222 research outputs found
Probing SO(10) symmetry breaking patterns through sfermion mass relations
We consider supersymmetric SO(10) grand unification where the unified gauge
group can break to the Standard Model gauge group through different chains. The
breaking of SO(10) necessarily involves the reduction of the rank, and
consequent generation of non-universal supersymmetry breaking scalar mass
terms. We derive squark and slepton mass relations, taking into account these
non-universal contributions to the sfermion masses, which can help distinguish
between the different chains through which the SO(10) gauge group breaks to the
Standard Model gauge group. We then study some implications of these
non-universal supersymmetry breaking scalar masses for the low energy
phenomenology.Comment: 13 pages, latex using revtex4, contains 2 figures, replaced with
version accepted for publicatio
Squark and slepton masses as probes of supersymmetric SO(10) unification
We carry out an analysis of the non-universal supersymmetry breaking scalar
masses arising in SO(10) supersymmetric unification. By considering patterns of
squark and slepton masses, we derive a set of sum rules for the sfermion masses
which are independent of the manner in which SO(10) breaks to the Standard
Model gauge group via its SU(5) subgroups. The phenomenology arising from such
non-universality is unaffected by the symmetry breaking pattern, so long as the
breaking occurs via any of the SU(5) subgroups of the SO(10) group.Comment: 15 pages using RevTe
Report of the Supersymmetry Theory Working Group
We provide a mini-guide to some of the possible manifestations of weak scale
supersymmetry. For each of six scenarios we provide a brief description of the
theoretical underpinnings, the adjustable parameters, a qualitative description
of the associated phenomenology at future colliders, comments on how to
simulate each scenario with existing event generators.Comment: Report of Snowmass Supersymmetry Theory Working Group; 14 pages plus
3 figures using latex2e and snow2e.cls; this version has corrected a number
of typos from the first versio
The GUT Scale and Superpartner Masses from Anomaly Mediated Supersymmetry Breaking
We consider models of anomaly-mediated supersymmetry breaking (AMSB) in which
the grand unification (GUT) scale is determined by the vacuum expectation value
of a chiral superfield. If the anomaly-mediated contributions to the potential
are balanced by gravitational-strength interactions, we find a
model-independent prediction for the GUT scale of order . The GUT threshold also affects superpartner masses, and can easily
give rise to realistic predictions if the GUT gauge group is asymptotically
free. We give an explicit example of a model with these features, in which the
doublet-triplet splitting problem is solved. The resulting superpartner
spectrum is very different from that of previously considered AMSB models, with
gaugino masses typically unifying at the GUT scale.Comment: 17 page
Transient Observers and Variable Constants, or Repelling the Invasion of the Boltzmann's Brains
If the universe expands exponentially without end, ``ordinary observers''
like ourselves may be vastly outnumbered by ``Boltzmann's brains,'' transient
observers who briefly flicker into existence as a result of quantum or thermal
fluctuations. One might then wonder why we are so atypical. I show that tiny
changes in physics--for instance, extremely slow variations of fundamental
constants--can drastically change this result, and argue that one should be
wary of conclusions that rely on exact knowledge of the laws of physics in the
very distant future.Comment: 4 pages, LaTeX; v2: added references; v3: more discussion of setting,
alternative approaches, now 5 pages; v4: added discussion of the effect of
quantum fluctuations on varying constants, appendix added, now 7 pages; v5:
new reference, minor correctio
Quintessential Kination and Cold Dark Matter Abundance
The generation of a kination-dominated phase by a quintessential exponential
model is investigated and the parameters of the model are restricted so that a
number of observational constraints (originating from nucleosynthesis, the
present acceleration of the universe and the dark-energy-density parameter) are
satisfied. The decoupling of a thermal cold dark matter particle during the
period of kination is analyzed, the relic density is calculated both
numerically and semi-analytically and the results are compared with each other.
It is argued that the enhancement, with respect to the standard paradigm, of
the cold dark matter abundance can be expressed as a function of the
quintessential density parameter at the onset of nucleosynthesis. We find that
values of the latter quantity close to its upper bound require the
thermal-averaged cross section times the velocity of the cold relic to be
almost three orders of magnitude larger than this needed in the standard
scenario so as compatibility with the cold dark matter constraint is achieved.Comment: Published versio
B(d) --> phi K(S) CP asymmetries as an important probe of supersymmetry
The decay is a special probe of physics beyond the
Standard Model (SM), since it has no SM tree level contribution. Motivated by
recent data suggesting a deviation from the SM for its time-dependent CP
asymmetry, we examine supersymmetric explanations. Chirality preserving
contributions are generically small, unless gluino is relatively light. Higgs
contributions are also too small to explain a large asymmetry. Chirality
flipping and gluino contributions actually can provide sizable
effects without conflict with all related results. We discuss how various
insertions can be distinguished, and argue the needed sizes of mass insertions
are reasonable.Comment: 5 pages, 4 figures. A few typos in the abstract are corrected. This
is a shortened version of hep-ph/021209
Grand-Unification Scale Generation through the Anomalous U(1) Breaking
We discuss the anomalous U(1) gauge symmetry as a mechanism of generating the
grand-unification scale. We conclude that unification to a simple group cannot
be realized unless some parameters are ``tuned'', and that models with product
gauge groups are preferred. We consider the ``R-invariant natural unification''
model with gauge groups SU(5)_{GUT} \times U(3)_H. In this model the
doublet-triplet splitting problem is solved and the unwanted GUT relation m_s =
m_\mu is avoided maintaining m_b = m_\tau. Moreover, R-invariance suppresses
the dangerous proton decays induced by dimension four and five operators.Comment: 14 pages, Latex, references adde
Phenomenology of a realistic accelerating universe using only Planck-scale physics
Modern data is showing increasing evidence that the Universe is accelerating.
So far, all attempts to account for the acceleration have required some
fundamental dimensionless quantities to be extremely small. We show how a class
of scalar field models (which may emerge naturally from superstring theory) can
account for acceleration which starts in the present epoch with all the
potential parameters O(1) in Planck units.Comment: 4 pages including 4 figures. Final version accepted for publication
in PRL with expanded discussion of the relationship to other quintessence
research. No changes to our own wor
Dimensionless supersymmetry breaking couplings, flat directions, and the origin of intermediate mass scales
The effects of supersymmetry breaking are usually parameterized by soft
couplings of positive mass dimensions. However, realistic models also predict
the existence of suppressed, but non-vanishing, dimensionless
supersymmetry-breaking couplings. These couplings are technically hard, but do
not lead to disastrous quadratic divergences in scalar masses, and may be
crucial for understanding low-energy physics. In particular, analytic scalar
quartic couplings that break supersymmetry can lead to intermediate scale
vacuum expectation values along nearly-flat directions. I study the one-loop
effective potential for flat directions in the presence of dimensionless
supersymmetry-breaking terms, and discuss the corresponding renormalization
group equations. I discuss two applications: a minimal model of automatic
R-parity conservation, and an extension of this minimal model which provides a
solution to the \mu problem and an invisible axion.Comment: 28 pages, LaTeX with epsf and axodraw.st
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