195 research outputs found
Bulk fields in the Randall-Sundrum compactification scenario
Recently, Randall and Sundrum proposed a solution to the hierarchy problem where the background spacetime is five dimensional. There are two 3-branes, and the mass scale for fields that propagate on one of the 3-branes is exponentially suppressed relative to the fundamental scale of the theory, which is taken to be the Planck mass MPl. In this Brief Report we show that bulk fields with a five dimensional mass term of order MPl have, after integrating over the extra dimension, modes with four-dimensional masses that are exponentially suppressed as well. This opens the possibility that in this scenario the standard model matter fields may correspond to degrees of freedom that are not confined to a 3-brane
Modulus Stabilization with Bulk Fields
We propose a mechanism for stabilizing the size of the extra dimension in the
Randall-Sundrum scenario. The potential for the modulus field that sets the
size of the fifth dimension is generated by a bulk scalar with quartic
interactions localized on the two 3-branes. The minimum of this potential
yields a compactification scale that solves the hierarchy problem without fine
tuning of parameters.Comment: 8 pages, LaTeX; minor typo correcte
The Long Range Gravitational Potential Energy Between Strings
We calculate the gravitational potential energy between infinitely long
parallel strings with tensions \tau_1 and \tau_2. Classically, it vanishes, but
at one loop, we find that the long range gravitational potential energy per
unit length is U/L = 24G_N^2\tau_1\tau_2/(5 \pi a^2) + ..., where a is the
separation between the strings, G_N is Newton's constant, and we set \hbar = c
=1. The ellipses represent terms suppressed by more powers of G_N \tau_i.
Typically, massless bulk fields give rise at one loop to a long range potential
between p-branes in space-times of dimension p+2+1. The contribution to this
potential from bulk scalars is computed for arbitrary p (strings correspond to
p=1) and in the case of three-branes its possible relevance for cosmological
quintessence is commented on.Comment: 10 pages, 6 figure
Toward a unified description of hadro- and photoproduction: S-wave pi- and eta-photoproduction amplitudes
The Chew-Mandelstam parameterization, which has been used extensively in the
two-body hadronic sector, is generalized in this exploratory study to the
electromagnetic sector by simultaneous fits to the pion- and
eta-photoproduction S-wave multipole amplitudes for center-of-mass energies
from the pion threshold through 1.61 GeV. We review the Chew-Mandelstam
parameterization in detail to clarify the theoretical content of the SAID
hadronic amplitude analysis and to place the proposed, generalized SAID
electromagnetic amplitudes in the context of earlier employed parameterized
forms. The parameterization is unitary at the two-body level, employing four
hadronic channels and the gamma-N electromagnetic channel. We compare the
resulting fit to the MAID parameterization and find qualitative agreement
though, numerically, the solution is somewhat different. Applications of the
extended parameterization to global fits of the photoproduction data and to
global fits of the combined hadronic and photoproduction data are discussed.Comment: 9 pages, 9 figures; added figures and tex
Prevalence of drug and alcohol use in urban Afghan istan: epidemiological data from the Afghanistan National Urban Drug Use Study (ANUDUS)
Background Previous attempts to assess the prevalence of drug use in Afghanistan have focused on subgroups that
are not generalisable. In the Afghanistan National Urban Drug Use Study, we assessed risk factors and drug use in
Afghanistan through self-report questionnaires that we validated with laboratory test confi rmation using analysis of
hair, urine, and saliva.
Methods The study took place between July 13, 2010, to April 25, 2012, in 11 Afghan provinces . 2187 randomly selected
households completed a survey, representing 19 025 ho usehold members. We completed surveys with the female
head of the household about past and current drug use among members of their household . We also obtained hair,
urine, and saliva samples from 5236 people in these households and tested them for metabolites of 13 drugs.
Find ings Of 2170 households with biological samples tested, 247 (11·4%) tested positive for any drug. Overall, opioids
were the most prevale nt drug in the biological samples (5·6%), although prescription drugs (prescription pain pills,
sedatives, and tranquilliser) were the most commonly reported in the past 30 days in the questionnaires (7·6%). Of
individuals testing positive for at least one substance, opioids accounted for more than 50% of substance use in
women and children, but only a third of substances in men, who predominantly tested positive for cannabinoids.
After controlling for age with direct standardisation, individual prevalence of substance use (from laboratory tests)
was 7·2% (95% CI 6·1–8·3) in men and 3·1% (2·5–3·7) in women—with a national prevalence of 5·1% (4·4–5·8)
and a prevalence of 5·0% (4·1–5·8) in Kabul. Concordance between laboratory test results and self-reports was high.
Interpretation These data suggest the female head of household to be a knowledgeable informant for household
substance use. They also might provide insight into new avenues for targeted behavioural interventions and
prevention messages
Exercise based assessment of cardiac autonomic function in type 1 versus type 2 diabetes mellitus
Background: Cardiac autonomic neuropathy (CAN) is a complication of diabetes mellitus (DM) that is associated with increased mortality. Exercise-based assessment of autonomic function has identified diminished parasympathetic reactivation after exercise in type 2 DM. It is postulated herein, that this would be more prominent among those with type 1 DM.
Methods: Sixteen subjects with type 1 DM (age 32.9 ± 10.1 years), 18 subjects with type 2 DM (55.4 ± 8.0 years) and 30 controls (44.0 ± 11.6 years) underwent exercise-based assessment of autonomic function. Two 16-min submaximal bicycle tests were performed followed by 45 min of recovery. On the 2nd test, atropine (0.04 mg/kg) was administered near end-exercise so that all of the recovery occurred under parasympathetic blockade. Plasma epinephrine and norepinephrine levels were measured at rest, during exercise, and during recovery.
Results: There were no differences in resting or end-exercise heart rates in the three groups. Parasympathetic effect on RR-intervals during recovery (p < 0.03) and heart rate recovery (p = 0.02) were blunted in type 2 DM. Type 1 DM had higher baseline epinephrine and norepinephrine levels (p < 0.03), and exhibited persistent sympathoexcitation during recovery.
Conclusions: Despite a longer duration of DM in the study patients with type 1 versus type 2 DM, diminished parasympathetic reactivation was not noted in type 1 DM. Instead, elevation in resting plasma catecholamines was noted compared to type 2 DM and controls. The variable pathophysiology for exercise-induced autonomic abnormalities in type 1 versus type 2 DM may impact prognosis
Nucleon-Nucleon Scattering from Effective Field Theory
We perform a nonperturbative calculation of the 1S0 NN scattering amplitude
using an effective field theory (EFT) expansion. The expansion we advocate is a
modification of what has been used previously; it is no a chiral expansion in
powers of the pion mass. We use dimensional regularization throughout and the
MS-bar subtraction scheme; our final result depends only on physical
observables. We show that the EFT expansion of the quantity |p|cot delta(p)
converges at momenta much greater than the scale that characterizes the
derivative expansion of the EFT Lagrangian. Our conclusions are optimistic
about the applicability of an EFT approach to the quantitative study of nuclear
matter.Comment: Revised discussion of power counting in the EFT expansion. Tex file
uses harvmac, epsf macros, 35 pages with 9 postscript figure
Renormalization Group Flows for Brane Couplings
Field theories in the presence of branes encounter localized divergences that
renormalize brane couplings. The sources of these brane-localized divergences
are understood as arising either from broken translation invariance, or from
short distance singularities as the brane thickness vanishes. While the former
are generated only by quantum corrections, the latter can appear even at the
classical level. Using as an example six-dimensional scalar field theory in the
background of a 3-brane, we show how to interpret such classical divergences by
the usual regularization and renormalization procedure of quantum field theory.
In our example, the zero thickness divergences are logarithmic, and lead
classically to non-trivial renormalization group flows for the brane couplings.
We construct the tree level renormalization group equations for these couplings
as well as the one-loop corrections to these flows from bulk-to-brane
renormalization effects.Comment: 16 pages, LaTeX. References and an appendix adde
Classical Stabilization of Homogeneous Extra Dimensions
If spacetime possesses extra dimensions of size and curvature radii much
larger than the Planck or string scales, the dynamics of these extra dimensions
should be governed by classical general relativity. We argue that in general
relativity, it is highly nontrivial to obtain solutions where the extra
dimensions are static and are dynamically stable to small perturbations. We
also illustrate that intuition on equilibrium and stability built up from
non-gravitational physics can be highly misleading. For all static, homogeneous
solutions satisfying the null energy condition, we show that the Ricci
curvature of space must be nonnegative in all directions. Much of our analysis
focuses on a class of spacetime models where space consists of a product of
homogeneous and isotropic geometries. A dimensional reduction of these models
is performed, and their stability to perturbations that preserve the spatial
symmetries is analyzed. We conclude that the only physically realistic examples
of classically stabilized large extra dimensions are those in which the
extra-dimensional manifold is positively curved.Comment: 25 pages; minor changes, improved reference
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