1,434 research outputs found
On Effective Theory of Brane World with Small Tension
The five dimensional theory compactified on with two ``branes'' (two
domain walls) embedded in it is constructed, based on the field-theoretic
mechanism to generate the ``brane''. Some light states localized in the
``brane'' appear in the theory. One is the Nambu-Goldstone boson, which
corresponds to the breaking of the translational invariance in the transverse
direction of the ``brane''. In addition, if the tension of the ``brane'' is
smaller than the fundamental scale of the original theory, it is found that
there may exist not only massless states but also some massive states lighter
than the fundamental scale in the ``brane''. We analyze the four dimensional
effective theory by integrating out the freedom of the fifth dimension. We show
that some effective couplings can be explicitly calculated. As one of our
results, some effective couplings of the state localized in the ``brane'' to
the higher Kaluza-Klein modes in the bulk are found to be suppressed by the
width of the ``brane''. The resultant suppression factor can be quantitatively
different from the one analyzed by Bando et al. using the Nambu-Goto action,
while they are qualitatively the same.Comment: 17 pages, uses REVTEX macr
Higher dimensional models of light Majorana neutrinos confronted by data
We discuss experimental and observational constraints on certain models of
higher dimensional light Majorana neutrinos. Models with flavor blind
brane-bulk couplings plus three or four flavor diagonal light Majorana
neutrinos on the brane, with subsequent mixing induced solely by the
Kaluza-Klein tower of states, are found to be excluded by data on the
oscillations of solar, atmospheric and reactor neutrinos, taken together with
the WMAP upper bound on the sum of neutrino masses. Extra dimensions, if
relevant to neutrino mixing, need to discriminate between neutrino flavors.Comment: 5 pages, Revtex4, 2 PS figures. Fig. 2a and 2b from earlier version
are now combined into one figure. Minor modifications in the text. References
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Infrared alignment of SUSY flavor structures
The various experimental bounds on flavor-changing interactions severely
restrict the low-energy flavor structures of soft supersymmetry breaking
parameters. In this work, we show that with a particular assumption of Yukawa
couplings, the fermion mass and sfermion soft mass matrices are simultaneously
diagonalized by common mixing matrices and we then obtain an alignment solution
for the flavor problems. The required condition is generated by renormalization
group evolutions and achieved at low-energy scale independently of high-energy
structures of couplings. In this case, the diagonal entries of the soft scalar
mass matrices are determined by gaugino and Higgs soft masses. We also discuss
possible realizations of this scenario and the characteristic sparticle
spectrum in the models.Comment: 18 pages, 1 figur
Searching for bosons decaying to gluons
The production and decay of a new heavy vector boson, a chromophilic
vector boson, is described. The chromophilic couples only to two gluons,
but its two-body decays are absent, leading to a dominant decay mode of
. The unusual nature of the interaction predicts a
cross-section which grows with for a fixed coupling and an
accompanying gluon with a coupling that rises with its energy. We study the
decay mode, proposing distinct reconstruction techniques for the
observation of an excess and for the measurement of . We estimate the
sensitivity of current experimental datasets.Comment: For submission to PR
Search for solar Kaluza-Klein axions in theories of low-scale quantum gravity
We explore the physics potential of a terrestrial detector for observing
axionic Kaluza-Klein excitations coming from the Sun within the context of
higher-dimensional theories of low-scale quantum gravity. In these theories,
the heavier Kaluza-Klein axions are relatively short-lived and may be detected
by a coincidental triggering of their two-photon decay mode. Because of the
expected high multiplicity of the solar axionic excitations, we find
experimental sensitivity to a fundamental Peccei-Quinn axion mass up to
eV (corresponding to an effective axion-photon coupling GeV) in theories with 2 extra
dimensions and a fundamental quantum-gravity scale of order 100
TeV, and up to eV (corresponding to GeV) in theories with 3 extra dimensions and
TeV. For comparison, based on recent data obtained from lowest
level underground experiments, we derive the experimental limits: GeV and GeV in the
aforementioned theories with 2 and 3 large compact dimensions, respectively.Comment: 19 pages, extended version, as to appear in Physical Review
Compact Hyperbolic Extra Dimensions: Branes, Kaluza-Klein Modes and Cosmology
We reconsider theories with low gravitational (or string) scale M_* where
Newton's constant is generated via new large-volume spatial dimensions, while
Standard Model states are localized to a 3-brane. Utilizing compact hyperbolic
manifolds (CHM's) we show that the spectrum of Kaluza-Klein (KK) modes is
radically altered. This allows an early universe cosmology with normal
evolution up to substantial temperatures, and completely negates the
constraints on M_* arising from astrophysics. Furthermore, an exponential
hierarchy between the usual Planck scale and the true fundamental scale of
physics can emerge with only order unity coefficients. The linear size of the
internal space remains small. The proposal has striking testable signatures.Comment: 4 pages, no figure
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
Phenomenology of the 1/N Expansion for Field Theories in Extra Dimensions
In this paper we review the properties of the 1/ expansion in
multidimensional theories. Contrary to the usual perturbative expansion it is
renormalizable and contains only logarithmic divergencies. The price for it is
the presence of ghost states which, however, in certain cases do not contribute
to physical amplitudes. In this case the theory is unitary and one can
calculate the cross-sections. As an example we consider the differential cross
section of elastic scattering in -dimensional world. We
look also for the unification of the gauge couplings in multidimensional
Standard Model and its SUSY extension which takes place at energies lower than
in 4 dimensions.Comment: Submitted for the SUSY07 proceedings, 4 pages, LaTeX, 4 eps figures +
3 axodraw figure
Indirect Collider Signals for Extra Dimensions
A recent suggestion that quantum gravity may become strong near the weak
scale has several testable consequences. In addition to probing for the new
large (submillimeter) extra dimensions associated with these theories via
gravitational experiments, one could search for the Kaluza Klein towers of
massive gravitons which are predicted in these models and which can interact
with the fields of the Standard Model. Here we examine the indirect effects of
these massive gravitons being exchanged in fermion pair production in \epem
annihilation and Drell-Yan production at hadron colliders. In the latter case,
we examine a novel feature of this theory, which is the contribution of gluon
gluon initiated processes to lepton pair production. We find that these
processes provide strong bounds, up to several TeV, on the string scale which
are essentially independent of the number of extra dimensions. In addition, we
analyze the angular distributions for fermion pair production with spin-2
graviton exchanges and demonstrate that they provide a smoking gun signal for
low-scale quantum gravity which cannot be mimicked by other new physics
scenarios.Comment: Corrected typos, added table and reference
Fermion masses and quantum numbers from extra dimensions
We study the localization of fermions on a brane embedded in a space-time
with geometry. Quantum numbers of localized fermions are
associated with their rotation momenta around the brane. Fermions with
different quantum numbers have different higher-dimensional profiles. Fermion
masses and mixings, which are proportional to the overlap of higher-dimensional
profiles of the fermions, depend on the fermion quantum numbers.Comment: 14 page
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