A precisão psicofísica

Olinto, Lidia

doi:10.47749/t/unicamp.2012.879683

Cited by 3 publications

(3 citation statements)

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“…If large-scale magnetic fields are present throughout the universe today, their structure and spectrum should bear clearer signatures of their past. Thus, improved direct observations, such as high resolution Faraday rotation maps and the study of extragalactic cosmic rays, may help in this respect [6]. For example, we would like to know whether or not the intergalactic voids are permeated by a widespread magnetic field, and whether there is magnetic field evolution in galaxies.…”

Section: Introductionmentioning

confidence: 99%

Magnetized cosmological perturbations

2000

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The aim of these lecture notes is to familiarize graduate students and beginning postgraduates with the basic ideas of linear cosmological perturbation theory and of structure formation scenarios. We present both the Newtonian and the general relativistic approaches, derive the key equations and then apply them to a number of characteristic cases. The gauge problem in cosmology and ways to circumvent it are also discussed. We outline the basic framework of the baryonic and the non-baryonic structure formation scenarios and point out their strengths and shortcomings. Fundamental concepts, such as the Jeans length, Silk damping and collisionless dissipation, are highlighted and the underlying mathematics are presented in a simple and straightforward manner. IntroductionLooking up into the night sky we see structure everywhere. Star clusters, galaxies, galaxy clusters, superclusters and voids are evidence that on small and moderate scales, that is up to 10 Mpc, our universe is very lumpy. As we move to larger and larger scales, however, the universe seems to smooth out. This is evidenced by the isotropy of the x-ray background, the number counts of radio sources and, of course, by the high isotropy of the Cosmic Microwave Background (CMB) radiation. The latter also provides a fossil record of our observable universe when it was roughly 10 5 years old and about 10 3 times smaller than today. So, the universe was very smooth at early times and it is very lumpy now. How did this happen? Although the details are still elusive, cosmologists believe that the reason is "gravitational instability". Small fluctuations in the density of the primeval cosmic fluid that grew gravitationally into the galaxies, the clusters and the voids we observe today. The idea of gravitational instability is not new. It was first introduced in the early 1900s by Jeans, who showed that a homogeneous and isotropic fluid is unstable to small perturbations in its density [1]. What Jeans demonstrated was that density inhomogeneities grow in time when the pressure support is weak compared to the gravitational pull. In retrospect, this is not surprising given that gravity is always attractive. As long as pressure is negligible, an overdense region will keep accreting material from its surroundings, becoming increasingly unstable until it eventually collapses into a gravitationally bound object. Jeans, however, applied his analysis to a static Newtonian fluid in an attempt to understand * e-mail address: ctsagas@maths.uct.ac.za 1 the formation of planets and stars. In modern cosmology we need to account for the expansion of the universe as well as for general relativistic effects.Despite the lack, as yet, of a detailed scenario, the rather simple idea that the observed structure in our universe has resulted from the gravitational amplification of weak primordial fluctuations seems to work remarkably well. These small perturbations grew slowly over time until they were strong enough to separate from the background expansion, turn around, and c...

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Section: Introductionmentioning

confidence: 99%

Magnetized cosmological perturbations

2000

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“…The observation of cosmic high to ultrahigh energy neutrinos with energies above 1 TeV is one of the important challenges of cosmic ray detectors in order to probe the faintest regions of the Universe, i.e., astrophyics phenomena such as galaxy formation as well as particle (possibly 'new') physics. The sources of cosmic (anti)neutrinos range, however, from the well established to the highly speculative [1,2,3,4,5], such as active galactic nuclei (AGN) [6,7,8], gamma ray bursts (GRB) [9], decays of exotic heavy particles of generic top-down or topological defects (TD) [10,11,12,13,14] and Z-bursts [15,16,17,18]. Representative fluxes of some of these hypothesized sources are displayed in Fig.…”

Section: Introductionmentioning

confidence: 99%

Signatures of cosmic tau neutrinos

Reya

Rödiger

2005

Phys. Rev. D

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The importance and signatures of cosmic tau-(anti)neutrinos have been studied for upward-and downward-going µ − + µ + and hadronic shower event rates relevant for present and future underground water or ice detectors, utilizing the unique and reliable ultrasmall-x predictions of the dynamical (radiative) parton model. The upward-going µ − + µ + event rates calculated just from cosmic ν µ + νµ fluxes are sizeably enhanced by taking into account cosmic ν τ + ντ fluxes and their associated τ − + τ + fluxes as well. The coupled transport equations for the upward-going (−) ν τ flux traversing the Earth imply an enhancement of the attenuated and regenerated (−) ν τ flux typically around 10 4 − 10 5 GeV with respect to the initial cosmic flux.This enhancement turns out to be smaller than obtained so far, in particular for flatter initial cosmic fluxes behaving like E −1 ν . Downward-going µ − +µ + events and in particular the background-free and unique hadronic 'double bang' and 'lollipop' events allow to test downward-going cosmic ν τ + ντ fluxes up to about 10 9 GeV.

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“…Ref. [15]). A further objection against this proposal is the mismatch in the energy fluxes of observed UHECRs and of the potential sources as well as the lack of spatial correlations between observed UHECRs and candidate sources (see e.g.…”

Section: Introductionmentioning

confidence: 99%

Threshold Effects and Lorentz Symmetry

Bertolami¹

2003

Decoherence and Entropy in Complex Systems

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Evidence on the violation of Lorentz symmetry arises from the observation of cosmic rays with energies beyond the GZK cutoff, $E_{GZK} \simeq 4 \times 10^{19} eV$, from the apparent transparency of the Universe to the propagation of high energy gamma radiation and from the stability of pions in air showers. These three paradoxes can be explained through deformations of the relativistic dispersion relation. Theoretical ideas aimed to understand how Lorentz symmetry may be broken and phenomenologically interesting deformations of the relativistic dispersion relation may arise are briefly discussed.Comment: 7 pages. Talk presented at the ``Decoherence, Information, Complexity and Entropy 2002'', Piombino, Italy, September 200

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A precisão psicofísica

Cited by 3 publications

References 0 publications

Magnetized cosmological perturbations

Magnetized cosmological perturbations

Signatures of cosmic tau neutrinos

Threshold Effects and Lorentz Symmetry

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