430 research outputs found
Matrix String Theory, 2D SYM Instantons and affine Toda systems
Extending a recent result of S.B. Giddings, F. Hacquebord and H. Verlinde, we
show that in the U(N) SYM Matrix theory there exist classical BPS instantons
which interpolate between different closed string configurations via
joining/splitting interactions similar to those of string field theory. We
construct them starting from branched coverings of Riemann surfaces. For the
class of them which we analyze in detail the construction can be made explicit
in terms U(N) affine Toda field theories.Comment: 12 pages, 1 eps figure, JHEP.cls LaTeX2e class file; sign corrected,
ref. and acknowledgements update
Heterotic Matrix String Theory and Riemann Surfaces
We extend the results found for Matrix String Theory to Heterotic Matrix
String Theory, i.e. to a 2d O(N) SYM theory with chiral (anomaly free) matter
and N=(8,0) supersymmetry. We write down the instanton equations for this
theory and solve them explicitly. The solutions are characterized by branched
coverings of the basis cylinder, i.e. by compact Riemann surfaces with
punctures. We show that in the strong coupling limit the action becomes the
heterotic string action plus a free Maxwell action. Moreover the amplitude
based on a Riemann surface with p punctures and h handles is proportional to
g^{2-2h-p}, as expected for the heterotic string interaction theory with string
coupling g_s=1/g.Comment: 17 pages, JHEP LaTeX style, sentence delete
Nucleon-Nucleon Bremsstrahlung emission of massive Axion
We consider the problem of axion production by bremsstrahlung emission in a
nuclear medium. The usual assumption of a massless axion is replaced by more
general hypotheses, so that we can describe the emission process for axions
with mass up to a few MeV. We point out that in certain physical situations the
contribution from non-zero mass is non-negligible. In particular, in the
mechanism for the production of Gamma Ray Bursts via emission of heavy axions
the axion mass m_a ~ 1MeV is comparable with the temperature of the nuclear
medium and thus can not be disregarded. Looking at our results we find, in
fact, a fairly considerable reduction of the axion luminosity in that
mechanism.Comment: 16 pages, 5 figure
Matrix String Theory and its Moduli Space
The correspondence between Matrix String Theory in the strong coupling limit
and IIA superstring theory can be shown by means of the instanton solutions of
the former. We construct the general instanton solutions of Matrix String
Theory which interpolate between given initial and final string configurations.
Each instanton is characterized by a Riemann surface of genus h with n
punctures, which is realized as a plane curve. We study the moduli space of
such plane curves and find out that, at finite N, it is a discretized version
of the moduli space of Riemann surfaces: instead of 3h-3+n its complex
dimensions are 2h-3+n, the remaining h dimensions being discrete. It turns out
that as tends to infinity, these discrete dimensions become continuous, and
one recovers the full moduli space of string interaction theory.Comment: 30 pages, LaTeX, JHEP.cls class file, minor correction
Type II Seesaw at LHC: the Roadmap
In this Letter we revisit the type-II seesaw mechanism based on the addition
of a weak triplet scalar to the standard model. We perform a comprehensive
study of its phenomenology at the LHC energies, complete with the electroweak
precision constraints. We pay special attention to the doubly-charged
component, object of collider searches for a long time, and show how the
experimental bound on its mass depends crucially on the particle spectrum of
the theory. Our study can be used as a roadmap for future complete LHC studies.Comment: 5 pages, 4 figures; added discussion on collider signatures including
the impact on SM Higgs searches and accommodating Higgs to two photon rate,
and references; latest version agrees with the published on
A comparison between standard and crossfeed monopulse radars in presence of rough sea scattering and ship movements
Monopulse radars are widely used in tracking systems, due to their relative
simplicity and theoretical precision, but the presence of multipath
impairs the tracking capabilities of these radars, especially when multipath
signals are strong, as in a naval environment. A special monopulse
setup, the crossfeed, has been proposed in the past to provide an automatic
cancellation from smooth sea multipath. In this contribution,
the performances of such a system are analyzed in presence of rough sea
scattering and compared with those of a standard monopulse setup. Particular
attention is devoted to performance degradations due to possible
phase errors in the passive network implementing the comparator and
due to ship rolling and pitching. This latter requires a full 3D monopulse
simulator for its correct evaluation
String Interactions from Matrix String Theory
The Matrix String Theory, i.e. the two dimensional U(N) SYM with N=(8,8)
supersymmetry, has classical BPS solutions that interpolate between an initial
and a final string configuration via a bordered Riemann surface. The Matrix
String Theory amplitudes around such a classical BPS background, in the strong
Yang--Mills coupling, are therefore candidates to be interpreted in a stringy
way as the transition amplitude between given initial and final string
configurations. In this paper we calculate these amplitudes and show that the
leading contribution is proportional to the factor g_s^{-\chi}, where \chi is
the Euler characteristic of the interpolating Riemann surface and g_s is the
string coupling. This is the factor one expects from perturbative string
interaction theory.Comment: 15 pages, 2 eps figures, JHEP Latex class, misprints correcte
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