5,507 research outputs found
R-Parity Violation and Unification
The reported anomaly in deep-inelastic scattering at HERA has revived
interest in the phenomenology of R-parity violation. From the theoretical point
of view, the existence of R-violating interactions poses two considerable
problems. The first one concerns the flavour structure of the interactions and
the origin of an appropriate suppression of flavour-changing neutral-current
processes and lepton-family transitions. The second one concerns the way of
embedding R-violating interactions in a grand unified theory (GUT) without
introducing unacceptable nucleon decay rates. We show that the second problem
can be solved by a mechanism which is purely group theoretical and does not
rely on details of the flavour theory. We construct explicit GUT models in
which our mechanism can be realized.Comment: Flipped SU(5) example modified. Conclusions unchange
Statistics on the Heterotic Landscape: Gauge Groups and Cosmological Constants of Four-Dimensional Heterotic Strings
Recent developments in string theory have reinforced the notion that the
space of stable supersymmetric and non-supersymmetric string vacua fills out a
``landscape'' whose features are largely unknown. It is then hoped that
progress in extracting phenomenological predictions from string theory -- such
as correlations between gauge groups, matter representations, potential values
of the cosmological constant, and so forth -- can be achieved through
statistical studies of these vacua. To date, most of the efforts in these
directions have focused on Type I vacua. In this note, we present the first
results of a statistical study of the heterotic landscape, focusing on more
than 10^5 explicit non-supersymmetric tachyon-free heterotic string vacua and
their associated gauge groups and one-loop cosmological constants. Although
this study has several important limitations, we find a number of intriguing
features which may be relevant for the heterotic landscape as a whole. These
features include different probabilities and correlations for different
possible gauge groups as functions of the number of orbifold twists. We also
find a vast degeneracy amongst non-supersymmetric string models, leading to a
severe reduction in the number of realizable values of the cosmological
constant as compared with naive expectations. Finally, we also find strong
correlations between cosmological constants and gauge groups which suggest that
heterotic string models with extremely small cosmological constants are
overwhelmingly more likely to exhibit the Standard-Model gauge group at the
string scale than any of its grand-unified extensions. In all cases, heterotic
worldsheet symmetries such as modular invariance provide important constraints
that do not appear in corresponding studies of Type I vacua.Comment: 58 pages, LaTeX, 17 figures, 3 tables; v2: one new figure and
references adde
The Strongly-Interacting Light Higgs
We develop a simple description of models where electroweak symmetry breaking
is triggered by a light composite Higgs, which emerges from a
strongly-interacting sector as a pseudo-Goldstone boson. Two parameters broadly
characterize these models: m_rho, the mass scale of the new resonances and
g_rho, their coupling. An effective low-energy Lagrangian approach proves to be
useful for LHC and ILC phenomenology below the scale m_rho. We identify two
classes of operators: those that are genuinely sensitive to the new strong
force and those that are sensitive to the spectrum of the resonances only.
Phenomenological prospects for the LHC and the ILC include the study of
high-energy longitudinal vector boson scattering, strong double-Higgs
production and anomalous Higgs couplings. We finally discuss the possibility
that the top quark could also be a composite object of the strong sector.Comment: 45 pages, 1 figure. v2: references adde
Unificaxion
Dark matter, gauge coupling unification, and the strong CP problem find a
common and simple solution (in the absence of naturalness) within axion models.
We show that such solution, even without specifying the details of the model
implementation, makes testable predictions for the experimentally measurable
axion parameters: the axion mass and its coupling to photons.Comment: 16 pages, 5 figure
Smallness of Baryon Asymmetry from Split Supersymmetry
The smallness of the baryon asymmetry in our universe is one of the greatest
mysteries and may originate from some profound physics beyond the standard
model. We investigate the Affleck-Dine baryogenesis in split supersymmetry, and
find that the smallness of the baryon asymmetry is directly related to the
hierarchy between the supersymmetry breaking squark/slepton masses and the weak
scale. Put simply, the baryon asymmetry is small because of the split mass
spectrum.Comment: 4 pages, no figur
PeV-Scale Supersymmetry
Although supersymmetry has not been seen directly by experiment, there are
powerful physics reasons to suspect that it should be an ingredient of nature
and that superpartner masses should be somewhat near the weak scale. I present
an argument that if we dismiss our ordinary intuition of finetuning, and focus
entirely on more concrete physics issues, the PeV scale might be the best place
for supersymmetry. PeV-scale supersymmetry admits gauge coupling unification,
predicts a Higgs mass between 125 GeV and 155 GeV, and generally disallows
flavor changing neutral currents and CP violating effects in conflict with
current experiment. The PeV scale is motivated independently by dark matter and
neutrino mass considerations.Comment: 5 RevTex page
Supersymmetry-Breaking Loops from Analytic Continuation into Superspace
We extend to all orders in perturbation theory a method to calculate
supersymmetry-breaking effects by analytic continuation of the renormalization
group into superspace. A central observation is that the renormalized gauge
coupling can be extended to a real vector superfield, thereby including soft
breaking effects in the gauge sector. We explain the relation between this
vector superfield coupling and the "holomorphic" gauge coupling, which is a
chiral superfield running only at 1 loop. We consider these issues for a number
of regulators, including dimensional reduction. With this method, the
renormalization group equations for soft supersymmetry breaking terms are
directly related to supersymmetric beta functions and anomalous dimensions to
all orders in perturbation theory. However, the real power of the formalism
lies in computing finite soft breaking effects corresponding to high-loop
component calculations. We prove that the gaugino mass in gauge-mediated
supersymmetry breaking is ``screened'' from strong interactions in the
messenger sector. We present the complete next-to-leading calculation of
gaugino masses (2 loops) and sfermion masses (3 loops) in minimal gauge
mediation, and several other calculations of phenomenological relevance.Comment: 50 pages, 1 ps and 1 eps figure, LaTe
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Behaviour change at work: Empowering energy efficiency in the workplace through user-centred design
Copyright @ 2011 University of California eScholarship RepositoryCO2 emissions from non-domestic buildings - primarily workplaces - make up 18 percent of the UK's carbon footprint. A combination of technology advances and behavioural changes have the potential to make significant impact, but interventions have often been planned in ways which do not take into account the needs, levels of understanding and everyday behavioural contexts of building users - and hence do not achieve the hoped-for success.This paper provides a brief introduction to the Empower project, a current industrial-academic collaboration in the UK which is applying methods from user-centred design practice to understand diverse users' needs, priorities, mental models of energy and decision-making heuristics - as well as the affordances available to them - in a number of office buildings. We are developing and trialling a set of low-cost, simple software interventions tailored to multiple user groups with different degrees of agency over their energy use, which seek to influence more energy efficient behaviour at work in areas such as HVAC, lighting and equipment use. The project comprises an ethnographic research phase, a participatory design programme involving building users in the design of interventions, and iterative trials in a large office building in central London
Stabilization of the Electroweak Vacuum by a Scalar Threshold Effect
We show how a heavy scalar singlet with a large vacuum expectation value can
evade the potential instability of the Standard Model electroweak vacuum. The
quartic interaction between the heavy scalar singlet and the Higgs doublet
leads to a positive tree-level threshold correction for the Higgs quartic
coupling, which is very effective in stabilizing the potential. We provide
examples, such as the see-saw, invisible axion and unitarized Higgs inflation,
where the proposed mechanism is automatically implemented in well-defined
ranges of Higgs masses.Comment: 18 pages, 5 figure
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