751 research outputs found
The Self-Dual String and Anomalies in the M5-brane
We study the anomalies of a charge self-dual string solution in the
Coulomb branch of M5-branes. Cancellation of these anomalies allows us to
determine the anomaly of the zero-modes on the self-dual string and their
scaling with and . The dimensional reduction of the five-brane
anomalous couplings then lead to certain anomalous couplings for D-branes.Comment: 13 pages, Harvmac, refs adde
Saxion Emission from SN1987A
We study the possibility of emission of the saxion, a superpartner of the
axion, from SN1987A. The fact that the observed neutrino pulse from SN1987A is
in excellent agreement with the current theory of supernovae places a strong
bound on the energy loss into any non-standard model channel, therefore
enabling bounds to be placed on the decay constant, f_a, of a light saxion. The
low-energy coupling of the saxion, which couples at high energies to the QCD
gauge field strength, is expected to be enhanced from QCD scaling, making it
interesting to investigate if the saxion could place stronger bounds on f_a
than the axion itself. Moreover, since the properties of the saxion are
determined by f_a, a constraint on this parameter can be translated into a
constraint on the supersymmetry breaking scale. We find that the bound on f_a
from saxion emission is comparable with the one derived from axion emission due
to a cancellation of leading-order terms in the soft-radiation expansion.Comment: 18 pages, 2 figures; minor changes, typos corrected, version to
appear in JHE
Deconstruction, Lattice Supersymmetry, Anomalies and Branes
We study the realization of anomalous Ward identities in deconstructed
(latticized) supersymmetric theories. In a deconstructed four-dimensional
theory with N=2 supersymmetry, we show that the chiral symmetries only appear
in the infrared and that the anomaly is reproduced in the usual framework of
lattice perturbation theory with Wilson fermions. We then realize the theory on
the world-volume of fractional D-branes on an orbifold. In this brane
realization, we show how deconstructed theory anomalies can be computed via
classical supergravity. Our methods and observations are more generally
applicable to deconstructed/latticized supersymmetric theories in various
dimensions.Comment: 1+27 pages, 2 figures, references adde
Brane World Susy Breaking from String/M Theory
String and M-theory realizations of brane world supersymmetry breaking
scenarios are considered in which visible sector Standard Model fields are
confined on a brane, with hidden sector supersymmetry breaking isolated on a
distant brane. In calculable examples with an internal manifold of any volume
the Kahler potential generically contains brane--brane non-derivative contact
interactions coupling the visible and hidden sectors and is not of the no-scale
sequestered form. This leads to non-universal scalar masses and without
additional assumptions about flavor symmetries may in general induce dangerous
sflavor violation even though the Standard Model and supersymmetry branes are
physically separated. Deviations from the sequestered form are dictated by bulk
supersymmetry and can in most cases be understood as arising from exchange of
bulk supergravity fields between branes or warping of the internal geometry.
Unacceptable visible sector tree-level tachyons arise in many models but may be
avoided in certain classes of compactifications. Anomaly mediated and gaugino
mediated contributions to scalar masses are sub-dominant except in special
circumstances such as a flat or AdS pure five--dimensional bulk geometry
without bulk vector multiplets.Comment: Latex, 83 pages, references adde
Surface Tension between Kaon Condensate and Normal Nuclear Matter Phase
We calculate for the first time the surface tension and curvature coefficient
of a first order phase transition between two possible phases of cold nuclear
matter, a normal nuclear matter phase in equilibrium with a kaon condensed
phase, at densities a few times the saturation density. We find the surface
tension is proportional to the difference in energy density between the two
phases squared. Furthermore, we show the consequences for the geometrical
structures of the mixed phase region in a neutron star.Comment: 7 pages, 5 figures (Latex
Towards the deconstruction of M-theory
We argue that there is an equivalence of M-theory on T^3 \times A_{N-1} with
a four-dimensional non-supersymmetric quiver gauge theory on the Higgs branch.
The quiver theory in question has gauge group SU(N)^{N_4N_6N_8} and is
considered in a strong coupling and large N_{4,6,8} limit. We provide field-
and string-theoretical evidence for the equivalence making use of the
deconstruction technique. In particular, we find wrapped M2-branes in the mass
spectrum of the quiver theory at low energies.Comment: LaTeX, 15 pages, 4 figures, added reference
Strange form factors of the proton: a new analysis of the neutrino (antineutrino) data of the BNL-734 experiment
We consider ratios of elastic neutrino(antineutrino)-proton cross sections
measured by the Brookhaven BNL-734 experiment and use them to obtain the
neutral current (NC) over charged current (CC) neutrino-antineutrino asymmetry.
We discuss the sensitivity of these ratios and of the asymmetry to the
electric, magnetic and axial strange form factors of the nucleon and to the
axial cutoff mass M_A. We show that the effects of the nuclear structure and
interactions on the asymmetry and, in general, on ratios of cross sections are
negligible. We find some restrictions on the possible values of the parameters
characterizing the strange form factors. We show that a precise measurement of
the neutrino-antineutrino asymmetry would allow the extraction of the axial and
vector magnetic strange form factors in a model independent way. The
neutrino-antineutrino asymmetry turns out to be almost independent on the
electric strange form factor and on the axial cutoff mass.Comment: 12 page
Higher Derivative Operators from Scherk-Schwarz Supersymmetry Breaking on T^2/Z_2
In orbifold compactifications on T^2/Z_2 with Scherk-Schwarz supersymmetry
breaking, it is shown that (brane-localised) superpotential interactions and
(bulk) gauge interactions generate at one-loop higher derivative counterterms
to the mass of the brane (or zero-mode of the bulk) scalar field. These
brane-localised operators are generated by integrating out the bulk modes of
the initial theory which, although supersymmetric, is nevertheless
non-renormalisable. It is argued that such operators, of non-perturbative
origin and not protected by non-renormalisation theorems, are generic in
orbifold compactifications and play a crucial role in the UV behaviour of the
two-point Green function of the scalar field self-energy. Their presence in the
action with unknown coefficients prevents one from making predictions about
physics at (momentum) scales close to/above the compactification scale(s). Our
results extend to the case of two dimensional orbifolds, previous findings for
S^1/Z_2 and S^1/(Z_2 x Z_2') compactifications where brane-localised higher
derivative operators are also dynamically generated at loop level, regardless
of the details of the supersymmetry breaking mechanism. We stress the
importance of these operators for the hierarchy and the cosmological constant
problems in compactified theories.Comment: 23 pages, LaTeX, one figure, published version in JHE
Flux Stabilization in 6 Dimensions: D-terms and Loop Corrections
We analyse D-terms induced by gauge theory fluxes in the context of
6-dimensional supergravity models. On the one hand, this is arguably the
simplest concrete setting in which the controversial idea of `D-term uplifts'
can be investigated. On the other hand, it is a very plausible intermediate
step on the way from a 10d string theory model to 4d phenomenology. Our
specific results include the flux-induced one-loop correction to the scalar
potential coming from charged hypermultiplets. Furthermore, we comment on the
interplay of gauge theory fluxes and gaugino condensation in the present
context, demonstrate explicitly how the D-term arises from the gauging of one
of the compactification moduli, and briefly discuss further ingredients that
may be required for the construction of a phenomenologically viable model. In
particular, we show how the 6d dilaton and volume moduli can be simultaneously
stabilized, in the spirit of KKLT, by the combination of an R symmetry twist, a
gaugino condensate, and a flux-induced D-term.Comment: 24 pages, 1 figure v2:minor correction
Nuclear effects in the Drell-Yan process at very high energies
We study Drell-Yan (DY) dilepton production in proton(deuterium)-nucleus and
in nucleus-nucleus collisions within the light-cone color dipole formalism.
This approach is especially suitable for predicting nuclear effects in the DY
cross section for heavy ion collisions, as it provides the impact parameter
dependence of nuclear shadowing and transverse momentum broadening, quantities
that are not available from the standard parton model. For p(D)+A collisions we
calculate nuclear shadowing and investigate nuclear modification of the DY
transverse momentum distribution at RHIC and LHC for kinematics corresponding
to coherence length much longer than the nuclear size. Calculations are
performed separately for transversely and longitudinally polarized DY photons,
and predictions are presented for the dilepton angular distribution.
Furthermore, we calculate nuclear broadening of the mean transverse momentum
squared of DY dileptons as function of the nuclear mass number and energy. We
also predict nuclear effects for the cross section of the DY process in heavy
ion collisions. We found a substantial nuclear shadowing for valence quarks,
stronger than for the sea.Comment: 46 pages, 18 figures, title changed and some discussion added,
accepted for publication in PR
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