pure and matter coupled N=1,2
supersymmetric gauge theories describing the low energy dynamics of fractional
branes on orbifolds can be derived from supergravity.Comment: 11 pages, latex; v2: minor typos fixe

### N=8 BPS black holes preserving 1/8 supersymmetry

In the context of N=8 supergravity we consider BPS black-holes that preserve
1/8 supersymmetry. It was shown in a previous paper that, modulo U-duality
transformations of E_{7(7)} the most general solution of this type can be
reduced to a black-hole of the STU model. In this paper we analize this
solution in detail, considering in particular its embedding in one of the
possible Special K\"ahler manifold compatible with the consistent truncations
to N=2 supergravity, this manifold being the moduli space of the T^6/Z^3
orbifold, that is: SU(3,3)/SU(3)*U(3). This construction requires a crucial use
of the Solvable Lie Algebra formalism. Once the group-theoretical analisys is
done, starting from a static, spherically symmetric ans\"atz, we find an exact
solution for all the scalars (both dilaton and axion-like) and for gauge
fields, together with their already known charge-dependent fixed values, which
yield a U-duality invariant entropy. We give also a complete translation
dictionary between the Solvable Lie Algebra and the Special K\"ahler formalisms
in order to let comparison with other papers on similar issues being more
immediate. Although the explicit solution is given in a simplified case where
the equations turn out to be more manageable, it encodes all the features of
the more general one, namely it has non-vanishing entropy and the scalar fields
have a non-trivial radial dependence.Comment: 29+1 pages, 1 Latex file; a misprint in the entropy formula,
eq.(5.14), correcte

### Worldsheet instantons and (0,2) linear models

We study the stability of heterotic compactifications described by (0,2)
gauged linear sigma models with respect to worldsheet instanton corrections to
the space-time superpotential following the work of Beasley and Witten. We show
that generic models elude the vanishing theorem proved there, and may not
determine supersymmetric heterotic vacua. We then construct a subclass of
linear models for which a vanishing theorem holds, generating an extensive list
of consistent heterotic backgrounds.Comment: 21 pages; v2: minor correction

### A focus on focal surfaces

We make a systematic study of the focal surface of a congruence of lines in
the projective space. Using differential techniques together with techniques
from intersection theory, we reobtain in particular all the invariants of the
focal surface (degree, class, class of its hyperplane section, sectional genus
and degrees of the nodal and cuspidal curve). We study in particular the
congruences of chords to a smooth curve and the congruences of bitangents or
flexes to a smooth surface. We find that they possess unexpected components in
their focal surface, and conjecture that they are the only ones with this
property.Comment: Plain TeX, 33 pages with no figure

### N=2 four-dimensional gauge theories from fractional branes

This is a pedagogical and extended version of the results published in Refs.
[1,2] and presented by the authors in various talks during the last year. We
discuss the type II D-branes (both regular and fractional) of the orbifold
R^{1,5}*R^4/Z_2, we determine their corresponding supergravity solution and
show how this can be used to study the properties of N=2 super Yang-Mills.
Supergravity is able to reproduce the perturbative moduli space of the gauge
theory, while it does not encode the non-perturbative corrections. The short
distance region of space-time, which corresponds to the infrared region of the
gauge theory, is excised by an enhancon mechanism, and more states should be
included in the low energy effective action in order to enter inside the
enhancon and recover the instanton corrections. (To be published on a Memorial
Volume commemorating Michael Marinov)Comment: 44 pages, AMS-LaTeX, no figure

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