5,657 research outputs found
Brane Decay from the Origin of Time
We present a novel scenario where matter in a spacetime originates from a
decaying brane at the origin of time. The decay could be considered as a ``Big
Bang''-like event at X^0=0. The closed string interpretation is a
time-dependent spacetime with a semi-infinite time direction, with the initial
energy of the brane converted into energy flux from the origin. The open string
interpretation can be viewed as a string theoretic non-singular initial
condition.Comment: 5 pages, 2 eps figure
Open Wilson Lines and Chiral Condensates in Thermal Holographic QCD
We investigate various aspects of a proposal by Aharony and Kutasov
arXiv:0803.3547 [hep-th] for the gravity dual of an open Wilson line in the
Sakai-Sugimoto model or its non-compact version. In particular, we use their
proposal to determine the effect of finite temperature, as well as background
electric and magnetic fields, on the chiral symmetry breaking order parameter.
We also generalize their prescription to more complicated worldsheets and
identify the operators dual to such worldsheets.Comment: 45 pages, 18 figures; added reference
Exoplanet atmospheres with EChO: spectral retrievals using EChOSim
We demonstrate the effectiveness of the Exoplanet Characterisation
Observatory mission concept for constraining the atmospheric properties of hot
and warm gas giants and super Earths. Synthetic primary and secondary transit
spectra for a range of planets are passed through EChOSim (Waldmann & Pascale
2014) to obtain the expected level of noise for different observational
scenarios; these are then used as inputs for the NEMESIS atmospheric retrieval
code and the retrieved atmospheric properties (temperature structure,
composition and cloud properties) compared with the known input values,
following the method of Barstow et al. (2013a). To correctly retrieve the
temperature structure and composition of the atmosphere to within 2 {\sigma},
we find that we require: a single transit or eclipse of a hot Jupiter orbiting
a sun-like (G2) star at 35 pc to constrain the terminator and dayside
atmospheres; 20 transits or eclipses of a warm Jupiter orbiting a similar star;
10 transits/eclipses of a hot Neptune orbiting an M dwarf at 6 pc; and 30
transits or eclipses of a GJ1214b-like planet.Comment: 13 pages, 15 figures, 1 table. Accepted by Experimental Astronomy.
The final publication will shortly be available at Springer via
http://dx.doi.org/10.1007/s10686-014-9397-
Solving Pure Yang Mills in 2+1 Dimensions
We analytically compute the spectrum of the spin zero glueballs in the planar
limit of pure Yang-Mills theory in 2+1 dimensions. The new ingredient is
provided by our computation of a new non-trivial form of the ground state
wave-functional. The mass spectrum of the theory is determined by the zeroes of
Bessel functions, and the agreement with large N lattice data is excellent.Comment: 4 page letter; version to appear in Physical Review Letter
Decomposition of coarse woody debris in a long-term litter manipulation experiment: A focus on nutrient availability
The majority of above-ground carbon in tropical forests is stored in wood, which is returned to the atmosphere during decomposition of coarse woody debris. However, the factors controlling wood decomposition have not been experimentally manipulated over time scales comparable to the length of this process.We hypothesized that wood decomposition is limited by nutrient availability and tested this hypothesis in a long-term litter addition and removal experiment in a lowland tropical forest in Panama. Specifically, we quantified decomposition using a 15-year chronosequence of decaying boles, and measured respiration rates and nutrient limitation of wood decomposer communities.The long-term probability that a dead tree completely decomposed was decreased in plots where litter was removed, but did not differ between litter addition and control treatments. Similarly, respiration rates of wood decomposer communities were greater in control treatments relative to litter removal plots; litter addition treatments did not differ from either of the other treatments. Respiration rates increased in response to nutrient addition (nitrogen, phosphorus, and potassium) in the litter removal and addition treatments, but not in the controls.Established decreases in concentrations of soil nutrients in litter removal plots and increased respiration rates in response to nutrient addition suggest that reduced rates of wood decomposition after litter removal were caused by decreased nutrient availability. The effects of litter manipulations differed directionally from a previous short-term decomposition study in the same plots, and reduced rates of bole decomposition in litter removal plots did not emerge until after more than 6 years of decomposition. These differences suggest that litter-mediated effects on nutrient dynamics have complex interactions with decomposition over time
Fractional S-branes on a Spacetime Orbifold
Unstable D-branes are central objects in string theory, and exist also in
time-dependent backgrounds. In this paper we take first steps to studying brane
decay in spacetime orbifolds. As a concrete model we focus on the R^{1,d}/Z_2
orbifold. We point out that on a spacetime orbifold there exist two kinds of
S-branes, fractional S-branes in addition to the usual ones. We investigate
their construction in the open string and closed string boundary state
approach. As an application of these constructions, we consider a scenario
where an unstable brane nucleates at the origin of time of a spacetime, its
initial energy then converting into energy flux in the form of closed strings.
The dual open string description allows for a well-defined description of this
process even if it originates at a singular origin of the spacetime.Comment: 22 pages, 6 eps figure
On the Glueball Spectrum of Pure Yang-Mills Theory in 2+1 Dimensions
We present details of the analytic computation of the spectrum of lowest spin
glueballs in pure Yang-Mills theory in 2+1 dimensions. The new ingredient is
provided by the conjectured new non-trivial expression for the (quasi)Gaussian
part of the ground state wave-functional. We show that this wave-functional can
be derived by solving the Schrodinger equation under certain assumptions. The
mass spectrum of the theory is determined by the zeros of Bessel functions, and
the agreement with available lattice data is excellent.Comment: 43 pages, 3 figures, LaTeX; version to appear in Physical Review
A Comment on Zero-brane Quantum Mechanics
We consider low energy, non-relativistic scattering of two Dirichlet
zero-branes as an exercise in quantum mechanics. For weak string coupling and
sufficiently small velocity, the dynamics is governed by an effective U(2)
gauge theory in 0+1 dimensions. At low energies, D-brane scattering can
reliably probe distances much shorter than the string scale. The only length
scale in the quantum mechanics problem is the eleven dimensional Planck length.
This provides evidence for the role of scales shorter than the string length in
the weakly coupled dynamics of type IIA strings.Comment: 9 pages, harvmac, improved treatment of 2+1 proble
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