Superstrings - Astronomy News

Blobrana

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Posts: 131433

Date: Aug 2 15:49 2007

The Standard Model	Permalink

Presentation by Joe Lykken __________________

Blobrana

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Posts: 131433

Date: Jul 28 14:15 2007

RE: Superstrings	Permalink

Introduction to the M-Theory. Montage from "Horizon" (BBC/TLC 2002) __________________

Blobrana

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Posts: 131433

Date: Jul 6 02:00 2007

Black ring formation	Permalink

Title: Collision of high-energy closed strings: Black ring formation Authors: Hirotaka Yoshino, Tetsuya Shiromizu We study collisions of two high-energy closed strings in the framework of D-dimensional general relativity. The model of a high-energy closed string is introduced as a pp-wave generated by a ring-shaped source with the radius R. At the instant of the collision, the positions of two strings are assumed to coincide precisely. In this setup, we study the formation of two kinds of apparent horizons (AHs): the AH of topology S^{D-2} (the black hole AH) and the AH of topology S^1 x S^{D-3} (the black ring AH). These two AHs are solved numerically and the conditions for the formation of the two AHs are clarified in terms of the ring radius R. Specifically, we demonstrate that the black ring AH forms for sufficiently large R. The effects of an impact parameter and the relative orientation of incoming strings in more general cases are briefly discussed. Read more (156kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Jun 26 12:54 2007

Particle Cosmology	Permalink

Constraints and Signatures in Particle Cosmology If you are really lucky, then you may have a great new idea about particle physics. It may be a way to address the hierarchy problem (why is gravity so much weaker then the known particle physics forces), or to generate mass for fermions (after all, we havent found the Higgs yet), or to understand the flavour hierarchy (how come there are three repeated families of particles in the standard model with increasing masses), or perhaps to unify all the forces into one (Grand Unification). Obviously, your obligation is to begin systematically computing the consequences of this idea for existing and future particle physics experiments. Thirty years or so ago, with a few notable exceptions this would have been the end of the story. But it has become increasingly clear to most physicists that there exists a complementary list of consequences that should be figured out; those for cosmology. These days, this approach is basically second nature to any of us who might have new ideas about how the micro-world works, and reflects the modern thinking that particle physics and cosmology are not distinct disciplines, but are two sides of the same set of questions. Read more __________________

Blobrana

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Posts: 131433

Date: Jun 25 18:35 2007

RE: Superstrings	Permalink

NASA is funding the development of lasers that could be placed on the Moon to check for subtle deviations from the standard theory of gravity. Lasers have been used to make very precise measurements of the Earth-Moon distance since the Apollo era, when astronauts left reflectors at three sites on the lunar surface. A fourth reflecting device is attached to a robotic lunar lander launched by the Soviet Union. To pin down the Moon's distance, scientist bounce light from Earth-based lasers off of these reflectors and measure how long it takes to return. Because the Moon's motion is governed by gravity, such studies can be used to test whether Einstein's general theory of relativity gives an accurate description of this motion. Some speculative theories of cosmology, such as one inspired by string theory that involves exotic particles called dilatons, predict deviations from general relativity. Other theories predict that the gravitational constant (G), which measures the basic strength of gravity, is not constant at all, but varies with time. These deviations are predicted to be very subtle, so more precise measurements are needed to either detect them or rule them out. Read more __________________

Blobrana

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Posts: 131433

Date: Jun 24 14:02 2007

Weird extra-spatial dimensions	Permalink

If the universe has weird extra-spatial dimensions in parallel to the 3D world we see around us, then billion-dollar particle accelerators may not be the only place to find them. So say Gergely Gabor Barnaföldi and colleagues at the Research Institute for Particle and Nuclear Physics in Budapest, Hungary, who propose that extra dimensions may show their face in areas of extreme gravity around dense stars. The concept could also solve a 25-year-old puzzle about the origin of mysterious particles emanating from a distant star system. Some string theories predict that there are many more dimensions than the four we experience: the 3D world plus time. From next year, particle physicists hope to spot these dimensions at the Large Hadron Collider near Geneva, Switzerland. Instead, Barnaföldi's team looked to outer space for evidence of extra dimensions interacting with matter. They analysed the Cygnus X-3 binary system, in which a normal star orbits a second object, generally thought to be a neutron star. Read more __________________

Blobrana

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Posts: 131433

Date: May 31 05:12 2007

RE: Superstrings	Permalink

Title: Brane Cosmology and KK Gravitinos Authors: C. Bambi, F.R. Urban The cosmology of KK gravitinos in models with extra dimensions is considered. The main result is that the production of such KK modes is not compatible with an epoch of non--standard expansion after inflation. This is so because the BBN constraint on the zero mode forces the reduced five dimensional Planck mass M_5 down to values much smaller than the usual four dimensional one, but this in turn implies many KK states available for a given temperature. Once these states are taken into account one finds that there is no M_5 for which the produced KK gravitinos satisfy BBN and overclosure constraints. This conclusion holds for both flat and warped models in which only gravity propagates in the full spacetime. Read more (17kb, PDF) __________________

Blobrana

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Posts: 131433

Date: May 23 11:12 2007

Brane-antibrane Inflation	Permalink

Title: Fine-Tuning in Brane-antibrane Inflation Authors: James M. Cline I give a brief overview of brane-antibrane inflation, with emphasis on the problems of tuning to get a flat potential in the KKLMMT framework, and recent work on the nature of superpotential corrections in that model. Read more (135kb, PDF) __________________

Blobrana

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Posts: 131433

Date: May 9 11:34 2007

Parallel Universes	Permalink

BBC Documentary - Horizon 2002 - Parallel Universes Scientists now believe there may really be a parallel universe - in fact, there may be an infinite number of parallel universes, and we just happen to live in one of them. These other universes contain space, time and strange forms of exotic matter. Some of them may even contain you, in a slightly different form. Astonishingly, scientists believe that these parallel universes exist less than one millimetre away from us. In fact, our gravity is just a weak signal leaking out of another universe into ours. See more __________________

Blobrana

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Posts: 131433

Date: May 3 20:50 2007

String theory	Permalink

Princeton physicists connect string theory with established physics String theory, simultaneously one of the most promising and controversial ideas in modern physics, may be more capable of helping probe the inner workings of subatomic particles than was previously thought, according to a team of Princeton University scientists. The theory has been highly praised by some physicists for its potential to forge the long-sought link between gravity and the forces that dominate within the atomic nucleus. But the theory -- which posits that all subatomic particles are actually tiny "strings" that vibrate in different ways -- has also drawn criticism for being untestable in the laboratory, and perhaps impossible to connect with real-world phenomena. However, the Princeton researchers have found new mathematical evidence that some of string theory's predictions mesh closely with those of a well-respected body of physics called "gauge theory," which has been demonstrated to underlie the interactions among quarks and gluons, the vanishingly small objects that combine to form protons, neutrons and other, more exotic subatomic particles. The discovery, say the physicists, could open up a host of uses for string theory in attacking practical physics problems. Read more __________________

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