2,905 research outputs found
Thermal -Brane Boundary States from Green-Schwarz Superstrings
In this paper we thermalize the type II superstrings in the GS formulation by
applying the TFD formalism. The thermal boundary conditions on the thermal
Hilbert space are obtained from the BPS -brane boundary conditions at zero
temperature. We show that thermal boundary states can be obtained by
thermalization from the BPS -branes at zero temperature. These new states
can be interpreted as thermal -branes. Next, we discuss the supersymmetry
breaking of the thermal string in the TFD approach. We identify the broken
supersymmetry with the -transformation while the
-transformation is preserved. Also, we compute the thermal partition
function and the entropy of the thermal string.Comment: 23 pages, LATeX fil
Current Algebra of Super WZNW Models
We derive the current algebra of supersymmetric principal chiral models with
a Wess-Zumino term. At the critical point one obtains two commuting super
Kac-Moody algebra as expected, but in general there are intertwining fields
connecting both right and left sectors, analogously to the bosonic case.
Moreover, in the present supersymmetric extension we have a quadratic algebra,
rather than an affine Lie algebra, due to the mixing between bosonic and
fermionic fields since the purely fermionic sector displays a Lie algebra as
well.Comment: 13 page
Integrable models: from dynamical solutions to string theory
We review the status of integrable models from the point of view of their
dynamics and integrability conditions. Some integrable models are discussed in
detail. We comment on the use it is made of them in string theory. We also
discuss the Bethe Ansatz solution of the SO(6) symmetric Hamiltonian with SO(6)
boundary.
This work is especially prepared for the seventieth anniversaries of
Andr\'{e} Swieca (in memoriam) and Roland K\"{o}berle.Comment: 24 pages, to appear in Brazilian Journal of Physic
Quasinormal modes for the Vaidya metric
We consider here scalar and electromagnetic perturbations for the Vaidya
metric in double-null coordinates. Such an approach allows one to go a step
further in the analysis of quasinormal modes for time-dependent spacetimes.
Some recent results are refined, and a new non-stationary behavior
corresponding to some sort of inertia for quasinormal modes is identified. Our
conclusions can enlighten some aspects of the wave scattering by black holes
undergoing some mass accretion processes.Comment: V2: 6 pages, 5 figure
TFD Approach to Bosonic Strings and -branes
In this work we explain the construction of the thermal vacuum for the
bosonic string, as well that of the thermal boundary state interpreted as a
-brane at finite temperature. In both case we calculate the respective
entropy using the entropy operator of the Thermo Field Dynamics Theory. We show
that the contribution of the thermal string entropy is explicitly present in
the -brane entropy. Furthermore, we show that the Thermo Field approach
is suitable to introduce temperature in boundary states.Comment: 6 pages, revtex, typos are corrected. Prepared for the Second
Londrina Winter School-Mathematical Methods in Physics, August 25-30, 2002,
Londrina-Pr, Brazil. To appear in a special issue of IJMP
Assessment of Plasma Fibrinogen Level and Lipid Profile in Sudanese Smokers
Background: Cigarette smoking is a leading preventable risk factor for the development and progression of cardiovascular diseases (CVDs). Epidemiologic studies in smokers confirm the association between the alteration in lipid profile levels and CVDs risk. Fibrinogen, an acute phase reactant with active involvement in endothelial function, thrombosis and inflammation. It is signified as a systemic marker of carotidatherosclerosis. The purpose of this study was to assess the level of fibrinogen and lipid parameters in Sudanese tobacco smokers.
Methods: This case-control study included 55 adult male of a current smoking status; their ages ranged between 18 and 54 years, and 100 non-smokers considered as controls. We evaluated the effect of cigarette smoking on plasma fibrinogen and serum lipid profile. The American Heart Association guidelines and reference ranges were used to identify the smokers with increased risk of coronary heart disease.
Results: Our study revealed an increase in the levels of fibrinogen, total cholesterol, and low-density lipoprotein cholesterol (LDL-C) among smokers than controls, whereas the mean level of and triglycerides did not differ. The levels of highdensity lipoprotein cholesterol HDL-C demonstrated decrement. Further, smokers were classified according to the atherogenic risk index LDL-C/HDL-C ratio, the studied parameters fibrinogen, total cholesterol, and triglycerides were significantly increased in those who have ratio 4.5 and more (p = 0.001, p = 0.018, p = 0.007, respectively). Smokers with atherogenic index â„ 4.5 were more likely to have â„ 300 mg/dl fibrinogen level (odds ratio (OR) 3.96, 95% confidence interval (95%CI) 1.14â 13.73, p = 0.026). Moreover, the level of the fibrinogen can be predicted by linear regression equation: Fibrinogen level = 19.49 + 79.08 (the ratio of LDL-C âHDL-C), r = 0.37, p = 0.008, 95%CI 21.20â136.95.
Conclusion: Increased fibrinogen, LDL-C, and LDLC/HDL-C ratio may potentiate the development of cardiovascular disease in smokers
Optimising Spectroscopic and Photometric Galaxy Surveys: Efficient Target Selection and Survey Strategy
The next generation of spectroscopic surveys will have a wealth of
photometric data available for use in target selection. Selecting the best
targets is likely to be one of the most important hurdles in making these
spectroscopic campaigns as successful as possible. Our ability to measure dark
energy depends strongly on the types of targets that we are able to select with
a given photometric data set. We show in this paper that we will be able to
successfully select the targets needed for the next generation of spectroscopic
surveys. We also investigate the details of this selection, including
optimisation of instrument design and survey strategy in order to measure dark
energy. We use color-color selection as well as neural networks to select the
best possible emission line galaxies and luminous red galaxies for a
cosmological survey. Using the Fisher matrix formalism we forecast the
efficiency of each target selection scenario. We show how the dark energy
figures of merit change in each target selection regime as a function of target
type, survey time, survey density and other survey parameters. We outline the
optimal target selection scenarios and survey strategy choices which will be
available to the next generation of spectroscopic surveys.Comment: 16 pages, 22 figures, accepted to MNRAS in dec 201
PP-Wave Light-Cone Free String Field Theory at Finite Temperature
In this paper, a real-time formulation of light-cone pp-wave string field
theory at finite temperature is presented. This is achieved by developing the
thermo field dynamics (TFD) formalism in a second quantized string scenario.
The equilibrirum thermodynamic quantities for a pp-wave ideal string gas are
derived directly from expectation values on the second quantized string thermal
vacuum. Also, we derive the real-time thermal pp-wave closed string propagator.
In the flat space limit it is shown that this propagator can be written in
terms of Theta functions, exactly as the zero temperature one. At the end, we
show how supestrings interactions can be introduced, making this approach
suitable to study the BMN dictionary at finite temperature.Comment: 27 pages, revtex
Field propagation in de Sitter black holes
We present an exhaustive analysis of scalar, electromagnetic and
gravitational perturbations in the background of Schwarzchild-de Sitter and
Reissner-Nordstrom-de Sitter spacetimes. The field propagation is considered by
means of a semi-analytical (WKB) approach and two numerical schemes: the
characteristic and general initial value integrations. The results are compared
near the extreme cosmological constant regime, where analytical results are
presented. A unifying picture is established for the dynamics of different spin
fields.Comment: 15 pages, 16 figures, published versio
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