1,009 research outputs found
Bulk Fermion Stars with New Dimensions
Many efforts have been devoted to the studies of the phenomenology in
particle physics with extra dimensions. We propose degenerate fermion stars
with extra dimensions and study what features characterized by the size of
extra dimensions should appear in its structure. We find that Kaluza-Klein
excited modes arise for the larger scale of extra dimensions and examine the
conditions on which different layers should be caused in the inside of the
stars. We expound how the extra dimensions affect on physical quantities.Comment: 20 pages, 14 figure
Ultraviolet dependence of Kaluza-Klein effects on electroweak observables
In extensions of the standard model (SM) with d extra dimensions at the TeV
scale the virtual exchange of Kaluza-Klein (KK) excitations of the gauge bosons
gives contributions that change the SM relations between electroweak
observables. These corrections are finite only for d=1; for d\ge 2 the infinite
tower of KK modes gives a divergent contribution that has to be regularized
introducing a cutoff (the string scale). However, the ultraviolet dependence of
the KK effects is completely different if the running of the couplings with the
scale is taken into account. We find that for larger d the number of
excitations at each KK level increases, but their larger number is compensated
by the smaller value of the gauge coupling at that scale. As a result, for any
number of extra dimensions the exchange of the complete KK tower always gives a
finite contribution. We show that (i) for d=1 the running of the gauge coupling
decreases an 14% the effect of the KK modes on electroweak observables; (ii) in
all cases more than 90% of the total effect comes from the excitations in the
seven lowest KK levels and is then independent of ultraviolet physics.Comment: 8 pages, to appear in Phys. Rev.
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
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
Stabilization of Sub-Millimeter Dimensions: The New Guise of the Hierarchy Problem
A new framework for solving the hierarchy problem was recently proposed which
does not rely on low energy supersymmetry or technicolor. The fundamental
Planck mass is at a \tev and the observed weakness of gravity at long
distances is due the existence of new sub-millimeter spatial dimensions. In
this picture the standard model fields are localized to a -dimensional
wall or ``3-brane''. The hierarchy problem becomes isomorphic to the problem of
the largeness of the extra dimensions. This is in turn inextricably linked to
the cosmological constant problem, suggesting the possibility of a common
solution. The radii of the extra dimensions must be prevented from both
expanding to too great a size, and collapsing to the fundamental Planck length
\tev^{-1}. In this paper we propose a number of mechanisms addressing this
question. We argue that a positive bulk cosmological constant can
stabilize the internal manifold against expansion, and that the value of
is not unstable to radiative corrections provided that the
supersymmetries of string theory are broken by dynamics on our 3-brane. We
further argue that the extra dimensions can be stabilized against collapse in a
phenomenologically successful way by either of two methods: 1) Large,
topologically conserved quantum numbers associated with higher-form bulk U(1)
gauge fields, such as the naturally occurring Ramond-Ramond gauge fields, or
the winding number of bulk scalar fields. 2) The brane-lattice-crystallization
of a large number of 3-branes in the bulk. These mechanisms are consistent with
theoretical, laboratory, and cosmological considerations such as the absence of
large time variations in Newton's constant during and after primordial
nucleosynthesis, and millimeter-scale tests of gravity.Comment: Corrected referencing to important earlier work by Sundrum, errors
fixed, additional discussion on radion phenomenology, conclusions unchanged,
23 pages, LaTe
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
Neutrino Masses from Large Extra Dimensions
Recently it was proposed that the standard model (SM) degrees of freedom
reside on a -dimensional wall or ``3-brane'' embedded in a
higher-dimensional spacetime. Furthermore, in this picture it is possible for
the fundamental Planck mass \mst to be as small as the weak scale \mst\simeq
O(\tev) and the observed weakness of gravity at long distances is due the
existence of new sub-millimeter spatial dimensions. We show that in this
picture it is natural to expect neutrino masses to occur in the 10^{-1} -
10^{-4}\ev range, despite the lack of any fundamental scale higher than
\mst. Such suppressed neutrino masses are not the result of a see-saw, but
have intrinsically higher-dimensional explanations. We explore two
possibilities. The first mechanism identifies any massless bulk fermions as
right-handed neutrinos. These give naturally small Dirac masses for the same
reason that gravity is weak at long distances in this framework. The second
mechanism takes advantage of the large {\it infrared} desert: the space in the
extra dimensions. Here, small Majorana neutrino masses are generated by
breaking lepton number on distant branes.Comment: 17 pages, late
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
Ultraviolet sensitivity of rare decays in nonuniversal extra dimensional models
We consider a nonuniversal five dimensional model in which fermions are
localised on a four dimensional brane, while gauge bosons and a scalar doublet
can travel in the bulk. As a result of KK number non-conservation at the
brane-bulk intersection, the ultraviolet divergence does not cancel out in some
physical observables. For example, the decay amplitude is
linearly divergent, while -- mixing amplitude is log divergent. We
attempt to identify the exact source of this nonrenormalizability. We compare
and contrast our results with those obtained in the universal five dimensional
model where all particles travel in the extra dimension.Comment: Latex, 11 pages, uses axodraw.st
Extra Dimensions and Higgs Pair Production at Photon Colliders
We show that new physics effects due to extra dimensions can dramatically
affect Higgs pair production at photon colliders. We find that the cross
section due to extra dimensions with the scale of new physics around 1.5
TeV, the cross section can be as large as 0.11 pb (1.5pb) for monochromatic
photon collision, , with the collider energy TeV for Higgs mass of 100 (350) GeV. The cross section can be 3 fb
(2.7 fb) for the same parameters for collisions using photon beams from
electron or positron back scattered by laser. These cross sections are much
larger than those predicted in the Standard Model. Higgs pair production at
photon colliders can provide useful tests for new physics due to extra
dimensions.Comment: Typos corrected and updated references, Rev-Tex, 11 pages with one
figur
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