2,653 research outputs found
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
On CP-Odd Effects in K_L \to 2\pi and K^{\pm} \to \pi^{\pm} \pi^{\pm} \pi^{\mp} Decays Generated by Direct CP Violation
The amplitudes of the K^{\pm} \to 3\pi and K \to 2\pi decays are expressed in
terms of different combinations of one and the same set of CP-conserving and
CP-odd parameters. Extracting the magnitudes of these parameters from the data
on K \to 2\pi decays, we estimate an expected CP-odd difference between the
values of the slope parameters g^+ and g^- of the energy distributions of "odd"
pions in K^+ \to \pi^+\pi^+\pi^- and K^- \to \pi^-\pi^-\pi^+ decays.Comment: 12 pages, no figure
N=1 Matter from Fractional Branes
We study a bound state of fractional D3-branes localized inside the
world-volume of fractional D7-branes on the orbifold C^3/Z_2 x Z_2. We
determine the open string spectrum that leads to N=1 U(N1)xU(N2)xU(N3)xU(N4)
gauge theory with matter having the number of D7-branes as a flavor index. We
derive the linearized boundary action of the D7-brane on this orbifold using
the boundary state formalism and we discuss the tadpole cancellation. After
computing the asymptotic expression of the supergravity solution the anomalies
of the gauge theory are reproduced.Comment: LaTeX 20 pages, 1 figure, small changes and references adde
On the Gauge/Gravity Correspondence and the Open/Closed String Duality
In this article we review the conditions for the validity of the
gauge/gravity correspondence in both supersymmetric and non-supersymmetric
string models. We start by reminding what happens in type IIB theory on the
orbifolds C^2/Z_2 and C^3/(Z_2 x Z_2), where this correspondence beautifully
works. In these cases, by performing a complete stringy calculation of the
interaction among D3 branes, it has been shown that the fact that this
correspondence works is a consequence of the open/closed duality and of the
absence of threshold corrections. Then we review the construction of type 0
theories with their orbifolds and orientifolds having spectra free from both
open and closed string tachyons and for such models we study the validity of
the gauge/gravity correspondence, concluding that this is not a peculiarity of
supersymmetric theories, but it may work also for non-supersymmetric models.
Also in these cases, when it works, it is again a consequence of the
open/closed string duality and of vanishing threshold corrections.Comment: Invited review article for Int. J. Mod. Phys. A, 95 pages, 2 figures,
3 tables, LaTeX. References and acknowledgements adde
The transition in softly broken supersymmetry
We study the effect of supersymmetric contributions to the effective quark
transition , including leading order QCD effects. We apply
the discussion to the decay . Even though one-particle
irreducible contributions could play a role, numerical cancelations make the
amplitude for the two-photon emission strongly correlated to the
amplitude which is sharply constrained by experiment. A quite general statement
follows: as long as non-standard physics effects appear only in the matching of
the Wilson coefficients of the standard effective operator basis, the
deviations from the standard model expectations of the decay rates induced by
are bound to follow closely the corresponding deviations
on . Effects of new physics are therefore bound to be small.Comment: Latex2e, RevTex, 22 pages, 8 eps figures, comments and references
adde
New checks and subtleties for AdS/CFT and a-maximization
We provide a cross-check of AdS/CFT and a-charge maximization for a four
dimensional =1 SCFT with irrational R-charges. The gauge theory is the low
energy effective theory of N D3-branes at the tip of the complex cone over the
first del Pezzo surface. By carefully taking into account the subtle issue of
flavor symmetry breaking at the fixed point, we show, using a-maximization,
that this theory has in fact irrational central charge and R-charges. Our
results perfectly match with those inherited from the recently discovered
supergravity dual background. Along analogous lines, we make novel predictions
for the still unknown AdS dual of the quiver theory for the second del Pezzo
surface. This should flow to a SCFT with irrational charges, too. All of our
results differ from previous findings in the literature and outline interesting
subtleties in a-maximization and AdS/CFT techniques overlooked in the past.Comment: Latex, 16 pagex, 2 figures; v2, comments and a reference added; v3,
typos correcte
Feynman Rules in the Type III Natural Flavour-Conserving Two-Higgs Doublet Model
We consider a two Higgs-doublet model with symmetry, which implies a
rather than 0 relative phase between the vacuum expectation
values . The corresponding Feynman rules are derived
accordingly and the transformation of the Higgs fields from the weak to the
mass eigenstates includes not only an angle rotation but also a phase
transformation. In this model, both doublets couple to the same type of
fermions and the flavour-changing neutral currents are naturally suppressed. We
also demonstrate that the Type III natural flavour-conserving model is valid at
tree-level even when an explicit symmetry breaking perturbation is
introduced to get a reasonable CKM matrix. In the special case , as the ratio runs from 0 to ,
the dominant Yukawa coupling will change from the first two generations to the
third generation. In the Feynman rules, we also find that the charged Higgs
currents are explicitly left-right asymmetric. The ratios between the left- and
right-handed currents for the quarks in the same generations are estimated.Comment: 16 pages (figures not included), NCKU-HEP/93-1
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