Big Bang Parte 2: a segunda inflação

Big bang, part 2: the second inflation

19 May 2010 by Rachel Courtland

Magazine issue 2761.

DID the big bang boil? The birth of our universe could have seethed with hot bubbles and, perhaps, a second period of rapid expansion. Such an episode may have left an imprint on the universe that persists to this day and might mean we're on the wrong track in our hunt for dark matter.

Just 10-37 seconds or so after its birth, a period of inflation is thought to have caused the universe to balloon in size. This process is thought to have amplified tiny quantum fluctuations in the vacuum, giving rise to the megastructures we see all around us in the universe today.

A second profound transformation is thought to have followed hot on the heels of inflation. Just microseconds old and at trillions of degrees, the universe condensed from a superhot soup of sub-nuclear particles called a quark-gluon plasma (QGP) into particles such as protons and neutrons. But exactly how this happened is far from clear.

Double bubble (Image: Detlev Van Ravenswaay/SPL)

Decades ago, physicists suspected the change could have been abrupt and violent. In that scenario, the universe expands through inflation, then the QGP cools down to the point that bubbles spontaneously start to form. These bubbles release spectacular amounts of energy once stored in the vacuum, and particles composed of quarks and gluons are formed. The idea was attractive, not least because as these bubbles collided and merged, their interaction could have sown the seeds of intergalactic magnetic structures that persist today but whose origins are a mystery.

Yet computer simulations of conditions in the early universe soon began to hint that the transition from the superhot QGP to the matter we see today wasn't nearly so dramatic. This culminated in 2006, when Yasumichi Aoki, then at the University of Wuppertal in Germany, and colleagues, reported the results of rigorous simulations that showed that the transition must have been smooth. "That was supposed to be the final word on the subject," says Thomas Schaefer of North Carolina State University in Raleigh.

Now some physicists are arguing that we ought to reconsider whether the cosmos had a bubbly "boiling" birth after all: new analyses suggest the QGP could have bubbled violently as it cooled and might even have been preceded by an additional phase of rapid expansion of the universe.

Aoki and colleagues had simulated a QGP in which matter and antimatter are found in equal amounts. That closely matches conditions in the early universe, which is thought to have contained a billion-and-one particles of matter for every billion particles of antimatter. Almost all of these particles annihilated each other, leaving the relatively small amount of matter that makes up all the stars and galaxies we see today.

Yet last year, Dominik Schwarz and Maik Stuke at Bielefeld University in Germany calculated that the universe could have bubbled and boiled if the initial number of leptons - particles which are not made of quarks, such as electrons and neutrinos - was sufficiently higher than their antiparticle partners (Journal of Cosmology and Astroparticle Physics, DOI: 10.1088/1475-7516/2009/11/025).

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Read more here/Leia mais aqui: New Scientist

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Journal of Cosmology and Astroparticle Physics

Lepton asymmetry and the cosmic QCD transition

Author

Dominik J. Schwarz and Maik Stuke

Affiliations

Fakultät für Physik, Universität Bielefeld, Postfach 100131, 33501 Bielefeld, Germany

E-mail dschwarz@physik.uni-bielefeld.de mstuke@physik.uni-bielefeld.deJournal

Journal of Cosmology and Astroparticle Physics Create an alert RSS this journalmonth

Volume 2009, November 2009 Citation

Dominik J. Schwarz and Maik Stuke JCAP11(2009)025

doi: 10.1088/1475-7516/2009/11/025

Abstract

We study the influence of lepton asymmetries on the evolution of the early Universe. The lepton asymmetry l is poorly constrained by observations and might be orders of magnitudes larger than the observed baryon asymmetry b 10−10, |l|/b ≤ 2 × 108. We find that lepton asymmetries that are large compared to the tiny baryon asymmetry, can influence the dynamics of the QCD phase transition significantly. The cosmic trajectory in the μB−T phase diagram of strongly interacting matter becomes a function of lepton (flavour) asymmetry. For tiny or vanishing baryon and lepton asymmetries lattice QCD simulations show that the cosmic QCD transition is a rapid crossover. However, for large lepton asymmetry, the order of the cosmic transition remains unknown.

Keywords   cosmological phase transitions   physics of the early universe

E-print Number: 0906.3434

Cited: by |

Refers: toPACS

98.80.Cq Particle-theory and field-theory models of the early Universe (including cosmic pancakes, cosmic strings, chaotic phenomena, inflationary universe, etc.)

11.30.Fs Global symmetries (e.g., baryon number, lepton number)

12.38.Bx Perturbative calculations

95.30.Cq Elementary particle processesSubjects

Gravitation and cosmology

Particle physics and field theory

Astrophysics and astroparticles Dates

Issue 11 (November 2009)

Received 2 Julho 2009 , accepted for publication 5 Novembro 2009

Published 25 Novembro 2009

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