6 research outputs found
Higgs Mechanism in Nonlocal Field Theories
We study spontaneous gauge symmetry breaking and the Higgs mechanism in
nonlocal field theories. Motivated by the level truncated action of string
field theory, we consider a class of nonlocal field theories with an
exponential factor of the d'Alembertian attached to the kinetic and mass terms.
Modifications of this kind are known to make mild the UV behavior of loop
diagrams and thus have been studied not only in the context of string theory
but also as an alternative approach to quantum gravity. In this paper we argue
that such a nonlocal theory potentially includes a ghost mode near the nonlocal
scale in the particle spectrum of the symmetry broken phase. This is in sharp
contrast to local field theories and would be an obstruction to making a simple
nonlocal model a UV complete theory. We then discuss a possible way out by
studying nonlocal theories with extra symmetries such as gauge symmetries in
higher spacetime dimensions.Comment: 19 pages, 4 figures; v2: references added, version published in JHE
LHC実験における低スケール弦模型のシグナル
学位の種別:課程博士University of Tokyo(東京大学
Signatures of low-scale string models at the LHC
Low-scale string models, in which the string scale M_s is of the order of TeV
with large extra dimensions, can solve the problems of scale hierarchy and
non-renormalizable quantum gravity in the standard model. String excited states
of the standard model particles are possibly observed as resonances in the
dijet invariant mass distribution at the LHC. There are two properties to
distinguish whether the resonances are due to low-scale string or some other
"new physics". One is a characteristic angular distribution in dijet events at
the resonance due to spin degeneracy of string excited states, and the other is
an appearance of the second resonance at a characteristic mass of second string
excited states. We investigate a possibility to observe these evidences of
low-scale string models by Monte Carlo simulations with a reference value of
M_s = 4 TeV at sqrt{s} = 14 TeV. It is shown that spin degeneracy at the dijet
resonance can be observed by looking the chi-distribution with integrated
luminosity of 20 fb^-1. It is shown that the second resonance can be observed
at rather close to the first resonance in the dijet invariant mass distribution
with integrated luminosity of 50 fb^-1. These are inevitable signatures of
low-scale string models.Comment: 21 pages, 8 figure