This Week in the Universe: September 28th – October 4th

Astrophysics and Gravitation:

Vacuum-Driven Evolution in Astrophysics

William C. C. Lima, George E. A. Matsas, & Daniel A. T. Vanzella (2010). Awaking the vacuum in relativistic stars Physical Review Letters arXiv: 1009.1771v1

In a very cool paper that will be appearing in the Physical Review Letters at the end of the week, Lima et al. have shown an interesting (and surprising) relationship between neutron star formation and the vacuum energy density of our universe. Using some semi-classical concepts of gravity [PRL 104, 161102 (2010)], the authors come the conclusion that the formation of relativistic, compact, objects (like neutron stars) could disturb the vacuum of a quantum field (of a certain type) which could cause the energy density of the vacuum to undergo exponential growth.  This growth could eventually lead to the collapse or explosion of the relativistic object in question.  Of course, the observation of stable neutron stars should be suggestive that such fields (that could have triggered this exponential growth in energy density) can not exist.  Thus, if we see stable neutron stars (which we think we do), we learn something about the vacuum state of the universe, ie. the observation of a stable and (reasonably) spinless cold neutron star would rule out the existence of massless scalar fields with a range of coupling constants.  Seeing as we only know what a marginal fraction of the universe’s energy content is, this could prove incredibly useful for the field theoretically inclined cosmologists out there.  The nitty-gritty details on what should specifically happen to these relativistic objects hasn’t been worked out just yet (I’m sure someone will be donating some cluster time soon), but when it has, we may end up learning something new and exciting about one of the most basic aspects of our universe.

For more, see Neutron Star Formation Could Awaken the Vacuum.

High Energy Physics and Particles:

Randomness Brings Order to Quarks

P. H. Damgaard, K. Splittorff, & J. J. M. Verbaarschot (2010). Microscopic Spectrum of the Wilson Dirac Operator arXiv arXiv: 1001.2937v3

An interesting paper out of the Niels Bohr Institute shows how large quantities of random numbers can help explain the oscillations of quarks within protons.

Kim Splittorff:

Over several years it became increasingly clear that the way in which the left-handed and right-handed quarks come together can be described using a massive quantities of random numbers. These random numbers are elements in a matrix, which one may think of as a Soduko filled in at random. In technical jargon these are called Random Matrices.

Random numbers have been used for quite some time to make sense of spontaneous symmetry breaking, but what is unique about this team’s work is that they are doing it exactly.


What is new about our work is that not only the exact equation for quarks, but also the approximation, which researchers who work numerically have to use, can be described using random matrices. It is already extremely surprising that the exact equation shows that the quarks swing by random numbers. It is even more exciting that the approximation used for the equation has a completely analogous description. Having an accurate analytical description available for the numerical simulations is a powerful tool that provides an entirely new understanding of the numerical data. In particular, we can now measure very precisely how closely the right-handed and left-handed quarks are dancing

How “exact” this really can be, is more of a philosophical question at this point, but this technique will find use in helping make predictions at CERN and even in condensed matter systems.

For more, see Quarks ‘swing’ to the tones of random numbers.

General Relativity, Quantum Gravity, et al.:

Hawking Radiation, Observed?

F. Belgiorno, S. L. Cacciatori, M. Clerici, V. Gorini, G. Ortenzi, L. Rizzi, E. Rubino, V. G. Sala, & D. Faccio (2010). Hawking radiation from ultrashort laser pulse filaments arXiv arXiv: 1009.4634v1

I have lengthy comments to make on this paper that will appear later this week, but it is a fascinating (and short) read.

The abstract:

Event horizons of astrophysical black holes and gravitational analogues have been predicted to excite the quantum vacuum and give rise to the emission of quanta, known as Hawking radiation. We experimentally create such a gravitational analogue using ultrashort laser pulse filaments and our measurements demonstrate a spontaneous emission of photons that confirms theoretical predictions.

Did they really observe Hawking radiation? That’s a question that will be open for debate for quite some time.

For more, see Physicists may have observed Hawking radiation for the first time, Imitation black hole seen on earth.

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