terça-feira, 16 de fevereiro de 2016

Quark-Gluon Plasma Can Be Described by Five-Dimensional Black Hole

Hello reader!

Below is an article published the day (02/10) in the website of the "Agency FAPESP", noting that Quark-Gluon Plasma can be described by Five-Dimensional Black Hole.

Duda Falcão


Quark-Gluon Plasma Can Be Described
By Five-Dimensional Black Hole

By José Tadeu Arantes
Agência FAPESP
February 10, 2016

(Image: Brookhaven National Laboratory, 
taken on March 20, 2012)
Event display of a single collision of gold ions accelerated to
200 giga-electron-volts (GeV), as measured by the silicon vertex
tracker of the PHENIX detector at the Relativistic Heavy Ion
Collider (RHIC) in the United States

Researchers at the University of São Paulo’s Physics Institute (IF-USP) in Brazil and Columbia University’s Department of Physics in the United States have used computer simulations to quantitatively determine for the first time how baryon charge travels through the quark-gluon plasma produced in the world’s largest particle colliders. Baryon charge is the difference between the number of quarks and antiquarks in a given medium.

An article describing their study, “Suppression of Baryon Diffusion and Transport in a Baryon Rich Strongly Coupled Quark-Gluon Plasma”, has been published in Physical Review Letters. The paper is authored by Rômulo Rougemont and Jorge Noronha from IF-USP and Jacquelyn Noronha-Hostler from Columbia.

Their research was supported by FAPESP through a postdoctoral scholarship awarded to Rougemont to study “Computation of the properties of quark-gluon plasma at non-zero temperature and baryon density using holographic correspondence”, with Noronha as supervisor, and through a scholarship abroad awarded to Noronha to study “Dynamic aspects of strongly coupled quark-gluon plasma”.

Quark-gluon plasma is believed to have predominated in the universe for a tiny fraction of a second after the Big Bang, well before the expansion and cooling of the universe reconfigured its matter and energy several times, until it reached its present state. If the direction of this process is inverted, it is possible to produce quark-gluon plasma from ordinary matter by heating it to temperatures thousands of times hotter than the highest temperature in the sun.

On earth, however, this can be done only in high-energy collisions of protons with heavy nuclei at ultrarelativistic velocities (close to the speed of light), and even so only for an instant. The only laboratories capable of performing such feats are the Large Hadron Collider (LHC) in Europe and the Relativistic Heavy Ion Collider (RHIC) in the US.

“By simulating on a computer the properties of 250,000 five-dimensional black holes, we calculated how baryons propagate through quark-gluon plasma when the system contains more matter than antimatter,” Noronha told Agência FAPESP. “To do this, we used a theoretical model based on holographic duality, which establishes a surprising equivalence between certain quantum theories defined in usual spacetime and superstring physics in curved spacetime with five extended dimensions.”

Holographic Duality

Holographic duality, discovered by Argentinian physicist Juan Maldacena in 1997, is considered one of the most groundbreaking ideas to emerge from theoretical physics in recent years because it enables certain quantum phenomena that are hard to understand in usual spacetime, which has four dimensions, to be studied as holograms of simpler gravitational phenomena that occur in five dimensions.

These five-dimensional phenomena are described by superstring theory, which is currently the leading candidate for quantum gravity theory and could therefore solve the hitherto insoluble problem of making quantum theory compatible with general relativity, the other pillar of contemporary physics. Advocates of superstring theory believe it could play a key role in the understanding of configurations in which matter/energy is compressed to extreme densities, as in the primordial universe or in the interior of a black hole.

“Superstring theory contends that the fundamental particles we’ve identified in the universe in fact correspond to different modes of vibration of minute strings that exist in ten-dimensional spacetime,” Noronha explained. “Because the universe to which we have access by means of observational instruments and experiments presents itself as spacetime with four extended dimensions [the three dimensions of space plus time], the hypothesis is that the six additional dimensions posited by superstring theory must be compacted in very minute objects, which we can’t probe directly with the technology we have now.”

In principle, there are a great many possible compactions for the extra dimensions, and each would correspond to a different universe. The universe we know would be just one of these many possible universes.

“What Maldacena discovered was an important mathematical relationship between certain quantum theories defined for usual flat spacetime, with four extended dimensions; superstrings existing in a context formed by the composition of curved spacetime with five extended dimensions [called anti-de Sitter space]; and a hypersphere with five compacted dimensions. The mathematical relationship discovered by Maldacena is called the holographic duality,” Noronha said.

One of the main applications of the holographic duality consists of using the physical properties of black holes defined in a five-dimensional anti-de Sitter (AdS) space to approximately calculate the characteristics of quark-gluon plasma produced experimentally in the LHC and RHIC.

“The expression ‘quark-gluon plasma’ calls for some explanation,” Noronha went on. “Plasma is gas made up of ions, which are electrically charged particles, whereas gluons are neutral and quarks have fractional charges, unlike all other particles, which have integer or zero charges.

“Another peculiarity of quarks and gluons is that under the conditions habitually observed in nature these fundamental particles are confined within hadrons, a family of composite particles that includes protons and neutrons, which make up the atomic nucleus. When heavy atomic nuclei made up of several protons and neutrons collide at very high energy levels, as they do in the LHC and RHIC, quarks and gluons are temporarily released, forming the medium we call quark-gluon plasma for the sake of convenience.

“In fact, this ‘plasma’ consists of tiny droplets with a radius of about 10-15 m at very high temperatures about 250,000 times hotter than the core of the sun, estimated at 107 Kelvin. These droplets formed in the large colliders constitute the most perfect, smallest and hottest fluid ever made by man. They last only a fraction of a second, and then cooling binds the quarks and gluons back into hadrons again. This medium is believed to correspond to the condition of the universe a few microseconds after the Big Bang.”

The paper by Rougemont, Noronha and Noronha-Hostler published in Physical Review Letters describes how they used the holographic duality and computer simulations to investigate baryon diffusion through quark-gluon plasma for the first time in the literature and how they calculated the conductivity associated with baryon charge, as well as other observable magnitudes that are extremely important for the physical characterization of this state of matter.

The paper “Suppression of Baryon Diffusion and Transport in a Baryon Rich Strongly Coupled Quark-Gluon Plasma” (http://dx.doi.org/10.1103/PhysRevLett.115.202301) by Rômulo Rougemont, Jorge Noronha and Jacquelyn Noronha-Hostler, can be read in Physical Review Letters, available online at http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.202301.

Source: Website of the Agência FAPESP - http://agencia.fapesp.br/

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