10,203 research outputs found
On Symmetry Non-Restoration at High Temperature
We study the effect of next-to-leading order contributions on the phenomenon
of symmetry non-restoration at high temperature in an
model.Comment: 8 pages. Two figures in a separate fil
Reconciling the CAST and PVLAS Results
The PVLAS experiment has recently claimed evidence for an axion-like particle
in the milli-electron-Volt mass range with a coupling to two photons that
appears to be in contradiction with the negative results of the CAST experiment
searching for solar axions. The simple axion interpretation of these two
experimental results is therefore untenable and it has posed a challenge for
theory. We propose a possible way to reconcile these two results by postulating
the existence of an ultralight pseudo-scalar particle interacting with two
photons and a scalar boson and the existence of a low scale phase transition in
the theory.Comment: 4 pages, 2 figures; references update
Can Symmetry non-restoration solve the Monopole Problem?
We reexamine a recently proposed non-inflationary solution to the monopole
problem, based on the possibility that spontaneously broken Grand-Unified
symmetries do not get restored at high temperature. We go beyond leading order
by studying the self-consistent one-loop equations of the model. We find large
next-to-leading corrections that reverse the lowest order results and cause
symmetry restoration at high temperature.Comment: 17 pages plus three coded and compressed postscript files for figure
Higgs Sector of the Minimal Left-Right Symmetric Model
We perform an exhaustive analysis of the most general Higgs sector of the
minimal left-right symmetric model (MLRM). We find that the CP properties of
the vacuum state are connected to the Higgs spectrum: if CP is broken
spontaneously, the MLRM does not approach the Standard Model in the limit of a
decoupling left-right symmetry breaking scale. Depending on the size of the CP
phases scenarios with extra non-decoupling flavor-violating doublet Higgses or
very light SU(2) triplet Higgses emerge, both of which are ruled out by
phenomenology. For zero CP phases the non-standard Higgses decouple only if a
very unnatural fine-tuning condition is fulfilled. We also discuss
generalizations to a non-minimal Higgs sector.Comment: brief discussion of non-minimal Higgs sectors added, journal versio
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
GUTs with dim-5 interactions: Gauge Unification and Intermediate Scales
Dimension-5 corrections to the gauge kinetic term of Grand Unified Theories
(GUTs) may capture effects of quantum gravity or string compactification. Such
operators modify the usual gauge coupling unification prediction in a
calculable manner. Here we examine SU(5), SO(10), and E(6) GUTs in the light of
all such permitted operators and calculate the impact on the intermediate
scales and the unification programme. We show that in many cases at least one
intermediate scale can be lowered to even 1-10 TeV, where a neutral Z' and
possibly other states are expected.Comment: 23 pages, 8 figures, 10 tables, Treatment of U(1) mixing effects
corrected. Published version
Grand Unification in Non-Commutative Geometry
The formalism of non-commutative geometry of A. Connes is used to construct
models in particle physics. The physical space-time is taken to be a product of
a continuous four-manifold by a discrete set of points. The treatment of Connes
is modified in such a way that the basic algebra is defined over the space of
matrices, and the breaking mechanism is planted in the Dirac operator. This
mechanism is then applied to three examples. In the first example the discrete
space consists of two points, and the two algebras are taken respectively to be
those of and matrices. With the Dirac operator
containing the vacuum breaking to , the model is shown
to correspond to the standard model. In the second example the discrete space
has three points, two of the algebras are identical and consist of
complex matrices, and the third algebra consists of functions. With an
appropriate Dirac operator this model is almost identical to the minimal
model of Georgi and Glashow. The third and final example is the
left-right symmetric model Comment: 25 pages, ZU-TH-30/1992 and ETH/TH/92-4
Geometric CP Violation with Extra Dimensions
We discuss how CP symmetry can be broken geometrically through orbifold
projections in hidden extra dimensions in the context of D-brane models for
particle unifications. We present a few toy models to illustrate the idea and
suggest ways to incorporate this technique in the context of realistic models.Comment: 6 pages, one figure; references updated and a new model adde
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