4,202 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
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
On the global symmetries of 6D superconformal field theories
We study global symmetry groups of six-dimensional superconformal field
theories (SCFTs). In the Coulomb branch we use field theoretical arguments to
predict an upper bound for the global symmetry of the SCFT. We then analyze
global symmetry groups of F-theory constructions of SCFTs with a
one-dimensional Coulomb branch. While in the vast majority of cases, all of the
global symmetries allowed by our Coulomb branch analysis can be realized in
F-theory, in a handful of cases we find that F-theory models fail to realize
the full symmetry of the theory on the Coulomb branch. In one particularly
mysterious case, F-theory models realize several distinct maximal subgroups of
the predicted group, but not the predicted group itself.Comment: 47 pages; v2: typos corrected, added the case su(6)* to the analysis
of section 5 and section 6.1. v3: references added, minor changes, published
versio
Supersymmetric predictions for the inclusive decay
We study the penguin induced transition in the minimal N=1
supersymmetric extension of the Standard Model with radiative breaking of the
electroweak group. We include the effects of one-loop corrections to the Higgs
potential and scalar masses. We show that the present upper and lower
experimental limits on the inclusive decay sharply constrain the parameter
space of the model in a wide range of values. The implications of
the recently advocated relation for the bilinear SUSY soft breaking
parameter in grand unified theories are also analyzed.Comment: 23 pages + 12 figures (hardcopies available on request), LATEX, SISSA
40/94/E
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
Decay and Supersymmetry
The inclusive radiative -decay is a sensitive probe of new physics,
especially if related to the virtual exchange of a charged Higgs boson.
Supersymmetric models provide a particularly interesting example. In the limit
of exact supersymmetry, BR()~=~0, due to the vanishing of any
magnetic-moment transition operator. We illustrate the impact of this
constraint for realistic values of the supersymmetry-breaking parameters.Comment: 7 pages, CERN-TH.6830/93 (Minor changes; a comment on the case >1 has been added
Fractional Branes and N=1 Gauge Theories
We discuss fractional D3-branes on the orbifold C^3/Z_2*Z_2. We study the
open and the closed string spectrum on this orbifold. The corresponding N=1
theory on the brane has, generically, a U(N_1)*U(N_2)*U(N_3)*U(N_4) gauge group
with matter in the bifundamental. In particular, when only one type of brane is
present, one obtains pure N=1 Yang-Mills. We study the coupling of the branes
to the bulk fields and present the corresponding supergravity solution, valid
at large distances. By using a probe analysis, we are able to obtain the
Wilsonian beta-function for those gauge theories that possess some chiral
multiplet. Although, due to the lack of moduli, the probe technique is not
directly applicable to the case of pure N=1 Yang-Mills, we point out that the
same formula gives the correct result also for this case.Comment: 21 pages, AMS-LaTeX, v2: references added and typos correcte
On CP Violation in Minimal Renormalizable SUSY SO(10) and Beyond
We investigate the role of CP phases within the renormalizable SUSY SO(10)
GUT with one 10_H, one 126bar_H one 126_H and one 210_H Higgs representations
and type II seesaw dominating the neutrino mass matrix. This framework is non
trivially predictive in the fermionic sector and connects in a natural way the
GUT unification of b and tau Yukawa couplings with the bi-large mixing scenario
for neutrinos. On the other hand, existing numerical analysis claim that
consistency with quark and charged lepton data prevents the minimal setup from
reproducing the observed CP violation via the Cabibbo-Kobayashi-Maskawa (CKM)
matrix. We re-examine the issue and find by inspection of the fermion mass sum
rules and a detailed numerical scan that, even though the CKM phase takes
preferentially values in the second quadrant, the agreement of the minimal
model with the data is actually obtained in a non negligible fraction of the
parameter space. We then consider a recently proposed renormalizable extension
of the minimal model, obtained by adding one chiral 120-dimensional Higgs
supermultiplet. We show that within such a setup the CKM phase falls naturally
in the observed range. We emphazise the robust predictivity of both models here
considered for neutrino parameters that are in the reach of ongoing and future
experiments.Comment: 9 pages, 6 figures. Two refs added, discussion expanded. To appear on
Phys. Rev.
Direct CP Violation in B->phi K_s and New Physics
In the presence of large New Physics contributions to loop-induced b->s
transitions, sizable direct CP violation in B-> phi K decays is expected on
general grounds. We compute explicitly CP-violating effects using QCD
factorization and find that, even in the restricted case in which New Physics
has the same penguin structure as the Standard Model, the rate asymmetry can be
of order one. We briefly discuss a more general scenario and comment on the
inclusion of power-suppressed corrections to factorization.Comment: 3 page
Anomalies and Tadpoles in Open/Closed String Duality
We discuss the role played by the divergences appearing in the interaction
between a fractional D3 brane dressed with an SU(N) gauge field and a stack of
N fractional D3 branes on the orbifolds C^2/Z_2 and C^3/(Z_2 x Z_2). In
particular we show that the logarithmic divergences in the closed string
channel, interpreted as due to twisted massless tadpoles, are mapped, under
open/closed string duality, in the logarithmic ones in the open string channel,
due to the massless states circulating in the annulus diagram and corresponding
to the one-loop divergences that one finds in the gauge theory living in the
world volume of the brane. This result provides a quantitative evidence of why
the chiral and scale anomalies of the supersymmetric and non conformal gauge
theories supported by the world volume of the branes can be inferred from
supergravity calculations.Comment: LaTeX, 8 pages. Contribution to the proceedings of the workshop of
the RTN Network "The quantum structure of space-time and the geometric nature
of fundamental interactions", Copenhagen, September 200
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