135 research outputs found
Supersymmetry breaking induced by radiative corrections
We show that simultaneous gauge and supersymmetry breaking can be induced by
radiative corrections, a la Coleman-Weinberg. When a certain correlation among
the superpotential parameters is present, a local supersymmetry-breaking
minimum is found in the effective potential of a gauge non-singlet field, in a
region where the tree-level potential is almost flat. Supersymmetry breaking is
then transmitted to the MSSM through gauge and chiral messenger loops, thus
avoiding the suppression of gaugino masses characteristic of direct gauge
mediation models. The use of a single field ensures that no dangerous tachyonic
scalar masses are generated at the one-loop level. We illustrate this mechanism
with an explicit example based on an SU(5) model with a single adjoint. An
interesting feature of the scenario is that the GUT scale is increased with
respect to standard unification, thus allowing for a larger colour Higgs
triplet mass, as preferred by the experimental lower bound on the proton
lifetime.Comment: 22 pages, 3 figures. Two references added, small redactional changes,
some discussion improved. Results unchange
Momentum Dependent Vertices , and : The NJL Scalar Hidden by Chiral Symmetry
We calculate the momentum dependence of three particle vertices , and in the context of a
Nambu Jona Lasinio type model. We show how they influence the processes , and and how chiral symmetry
shadows the presence of the .Comment: 9 pages (latex), 5 figures available from the authors, preprint
Coimbra 940506, IJS-TP-94/10, accepted for publication in Zeit. f. Physik
The Boson Loop Background to H -> ZZ at Photon-photon Colliders
We have performed a complete one-loop calculation of in the Standard Model, including both gauge bosons and fermions
in the loop. We confirm the large irreducible continuum background from the
-boson loop found by Jikia. We have included the photon-photon luminosity,
and find that the continuum background of transverse boson pairs prohibits
finding a heavy Higgs with mass \gtap 350 GeV in this decay mode.Comment: 16 pages + 4 PS figures included (uuencoded), MAD/PH/77
Localization of Matter Fields in the 5D Standing Wave Braneworld
We investigate the localization problem of matter fields within the 5D
standing wave braneworld. In this model the brane emits anisotropic waves into
the bulk with different amplitudes along different spatial dimensions. We show
that in the case of increasing warp factor there exist the pure gravitational
localization of all kinds of quantum and classical particles on the brane. For
classical particles the anisotropy of the background metric is hidden, brane
fields exhibit standard Lorentz symmetry in spite of anisotropic nature of the
primordial 5D metric.Comment: The version accepted by JHE
Gravitating global monopoles in extra dimensions and the brane world concept
Multidimensional configurations with Minkowski external space-time and a
spherical global monopole in extra dimensions are discussed in the context of
the brane world concept. The monopole is formed with a hedgehog-like set of
scalar fields \phi^i with a symmetry-breaking potential V depending on the
magnitude \phi^2 = \phi^i \phi^i. All possible kinds of globally regular
configurations are singled out without specifying the shape of V(\phi). These
variants are governed by the maximum value \phi_m of the scalar field,
characterizing the energy scale of symmetry breaking. If \phi_m < \phi_cr
(where \phi_cr is a critical value of \phi related to the multidimensional
Planck scale), the monopole reaches infinite radii while in the ``strong field
regime'', when \phi_m\geq \phi_cr, the monopole may end with a cylinder of
finite radius or possess two regular centers. The warp factors of monopoles
with both infinite and finite radii may either exponentially grow or tend to
finite constant values far from the center. All such configurations are shown
to be able to trap test scalar matter, in striking contrast to RS2 type 5D
models. The monopole structures obtained analytically are also found
numerically for the Mexican hat potential with an additional parameter acting
as a cosmological constant.Comment: 21 pages, 6 figures, latex, gc styl
Localization of Scalar Fluctuations in a Dilatonic Brane-World Scenario
We derive and solve the full set of scalar perturbation equations for a class
of -symmetric five-dimensional geometries generated by a bulk cosmological
constant and by a 3-brane non-minimally coupled to a bulk dilaton field. The
massless scalar modes, like their tensor analogues, are localized on the brane,
and provide long-range four-dimensional dilatonic interactions, which are
generically present even when matter on the brane carries no dilatonic charge.
The shorter-range corrections induced by the continuum of massive scalar modes
are always present: they persist even in the case of a trivial dilaton
background (the standard Randall--Sundrum configuration) and vanishing
dilatonic charges.Comment: 22 pages, late
Limits on scalar leptoquark interactions and consequences for GUTs
A colored weak singlet scalar state with hypercharge 4/3 is one of the
possible candidates for the explanation of the unexpectedly large
forward-backward asymmetry in t tbar production as measured by the CDF and D0
experiments. We investigate the role of this state in a plethora of flavor
changing neutral current processes and precision observables of down-quarks and
charged leptons. Our analysis includes tree- and loop-level mediated
observables in the K and B systems, the charged lepton sector, as well as the Z
to b bbar decay width. We perform a global fit of the relevant scalar
couplings. This approach can explain the (g-2)_mu anomaly while tensions among
the CP violating observables in the quark sector, most notably the nonstandard
CP phase (and width difference) in the Bs system cannot be fully relaxed. The
results are interpreted in a class of grand unified models which allow for a
light colored scalar with a mass below 1TeV. We find that the renormalizable
SU(5) scenario is not compatible with our global fit, while in the SO(10) case
the viability requires the presence of both the 126- and 120-dimensional
representations.Comment: 26 pages, 7 figures; version as publishe
Minimal Supersymmetric Pati-Salam Theory: Determination of Physical Scales
We systematically study the minimal supersymmetric Pati-Salam theory, paying
special attention to the unification constraints. We find that the SU(4)_c
scale M_c and the Left-Right scale M_R lie in the range 10^{10} GeV < M_c <
10^{14} GeV, 10^{3} GeV < M_R <10^{10} GeV (with single-step breaking at
10^{10} GeV), giving a potentially accessible scale of parity breaking. The
theory includes the possibility of having doubly-charged supermultiplets at the
supersymmetry breaking scale; color octet states with mass of order M_R^2/M_c;
magnetic monopoles of intermediate mass that do not conflict with cosmology,
and a 'clean' (type I) form for the see-saw mechanism of neutrino mass.Comment: 5 page
Critical temperature for kaon condensation in color-flavor locked quark matter
We study the behavior of Goldstone bosons in color-flavor-locked (CFL) quark
matter at nonzero temperature. Chiral symmetry breaking in this phase of cold
and dense matter gives rise to pseudo-Goldstone bosons, the lightest of these
being the charged and neutral kaons K^+ and K^0. At zero temperature,
Bose-Einstein condensation of the kaons occurs. Since all fermions are gapped,
this kaon condensed CFL phase can, for energies below the fermionic energy gap,
be described by an effective theory for the bosonic modes. We use this
effective theory to investigate the melting of the condensate: we determine the
temperature-dependent kaon masses self-consistently using the two-particle
irreducible effective action, and we compute the transition temperature for
Bose-Einstein condensation. Our results are important for studies of transport
properties of the kaon condensed CFL phase, such as bulk viscosity.Comment: 24 pages, 8 figures, v2: new section about effect of electric
neutrality on critical temperature added; references added; version to appear
in J.Phys.
Discriminating neutrino mass models using Type II seesaw formula
In this paper we propose a kind of natural selection which can discriminate
the three possible neutrino mass models, namely the degenerate, inverted
hierarchical and normal hierarchical models, using the framework of Type II
seesaw formula. We arrive at a conclusion that the inverted hierarchical model
appears to be most favourable whereas the normal hierarchical model follows
next to it. The degenerate model is found to be most unfavourable. We use the
hypothesis that those neutrino mass models in which Type I seesaw term
dominates over the Type II left-handed Higgs triplet term are favoured to
survive in nature.Comment: No change in the results, a few references added, some changes in
Type[IIB] calculation
- …