4,436 research outputs found
The twisted open string partition function and Yukawa couplings
We use the operator formalism to derive the bosonic contribution to the
twisted open string partition function in toroidal compactifications. This
amplitude describes, for instance, the planar interaction between g+1
magnetized or intersecting D-branes. We write the result both in the closed and
in the open string channel in terms of Prym differentials on the appropriate
Riemann surface. Then we focus on the g=2 case for a 2-torus. By factorizing
the twisted partition function in the open string channel we obtain an explicit
expression for the 3-twist field correlator, which is the main ingredient in
the computation of Yukawa couplings in D-brane phenomenological models. This
provides an alternative method for computing these couplings that does not rely
on the stress-energy tensor technique.Comment: 32 pages, 5 figures, Latex; v2: typos correcte
Brane-Inspired Orientifold Field Theories
In this paper we consider the gauge theory living on the world-volume of a
stack of N D3-branes of Type 0B/\Omega' I_6(-1)^{F_{L}} and of its orbifolds
C^2/Z_2 and C^3/(Z_2 x Z_2). The gauge theories obtained in the three cases are
a brane realization of ``orientifold field theories'' having the bosonic sector
common with N=4,2,1 super Yang-Mills respectively. In these non-supersymmetric
theories, we investigate the possibility of keeping the gauge/gravity
correspondence that has revealed itself so successful in the case of
supersymmetric theories. In the open string framework we compute the
coefficient of the gauge kinetic term showing that the perturbative behaviour
of the orientifold field theory can be obtained from the closed string channel
in the large N limit, where the theory exhibits Bose-Fermi degeneracy.Comment: 27 pages, LaTe
Two-loop Euler-Heisenberg effective actions from charged open strings
We present the multiloop partition function of open bosonic string theory in
the presence of a constant gauge field strength, and discuss its low-energy
limit. The result is written in terms of twisted determinants and differentials
on higher-genus Riemann surfaces, for which we provide an explicit
representation in the Schottky parametrization. In the field theory limit, we
recover from the string formula the two-loop Euler-Heisenberg effective action
for adjoint scalars minimally coupled to the background gauge field.Comment: 32 pages, 3 eps figures, plain LaTeX. References added, minor changes
to the text. Published version, affiliation correcte
Gauge theory renormalizations from the open bosonic string
We present a unified point of view on the different methods available in the
literature to extract gauge theory renormalization constants from the
low-energy limit of string theory. The Bern-Kosower method, based on an
off-shell continuation of string theory amplitudes, and the construction of
low-energy string theory effective actions for gauge particles, can both be
understood in terms of strings interacting with background gauge fields, and
thus reproduce, in the low-energy limit, the field theory results of the
background field method. We present in particular a consistent off-shell
continuation of the one-loop gluon amplitudes in the open bosonic string that
reproduces exactly the results of the background field method in the Feynman
gauge.Comment: 14 pages, latex, no figure
Deep spectroscopy in nearby galaxy clusters: III Orbital structure of galaxies in Abell 85
Galaxies in clusters are strongly affected by their environment. They evolve
according to several physical mechanisms that are active in clusters. Their
efficiency can strongly depend on the orbital configuration of the galaxies.
Our aim is to analyse the orbits of the galaxies in the cluster Abell 85, based
on the study of the galaxy velocity anisotropy parameter. We have solved the
Jeans equation under the assumption that the galaxies in A85 are collisionless
objects, within the spherically symmetric gravitational potential of the
virialized cluster. The mass of the cluster was estimated with X-ray and
caustic analyses. We find that the anisotropy profile of the full galaxy
population in A85 is an increasing monotonic function of the distance from the
cluster centre: on average, galaxies in the central region (r/r200 < 0.3) are
on isotropic orbits, while galaxies in the outer regions are on radial orbits.
We also find that the orbital properties of the galaxies strongly depend on
their stellar colour. In particular, blue galaxies are on less radial orbits
than red galaxies. The different families of cluster galaxies considered here
have the pseudo phase-space density profiles Q(r) and Qr(r) consistent with the
profiles expected in virialized dark matter halos in -body simulations. This
result suggests that the galaxies in A85 have reached dynamical equilibrium
within the cluster potential. Our results indicate that the origin of the blue
and red colour of the different galaxy populations is the different orbital
shape rather than the accretion time.Comment: 15 pages, 15 figures. Accepted for publication at MNRA
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
Three-Loop Results on the Lattice
We present some new three-loop results in lattice gauge theories, for the
Free Energy and for the Topological Susceptibility. These results are an
outcome of a scheme which we are developing (using a symbolic manipulation
language), for the analytic computation of renormalization functions on the
lattice.Comment: (Contribution to Lattice-92 conference). 4 page
Is a classical description of stable non-BPS D-branes possible?
We study the classical geometry produced by a stack of stable (i.e. tachyon
free) non-BPS D-branes present in K3 compactifications of type II string
theory. This classical representation is derived by solving the equations of
motion describing the low-energy dynamics of the supergravity fields which
couple to the non-BPS state. Differently from what expected, this configuration
displays a singular behaviour: the space-time geometry has a repulson-like
singularity. This fact suggests that the simplest setting, namely a set of
coinciding non-interacting D-branes, is not acceptable. We finally discuss the
possible existence of other acceptable configurations corresponding to more
complicated bound states of these non-BPS branes.Comment: Latex file: 41 pages, 5 figures; some minor corrections and
references adde
Implementation of the Duality between Wilson loops and Scattering Amplitudes in QCD
We generalize modern ideas about the duality between Wilson loops and
scattering amplitudes in =4 SYM to large-N (or quenched) QCD. We show
that the area-law behavior of asymptotically large Wilson loops is dual to the
Regge-Veneziano behavior of scattering amplitudes at high energies and fixed
momentum transfer, when quark mass is small and/or the number of particles is
large. We elaborate on this duality for string theory in a flat space,
identifying the asymptotes of the disk amplitude and the Wilson loop of large-N
QCD.Comment: REVTex, 6 pages, 1 figure; v3: refs added; v4pp. to appear in PR
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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