6 research outputs found
Invisible Axions and Large-Radius Compactifications
We study some of the novel effects that arise when the QCD axion is placed in
the ``bulk'' of large extra spacetime dimensions. First, we find that the mass
of the axion can become independent of the energy scale associated with the
breaking of the Peccei-Quinn symmetry. This implies that the mass of the axion
can be adjusted independently of its couplings to ordinary matter, thereby
providing a new method of rendering the axion invisible. Second, we discuss the
new phenomenon of laboratory axion oscillations (analogous to neutrino
oscillations), and show that these oscillations cause laboratory axions to
``decohere'' extremely rapidly as a result of Kaluza-Klein mixing. This
decoherence may also be a contributing factor to axion invisibility. Third, we
discuss the role of Kaluza-Klein axions in axion-mediated processes and decays,
and propose several experimental tests of the higher-dimensional nature of the
axion. Finally, we show that under certain circumstances, the presence of an
infinite tower of Kaluza-Klein axion modes can significantly accelerate the
dissipation of the energy associated with cosmological relic axion
oscillations, thereby enabling the Peccei-Quinn symmetry-breaking scale to
exceed the usual four-dimensional relic oscillation bounds. Together, these
ideas therefore provide new ways of obtaining an ``invisible'' axion within the
context of higher-dimensional theories with large-radius compactifications.Comment: 43 pages, LaTeX, 6 figure
A Calculable Toy Model of the Landscape
Motivated by recent discussions of the string-theory landscape, we propose
field-theoretic realizations of models with large numbers of vacua. These
models contain multiple U(1) gauge groups, and can be interpreted as
deconstructed versions of higher-dimensional gauge theory models with fluxes in
the compact space. We find that the vacuum structure of these models is very
rich, defined by parameter-space regions with different classes of stable vacua
separated by boundaries. This allows us to explicitly calculate physical
quantities such as the supersymmetry-breaking scale, the presence or absence of
R-symmetries, and probabilities of stable versus unstable vacua. Furthermore,
we find that this landscape picture evolves with energy, allowing vacua to
undergo phase transitions as they cross the boundaries between different
regions in the landscape. We also demonstrate that supergravity effects are
crucial in order to stabilize most of these vacua, and in order to allow the
possibility of cancelling the cosmological constant.Comment: 49 pages, LaTeX, 13 figures, references adde
Can we predict for the Non-SUSY sector of the Landscape ?
We propose a new selection criteria for predicting the most probable
wavefunction of the universe that propagates on the string landscape
background, by studying its dynamics from a quantum cosmology view. Previously
we applied this proposal to the sector of the landscape. In this work
the dynamic selection criterion is applied to the investigation of the
non- sector.In the absence of detailed information about its structure,
it is assumed that this sector has a stochastic distribution of vacua
energies.The calculation of a distribution probability for the cosmological
constants , obtained from the density of states ,
indicates that the most probable wavefunction is peaked around universes with
zero . In contrast to the {\it extended wavefunction} solutions
found for the sector with -vacua and peaked around
, wavefunctions residing on the non-
sector exhibit {\it Anderson localization}.Although minisuperspace is a limited
approach it presently provides a dynamical quantum selection rule for the most
probable vacua solution from the landscape.Comment: 6 pages, 1 figur
Flavour Physics of Leptons and Dipole Moments.
This chapter of the report of the ``Flavour in the era of the LHC'' Workshop
discusses the theoretical, phenomenological and experimental issues related to
flavour phenomena in the charged lepton sector and in flavour-conserving
CP-violating processes. We review the current experimental limits and the main
theoretical models for the flavour structure of fundamental particles. We
analyze the phenomenological consequences of the available data, setting
constraints on explicit models beyond the Standard Model, presenting benchmarks
for the discovery potential of forthcoming measurements both at the LHC and at
low energy, and exploring options for possible future experiments.Comment: Report of Working Group 3 of the CERN Workshop ``Flavour in the era
of the LHC'', Geneva, Switzerland, November 2005 -- March 200