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TOPIC: CBR


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Posts: 131433
Date:
RE: CBR
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Title: Ellipsoidal universe in the brane world
Authors: Xian-Hui Ge, Sang Pyo Kim
(Version v3)

We study a scenario of the ellipsoidal universe in the brane world cosmology with a cosmological constant in the bulk . From the five-dimensional Einstein equations we derive the evolution equations for the eccentricity and the scale factor of the universe, which are coupled to each other. It is found that if the anisotropy of our universe is originated from a uniform magnetic field inside the brane, the eccentricity decays faster in the bulk in comparison with a four-dimensional ellipsoidal universe. We also investigate the ellipsoidal universe in the brane-induced gravity and find the evolution equation for the eccentricity which has a contribution determined by the four- and five-dimensional Newton's constants. The role of the eccentricity is discussed in explaining the quadrupole problem of the cosmic microwave background.

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Posts: 131433
Date:
CPT violation
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Title: Constraints on CPT violation from WMAP three year polarisation data: a wavelet analysis
Authors: Paolo Cabella, Paolo Natoli, Joseph Silk

We perform a wavelet analysis of the temperature and polarisation maps of the Cosmic Microwave Background (CMB) delivered by the WMAP experiment in search for a parity violating signal. Such a signal could be seeded by new physics beyond the standard model, for which the Lorentz and CPT symmetries may not hold. Under these circumstances, the linear polarisation direction of a CMB photon may get rotated during its cosmological journey, a phenomenon also called cosmological birefringence. Recently, Feng et al. have analysed a subset the WMAP and BOOMERanG 2003 angular power spectra of the CMB, deriving a constraint that mildly favours a non zero rotation. By using wavelet transforms we set a tighter limit on the CMB photon rotation angle \Delta\alpha= -2.5 3.0 (\Delta\alpha= -2.5 6.0) at the one (two) \sigma level, consistent with a null detection.

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Posts: 131433
Date:
Inflation
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In the standard model of cosmology, the early universe underwent a period of fantastic growth. This inflationary phase, after only a trillionth of a second, concluded with a violent conversion of energy into hot matter and radiation. This "reheating" process also resulted in a flood of gravitational waves. (Interestingly, some cosmologists would identify the "big bang" with this moment and not the earlier time=0 moment.)
Let's compare this gravitational wave background (GWB) with the more familiar cosmic microwave background (CMB). The GWB dates from the trillionth-of-a-second mark, while the CMB sets in around 380,000 years later when the first atoms formed. The CMB represents a single splash of photons which were (at that early time) in equilibrium with the surrounding atoms-in-the-making; the microwaves we now see in the sky were (before being redshifted to lower frequencies owing to the universe's expansion) ultraviolet waves and were suddenly freed to travel unimpeded through space. They are now observed to be mostly at a uniform temperature of about 3 degrees Kelvin, but the overall map of the microwave sky does bear the faint imprint of matter inhomogeneities (lumps) existing even then.
What, by contrast, does the GWB represent? It stems from three different production processes at work in the inflationary era: waves stemming from the inflationary expansion of space itself; waves from the collision of bubble-like clumps of new matter at reheating after inflation; and waves from the turbulent fluid mixing of the early pools of matter and radiation, before equilibrium among them (known as thermalisation) had been achieved. The gravity waves would never have been in equilibrium with the matter (since gravity is such a weak force there wouldn't be time to mingle adequately); consequently the GWB will not appear to a viewer now to be at a single overall temperature.

A new paper by Juan Garcia-Bellido and Daniel Figueroa (Universidad Autonoma de Madrid) explain how these separate processes could be detected and differentiated in modern detectors set up to see gravity waves, such as LIGO, LISA, or BBO (Big Bang Observer). First, the GWB would be redshifted, like the CMB. But because of the GWB's earlier provenance, the reshifting would be even more dramatic: the energy (and frequency) of the waves would be downshifted by 24 orders of magnitude. Second, the GWB waves would be distinct from gravity waves from point sources (such as the collision of two black holes) since such an encounter would release waves with a sharper spectral signal. By contrast the GWB from reheating after inflation would have a much broader spectrum, centred around 1 hertz to 1 gigahertz depending on the scale of inflation.

Source

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Posts: 131433
Date:
Apparent X-ray Column Density
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Title: Redshift Filtering by Swift Apparent X-ray Column Density
Authors: Dirk Grupe (PSU), John A. Nousek (PSU), Daniel E. vanden Berk (PSU), Peter W.A. Roming (PSU), David N. Burrows (PSU), Neil Gehrels (NASA/GSFC)

We remark on the utility of an observational relation between the absorption column density in excess of the Galactic absorption column density, Delta N_H = N_H,fit - N_H,gal, and redshift, z, determined from all 54 Swift-observed long bursts with spectroscopic redshifts as of 2006 November. The absorption column densities, N_H,fit, are determined from powerlaw fits to the X-ray spectra with the absorption column density left as a free parameter. We find that higher excess absorption column densities are only present in bursts with redshifts z < 3. Low absorption column densities appear preferentially in high-redshift bursts. Our interpretation is that this relation between redshift and excess column density is an observational effect resulting from the shift of the source rest-frame energy range below 1 keV out of the XRT observable energy range. We found a clear anti-correlation between Delta N_H and z that can be used to limit the range of the maximum redshift of an afterglow. A critical application of our finding is that rapid X-ray observations can be used to optimise ground-based optical/NIR follow-up observations.

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Posts: 131433
Date:
RE: CBR
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Title: Probing trans-Planckian physics and the curvature effect from primordial power spectrum with WMAP 3 observations
Authors: Jie Ren, Hong-Guang Zhang, Xin-He Meng
(revised v2)

In this work the vacuum inflation with a boundary condition specified at a short-distance scale in a generally primeval non-flat Universe, and implications of the correspondingly modified primordial power spectrum via the WMAP three year data are investigated. We obtain a general form of the modified primordial power spectrum including the effects of both possibly new physics and the curvature term. The modulation of the primordial power spectrum due to new physics is of the order H/\Lambda, where H is the Hubble parameter during inflation and \Lambda is the new physics scale that is key to inflation, while the modulation from the curvature term is of the order K/k, where K is the space curvature before inflation and k is the comoving wave number. We add two more parameters, which describe the effects from new physics scale and the curvature term respectively, into the six-parameter standard model of cosmology and make a fitting analysis with the WMAP data sets. The result shows that new physics would appear around the GUT scale and a closed Universe before inflation is slightly favoured by the data fittings.

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Posts: 131433
Date:
MAXIPOL
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Title: MAXIPOL: Data Analysis and Results
Authors: J. H. P. Wu, J. Zuntz, M. E. Abroe, P. A. R. Ade, J. Bock, J. Borrill, J. Collins, S. Hanany, A. H. Jaffe, B. R. Johnson, T. Jones, A. T. Lee, T. Matsumura, B. Rabii, T. Renbarger, P. L. Richards, G. F. Smoot, R. Stompor, H. T. Tran, C. D. Winant

We present results from and the analysis of data from MAXIPOL, a balloon-borne experiment designed to measure the polarisation in the Cosmic Microwave Background (CMB). MAXIPOL is the first CMB experiment to obtain results using a rotating half-wave plate as a rapid polarisation modulator. We report results from observations of a sky area of 8 deg with 10-arcmin resolution, providing information up to l~700. We use a maximum-likelihood method to estimate maps of the Q and U Stokes parameters from the demodulated time streams, and then both Bayesian and frequentist approaches to compute the EE, EB, and BB power spectra. Detailed formalisms of the analyses are given. A variety of tests show no evidence for systematic errors. The Bayesian analysis gives weak evidence for an EE signal. The EE power is 55^+51_-45 K at the 68% confidence level for l=151-693. Its likelihood function is asymmetric and skewed positive such that with a uniform prior the probability of a positive EE power is 96%. The powers of EB and BB signals at the 68% confidence level are 18^+27_-34 K and -31^+31_-19 K respectively and thus consistent with zero. The upper limit of the BB-mode at the 95% confidence level is 9.5 K. Results from the frequentist approach are in agreement within statistical errors. These results are consistent with the current concordance LCDM model.

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Posts: 131433
Date:
Highest-energy cosmic rays
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Controversy abounds over how to explain the highest-energy cosmic rays, subatomic particles that tear through space at near light speed while packing the punch of rifle bullets. Now a cosmic ray detector in Utah has further deepened the controversy with evidence that the particles may not be so powerful after all.
A new analysis of results from the High Resolution Fly's Eye (HiRes) experiment in Salt Lake City has detected a sharp cut-off in the energy spectrum of cosmic rays. This stands in stark contrast to a Japanese experiment that has previously reported particles with bafflingly higher energies.
According to standard physics, cosmic rays with energies larger than about 5 10^19 electronvolts will collide with photons left over from the big bang and so lose energy as they cross large distances. This puts a theoretical limit on the energy they can have when they reach Earth

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Posts: 131433
Date:
Cosmic Microwave Background anisotropies
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Title: Cosmic Microwave Background anisotropies: the power spectrum and beyond
Authors: Enrique Martinez-Gonzalez

Most of the cosmological information extracted from the CMB has been obtained through the power spectrum, however there is much more to be learnt from the statistical distribution of the temperature random field. We review some recent developments in the study of the Cosmic Microwave Background (CMB) anisotropies and present a description of the novel tools developed to analyse the properties of the CMB anisotropies beyond the power spectrum.

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Posts: 131433
Date:
2006 Nobel Physics Prize
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Two US scientists, John C Mather and George F Smoot, have won the 2006 Nobel Physics Prize.

They have been honoured "for their discovery of the blackbody form and anisotropy of the cosmic microwave background radiation (CMB)".

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Posts: 131433
Date:
CMB Quadrupole Problem
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In March, WMAP scientists released additional data, which showed remarkable agreement with the simplest inflationary models of the Big Bang. Everything looks the way inflation suggests it should except at the largest possible angular scale that of the whole sky, more properly termed the quadrupole moment.

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