326 research outputs found
Quantized bulk scalar fields in the Randall-Sundrum brane-model
We examine the lowest order quantum corrections to the effective action
arising from a quantized real scalar field in the Randall-Sundrum background
spacetime. The leading term is the familiar vacuum, or Casimir, energy density.
The next term represents an induced gravity term that can renormalize the
4-dimensional Newtonian gravitational constant. The calculations are performed
for an arbitrary spacetime dimension. Two inequivalent boundary conditions,
corresponding to twisted and untwisted field configurations, are considered. A
careful discussion of the regularization and renormalization of the effective
action is given, with the relevant counterterms found. It is shown that the
requirement of self-consistency of the Randall-Sundrum solution is not simply a
matter of minimizing the Casimir energy density. The massless, conformally
coupled scalar field results are obtained as a special limiting case of our
results. We clarify a number of differences with previous work.Comment: 31 pages, 1 figur
Brane World Cosmological Perturbations
We consider a brane world and its gravitational linear perturbations. We
present a general solution of the perturbations in the bulk and find the
complete perturbed junction conditions for generic brane dynamics. We also
prove that (spin 2) gravitational waves in the great majority of cases can only
arise in connection with a non-vanishing anisotropic stress. This has far
reaching consequences for inflation in the brane world. Moreover, contrary to
the case of the radion, perturbations are stable.Comment: 16 pages, one figur
D-Matter
We study the properties and phenomenology of particle-like states originating
from D-branes whose spatial dimensions are all compactified. They are
non-perturbative states in string theory and we refer to them as D-matter. In
contrast to other non-perturbative objects such as 't Hooft-Polyakov monopoles,
D-matter states could have perturbative couplings among themselves and with
ordinary matter. The lightest D-particle (LDP) could be stable because it is
the lightest state carrying certain (integer or discrete) quantum numbers.
Depending on the string scale, they could be cold dark matter candidates with
properties similar to that of wimps or wimpzillas. The spectrum of excited
states of D-matter exhibits an interesting pattern which could be distinguished
from that of Kaluza-Klein modes, winding states, and string resonances. We
speculate about possible signatures of D-matter from ultra-high energy cosmic
rays and colliders.Comment: 25 pages, 5 figures, references adde
Quantized bulk fermions in the Randall-Sundrum brane model
The lowest order quantum corrections to the effective action arising from
quantized massive fermion fields in the Randall-Sundrum background spacetime
are computed. The boundary conditions and their relation with gauge invariance
are examined in detail. The possibility of Wilson loop symmetry breaking in
brane models is also analysed. The self-consistency requirements, previously
considered in the case of a quantized bulk scalar field, are extended to
include the contribution from massive fermions. It is shown that in this case
it is possible to stabilize the radius of the extra dimensions but it is not
possible to simultaneously solve the hierarchy problem, unless the brane
tensions are dramatically fine tuned, supporting previous claims.Comment: 25 pages, 1 figure, RevTe
Brane Cosmology in the Background of D-Brane with NS B Field
We study the cosmological evolution of the four-dimensional universe on the
probe D3-brane in geodesic motion in the curved background of the source
Dp-brane with non-zero NS B field. The Friedman equations describing the
expansion of the brane universe are obtained and analyzed for various limits.
We elaborate on corrections to the cosmological evolution due to nonzero NS B
field.Comment: 13 pages, LaTeX, revised version with minor corrections to appear in
Phys. Rev.
Models of Dynamical Supersymmetry Breaking with Gauged Symmetry
We present simple models of dynamical supersymmetry breaking with gauged
U(1)_R symmetry. The minimal supersymmetric standard model and supersymmetric
SU(5) GUT are considered as the visible sector. The anomaly cancellation
conditions for U(1)_R are investigated in detail and simple solutions of the
R-charge assignments are found. We show that this scenario of dynamical
supersymmetry breaking is phenomenologically viable with the gravitino mass of
order 1 TeV or 10 TeV.Comment: 15 pages, uses REVTEX macro, No figure
R-mediation of Dynamical Supersymmetry Breaking
We propose a simple scenario of the dynamical supersymmetry breaking in four
dimensional supergravity theories. The supersymmetry breaking sector is assumed
to be completely separated as a sequestered sector from the visible sector,
except for the communication by the gravity and U(1)_R gauge interactions, and
the supersymmetry breaking is mediated by the superconformal anomaly and U(1)_R
gauge interaction. Supersymmetry is dynamically broken by the interplay between
the non-perturbative effect of the gauge interaction and Fayet-Iliopoulos
D-term of U(1)_R which necessarily exists in supergravity theories with gauged
U(1)_R symmetry. We construct an explicit model which gives phenomenologically
acceptable mass spectrum of superpartners with vanishing (or very small)
cosmological constant.Comment: 12 pages, to be published in Phys. Rev.
Stress-energy tensor for a quantised bulk scalar field in the Randall-Sundrum brane model
We calculate the vacuum expectation value of the stress-energy tensor for a
quantised bulk scalar field in the Randall-Sundrum model, and discuss the
consequences of its local behaviour for the self-consistency of the model. We
find that, in general, the stress-energy tensor diverges in the vicinity of the
branes. Our main conclusion is that the stress-energy tensor is sufficiently
complicated that it has implications for the effective potential, or radion
stabilisation, methods that have so far been used.Comment: 16 pages, 3 figures. Minor changes made and references added. To
appear in Phys. Rev.
Variable-Speed-of-Light Cosmology from Brane World Scenario
We argue that the four-dimensional universe on the TeV brane of the
Randall-Sundrum scenario takes the bimetric structure of Clayton and Moffat,
with gravitons traveling faster than photons instead, while the radion varies
with time. We show that such brane world bimetric model can thereby solve the
flatness and the cosmological constant problems, provided the speed of a
graviton decreases to the present day value rapidly enough. The resolution of
other cosmological problems such as the horizon problem and the monopole
problem requires supplementation by inflation, which may be achieved by the
radion field provided the radion potential satisfies the slow-roll
approximation.Comment: 18 pages, LaTeX, revised version to appear in Phys. Rev.
Calcium channels controlling acetylcholine release from preganglionic nerve terminals in rat autonomic ganglia
Little is known about the nature of the calcium channels controlling neurotransmitter release from preganglionic parasympathetic nerve fibres. In the present study, the effects of selective calcium channel antagonists and amiloride were investigated on ganglionic neurotransmission. Conventional intracellular recording and focal extracellular recording techniques were used in rat submandibular and pelvic ganglia, respectively. Excitatory postsynaptic potentials and excitatory postsynaptic currents preceded by nerve terminal impulses were recorded as a measure of acetylcholine release from parasympathetic and sympathetic preganglionic fibres following nerve stimulation. The calcium channel antagonists omega-conotoxin GVIA (N type), nifedipine and nimodipine (L type), omega-conotoxin MVIIC and omega-agatoxin IVA (P/Q type), and Ni2+ (R type) had no functional inhibitory effects on synaptic transmission in both submandibular and pelvic ganglia. The potassium-sparing diuretic, amiloride, and its analogue, dimethyl amiloride, produced a reversible and concentration-dependent inhibition of excitatory postsynaptic potential amplitude in the rat submandibular ganglion. The amplitude and frequency of spontaneous excitatory postsynaptic potentials and the sensitivity of the postsynaptic membrane to acetylcholine were unaffected by amiloride. In the rat pelvic ganglion, amiloride produced a concentration-dependent inhibition of excitatory postsynaptic currents without causing any detectable effects on the amplitude or configuration of the nerve terminal impulse. These results indicate that neurotransmitter release from preganglionic parasympathetic and sympathetic nerve terminals is resistant to inhibition by specific calcium channel antagonists of N-, L-, P/Q- and R-type calcium channels. Amiloride acts presynaptically to inhibit evoked transmitter release, but does not prevent action potential propagation in the nerve terminals, suggesting that amiloride may block the pharmacologically distinct calcium channel type(s) on rat preganglionic nerve terminals. (C) 1999 IBRO. Published by Elsevier Science Ltd
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