184 research outputs found
New Solution to Doublet-Triplet Splitting Problem in SU(N) SUSY GUTs: Towards an Unification of Flavour
The missing VEV solution to the doublet-triplet splitting problem in general
SU(N) SUSY GUTs is found. Remarkably enough, it requires a strict equality of
numbers of the fundamental colours and flavours in SU(N) and for the even-order
groups (N=2k) gives the predominant breaking channel in the
parameter natural area. The flavour subsymmetry breaking owing to some generic
string inspired extra symmetries of the Higgs superpotential appears not to
affect markedly the basic adjoint vacuum configuration in the model. Thus the
both salient features of SM just as an interplay between colours and flavours
(or families for due assignment of quarks and leptons) so the doublet structure
of the weak interactions could be properly understood and accommodated in the
framework of the minimal SU(8) model. Among its predictions the most crucial
one belongs to the existence on the TeV scale just three families of
pseudo-Goldstone bosons and their superpartners 3(5+\bar 5) + SU(5)-singlets
which noticeably improve the unification picture of MSSM.Comment: 13 pages, LaTe
Black holes and Higgs stability
We study the effect of primordial black holes on the classical rate of
nucleation of AdS regions within the standard electroweak vacuum. We find that
the energy barrier for transitions to the new vacuum, which characterizes the
exponential suppression of the nucleation rate, can be reduced significantly in
the black-hole background. A precise analysis is required in order to determine
whether the the existence of primordial black holes is compatible with the form
of the Higgs potential at high temperature or density in the Standard Model or
its extensions.Comment: 27 pages, 10 figures, conclusions expanded, to appear in JCA
BPS solitons in Lifshitz field theories
Lorentz-invariant scalar field theories in d+1 dimensions with second-order
derivative terms are unable to support static soliton solutions that are both
finite in energy and stable for d>2, a result known as Derrick's theorem.
Lifshitz theories, which introduce higher-order spatial derivatives, need not
obey Derrick's theorem. We construct stable, finite-energy, static soliton
solutions in Lifshitz scalar field theories in 3+1 dimensions with dynamical
critical exponent z=2. We exhibit three generic types: non-topological point
defects, topological point defects, and topological strings. We focus mainly on
Lifshitz theories that are defined through a superpotential and admit BPS
solutions. These kinds of theories are the bosonic sectors of supersymmetric
theories derived from the stochastic dynamics of a scalar field theory in one
higher dimension. If nature obeys a Lifshitz field theory in the ultraviolet,
then the novel topological defects discussed here may exist as relics from the
early universe. Their discovery would prove that standard field theory breaks
down at short distance scales.Comment: 14 pages, 4 figures; v2: references added and the x-axis scale of
each figure has been change
Horava Gravity and Gravitons at a Conformal Point
Recently Horava proposed a renormalizable gravity theory with higher
derivatives by abandoning the Lorenz invariance in UV. Here, I study the Horava
model at , where an anisotropic Weyl symmetry exists in the UV
limit, in addition to the foliation-preserving diffeomorphism. By considering
linear perturbations around Minkowski vacuum, I show that the scalar graviton
mode is completely disappeared and only the usual tensor graviton modes remain
in the physical spectrum. The existence of the UV conformal symmetry is unique
to the theory with the detailed balance and it is quite probable that
be the UV fixed point. This situation is analogous to
, which is Lorentz invariant in the IR limit and is believed to be
the IR fixed point.Comment: Added comments and references, Accepted in GER
Quantum Cosmology Aspects Of D3 Branes and Tachyon Dynamics
We investigate aspects of quantum cosmology in relation to string cosmology
systems that are described in terms of the Dirac-Born-Infeld action. Using the
Silverstein-Tong model, we analyze the Wheeler-DeWitt equation for the rolling
scalar and gravity as well for universe, by obtaining the wave
functions for all dynamical degrees of freedom of the system. We show, that in
some cases one can construct a time dependent version of the Wheeler-DeWitt
(WDW) equation for the moduli field . We also explore in detail the
minisuperspace description of the rolling tachyon when non-minimal gravity
tachyon couplings are inserted into the tachyon action.Comment: 29 pages, 3 figures, REVTeX 4; v2 clarifications, comments and
references added; v3 more typos corrected, additional comments on the
minisuperspace description of unstable universes, version published in JHE
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