351 research outputs found
Complete Order alpha_s^3 Results for e^+ e^- to (gamma,Z) to Four Jets
We present the next-to-leading order (O(alpha_s^3)) perturbative QCD
predictions for e^+e^- annihilation into four jets. A previous calculation
omitted the O(alpha_s^3) terms suppressed by one or more powers of 1/N_c^2,
where N_c is the number of colors, and the `light-by-glue scattering'
contributions. We find that all such terms are uniformly small, constituting
less than 10% of the correction. For the Durham clustering algorithm, the
leading and next-to-leading logarithms in the limit of small jet resolution
parameter y_{cut} can be resummed. We match the resummed results to our
fixed-order calculation in order to improve the small y_{cut} prediction.Comment: Latex2e, 17 pages with 5 encapsulated figures. Note added regarding
subsequent related work. To appear in Phys. Rev.
Spectral flow and boundary string field theory for angled D-branes
D-branes intersecting at an arbitrary fixed angle generically constitute a
configuration unstable toward recombination. The reconnection of the branes
nucleates at the intersection point and involves a generalization of the
process of brane decay of interest to non-perturbative string dynamics as well
as cosmology. After reviewing the string spectrum of systems of angled branes,
we show that worldsheet twist superfields may be used in the context of
Boundary Superstring Field Theory to describe the dynamics. Changing the angle
between the branes is seen from the worldsheet as spectral flow with boundary
insertions flowing from bosonic to fermionic operators. We calculate the
complete tachyon potential and the low energy effective action as a function of
angle and find an expression that interpolates between the brane-antibrane and
the Dirac-Born-Infeld actions. The potential captures the mechanism of D-brane
recombination and provides for interesting new physics for tachyon decay.Comment: 32 pages, 9 figures; v2 references added; v3 discussion clarifie
Growth responses of Ailanthus altissima seedlings to SO2
Growth of Ailanthus altissima (Mill.) Swingle seedlings exposed to various levels of sulphur dioxide (SO2) was observed. Exposure for 1 or 2 weeks at 260 [mu]gm-3 (0[middle dot]1 ppm) or 520 [mu]g m-3 (0[middle dot]2 ppm) of SO2 significantly (p 2 concentration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24357/1/0000626.pd
Computational analysis of transitional airflow through packed columns of spheres using the finite volume technique
Copyright © 2010 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Computers and Chemical Engineering. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Computers and Chemical Engineering, Volume 34 Issue 6 (2010), DOI: 10.1016/j.compchemeng.2009.10.013We compare computational simulations of the flow of air through a packed column containing spherical particles with experimental and theoretical results for equivalent beds. The column contained 160 spherical particles at an aspect ratio N=7.14N=7.14, and the experiments and simulations were carried out at particle Reynolds numbers of (RedP=700−5000)(RedP=700−5000). Experimental measurements were taken of the pressure drop across the column and compared with the correlation of Reichelt (1972) using the fitted coefficients of Eisfeld and Schnitzlein (2001). An equivalent computational domain was prepared using Monte Carlo packing, from which computational meshes were generated and analysed in detail. Computational fluid dynamics calculations of the air flow through the simulated bed was then performed using the finite volume technique. Results for pressure drop across the column were found to correlate strongly with the experimental data and the literature correlation. The flow structure through the bed was also analysed in detail
Racetrack Inflation
We develop a model of eternal topological inflation using a racetrack
potential within the context of type IIB string theory with KKLT volume
stabilization. The inflaton field is the imaginary part of the K\"ahler
structure modulus, which is an axion-like field in the 4D effective field
theory. This model does not require moving branes, and in this sense it is
simpler than other models of string theory inflation. Contrary to
single-exponential models, the structure of the potential in this example
allows for the existence of saddle points between two degenerate local minima
for which the slow-roll conditions can be satisfied in a particular range of
parameter space. We conjecture that this type of inflation should be present in
more general realizations of the modular landscape. We also consider
`irrational' models having a dense set of minima, and discuss their possible
relevance for the cosmological constant problem.Comment: 23 pages 7 figures. The final version with minor modifications, to
appear in JHE
Inflating in a Better Racetrack
We present a new version of our racetrack inflation scenario which, unlike
our original proposal, is based on an explicit compactification of type IIB
string theory: the Calabi-Yau manifold P^4_[1,1,1,6,9]. The axion-dilaton and
all complex structure moduli are stabilized by fluxes. The remaining 2 Kahler
moduli are stabilized by a nonperturbative superpotential, which has been
explicitly computed. For this model we identify situations for which a linear
combination of the axionic parts of the two Kahler moduli acts as an inflaton.
As in our previous scenario, inflation begins at a saddle point of the scalar
potential and proceeds as an eternal topological inflation. For a certain range
of inflationary parameters, we obtain the COBE-normalized spectrum of metric
perturbations and an inflationary scale of M = 3 x 10^{14} GeV. We discuss
possible changes of parameters of our model and argue that anthropic
considerations favor those parameters that lead to a nearly flat spectrum of
inflationary perturbations, which in our case is characterized by the spectral
index n_s = 0.95.Comment: 20 pages, 7 figures. Brief discussion on the non-gaussianity of this
model, one more figure of the field trajectories added as well as other minor
changes to the tex
Model Building with Gauge-Yukawa Unification
In supersymmetric theories with extra dimensions, the Higgs and matter fields
can be part of the gauge multiplet, so that the Yukawa interactions can arise
from the gauge interactions. This leads to the possibility of gauge-Yukawa
coupling unification, g_i=y_f, in the effective four dimensional theory after
the initial gauge symmetry and the supersymmetry are broken upon orbifold
compactification. We consider gauge-Yukawa unified models based on a variety of
four dimensional symmetries, including SO(10), SU(5), Pati-Salam symmetry,
trinification, and the Standard Model. Only in the case of Pati-Salam and the
Standard Model symmetry, we do obtain gauge-Yukawa unification. Partial
gauge-Yukawa unification is also briefly discussed.Comment: 23 page
Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events
The - oscillation frequency has been measured with a sample of
23 million \B\bar B pairs collected with the BABAR detector at the PEP-II
asymmetric B Factory at SLAC. In this sample, we select events in which both B
mesons decay semileptonically and use the charge of the leptons to identify the
flavor of each B meson. A simultaneous fit to the decay time difference
distributions for opposite- and same-sign dilepton events gives ps.Comment: 7 pages, 1 figure, submitted to Physical Review Letter
Paragênese mineral de solos desenvolvidos de diferentes litologias na região sul de Minas Gerais
Measurement of the CP-Violating Asymmetry Amplitude sin2
We present results on time-dependent CP-violating asymmetries in neutral B decays to several CP eigenstates. The measurements use a data sample of about 88 million Y(4S) --> B Bbar decays collected between 1999 and 2002 with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We study events in which one neutral B meson is fully reconstructed in a final state containing a charmonium meson and the other B meson is determined to be either a B0 or B0bar from its decay products. The amplitude of the CP-violating asymmetry, which in the Standard Model is proportional to sin2beta, is derived from the decay-time distributions in such events. We measure sin2beta = 0.741 +/- 0.067 (stat) +/- 0.033 (syst) and |lambda| = 0.948 +/- 0.051 (stat) +/- 0.017 (syst). The magnitude of lambda is consistent with unity, in agreement with the Standard Model expectation of no direct CP violation in these modes
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