## Friday, December 12, 2008

### Holographic Baryons

Today I came across a nice talk by Shigeki Sugimoto entitled Properties of Baryons in Holographic QCD. Using Gauge/String duality, the talk explores the implications of modeling baryons as wrapped D4-branes or equivalently, instantons on D8-branes. The talk is largely based on the pre-print arXiv:0806.3122.

## Tuesday, December 09, 2008

### Status of Superstring and M-Theory

A new paper, entitled "Status of Superstring and M-Theory" has recently appeared on the arxiv, written by none other than one of the fathers of string theory, John H. Schwarz. The paper is very readable and covers the history of string theory, as well as the dualities that imply the existence of an 11-dimensional M-theory underlying the various string theories and supergravity. Other topics include Flux Compactifications, Warped Compactification, Brane Worlds, String Cosmology, M-theory on G2-Manifolds and F-theory Local Models.

F-theory phenomenology (pioneered by Vafa et al) is one of the promising approaches toward connecting stringy physics to the standard model. John explains that "[t]he new proposal, which has given the subject a new lease on life, is to focus on models in which one can define a limit in which gravity is decoupled. The criterion is that it should be possible to make the dimensions transverse to the 4-cycles wrapped by the 7-branes arbitrarily large. Equivalently, it should be possible to contract the 4-cycles to points while holding the six-dimensional volume fixed. Such contractible 4-cycles must be positive curvature Kahler manifolds. These are fully classified and are given by manifolds called del Pezzo manifolds (or del Pezzo surfaces), which are denoted dP_n. The integer n takes the values 0 ≤ n ≤ 8.9 The del Pezzos have a close relationship with the exceptional Lie algebras E_n. The basic idea is that they contain 2-cycles whose intersections are characterized by the E_n Dynkin diagram. By this type of F-theory construction, one can construct an SU(5) or SO(10) SUSY-GUT model. Constructions that involve 7-branes of various types are much more subtle – and also more interesting than ones that only involve D7-branes. D7-branes are mutually local. A stack of N of them gives U(N) gauge symmetry. Matter fields at intersections (due to stretched open strings) are bifundamental. However, different kinds of 7-branes are mutually nonlocal. As a result, there are stacks (corresponding to the ADE classification of singularities) that can give U(N), SO(2N) or even E_N gauge symmetry."

So we see that F-theory, along with the use of del Pezzo surfaces enhances the usual symmetry groups one recoveres from stacks of branes. (Such symmetry groups describe the freedom the string has in choosing which brane in the stack to end on.) Phenomenologically, a configuration with E_6 symmetry would be particularly interesting.

## Saturday, November 22, 2008

### Meteor Lights up Western Canada Skies

The meteor that streaked through the darkening skies over Alberta and Saskatchewan at about 5:30 p.m. Calgary time, likely weighed between one and 10 tons and shone brightly enough to be seen over an area 700 km (435 miles) wide.

Alan Hildebrand (a planetary scientist at the University of Calgary) said the meteor may have broken into hundreds of smaller meteorites that likely landed in central Saskatchewan near that province's border with Alberta.

## Monday, October 13, 2008

### Black Holes, Qubits and Octonions

In perhaps what is the most up-to-date paper on the quantum computation-extremal black hole-division algebra correspondence, Duff et al review all previous conjectures and suggest an alternative interpretation for which the black hole charges are identified with components of reduced density matrices. The density matrix formulation of quantum mechanics is discussed and compared to the Jordan algebraic quantum mechanics, showing the two approaches are essentially equivalent. The exceptional Jordan algebra forbids a traditional Hilbert space formulation, hence the corresponding D=5 and D=4 supergravities remain somewhat of a mystery.

## Wednesday, September 10, 2008

### LHC First beam a success

Today, the first beam in the Large Hadron Collider (LHC) at CERN was successfully steered around the full 27 kilometres of the world’s most powerful particle accelerator this morning.

“It’s a fantastic moment,” said LHC project leader Lyn Evans, “we can now look forward to a new era of understanding about the origins and evolution of the universe.”

The LHC is capable of proping the energy region around 1 TeV by colliding together 7 TeV proton beams, which should reveal new physics that will address the following questions:

1) Is there a Higgs particle?

2) Is there supersymmetry (SUSY)?

3) What is dark matter?

4) Where has all the antimatter gone?

5) Why are there only six quarks?

More at press.web.cern.ch and scitech.

## Tuesday, September 09, 2008

### The LHC countdown is on!

LHC First Beam on

10 September 2008

On 10 September scientists at CERN in Geneva, Switzerland will attempt for the first time to circulate a beam in the Large Hadron Collider. The LHC is the world’s most powerful particle accelerator, and will produce beams seven times more energetic, and around 30 times more intense than any previous machine when it reaches design performance.

The first injection of a beam is scheduled for 9:30 CET (+9 hours from Pacific Standard Time), and will be preceded by a planning meeting that will be relayed to the Globe from 9:00.

The Live webcast can be found here.

## Friday, August 22, 2008

### Edward Witten for VP?

After years of work on a candidate theory of quantum gravity, there's word that the father of M-theory may well be Obama's future VP candidate. After all, it is a well-known fact that Witten was actively involved in former democratic presidential candidate George McGovern's campaign. Moreover, he has published articles in The New Republic and The Nation and has donated more than $50,000 in democratic campaign contributions from 2000-2008. Witten's desire for change clearly rivals that of any other VP hopeful. Not to mention, he's pretty darned smart. So, look out Chet Edwards and Joe Biden, your VP hopes are hanging by a string. ;)

## Thursday, July 31, 2008

### NASA Confirms Water on Mars

NASA scientists said on Thursday they had definitive proof that water exists on Mars after tests on ice found on the planet in June by the Phoenix Mars Lander.

Until now, the evidence for ice has been circumstantial. That was based on photos Phoenix took of a hard splotchy area near its landing site and changes it saw in a trench.

The robot heated up ice in one of its instruments earlier this week. Scientists say the chemical test confirms the presence of ice near the Martian north pole.

## Monday, July 28, 2008

### Tree Quantum Field Theory

Gurau et. al. posted a new paper today on arxiv (arxiv.org/0807.4122 [hep-th]), proposing a new approach to quantum field theory: marked trees.

We propose a new formalism for quantum field theory which is neither based on functional integrals, nor on Feynman graphs, but on marked trees. This formalism is constructive, i.e. it computes correlation functions through convergent rather than divergent expansions. It applies both to Fermionic and Bosonic theories. It is compatible with the renormalization group, and it allows to define non-perturbatively {\it differential} renormalization group equations. It accommodates any general stable polynomial Lagrangian. It can equally well treat noncommutative models or matrix models such as the Grosse-Wulkenhaar model. Perhaps most importantly it removes the space-time background from its central place in QFT, paving the way for a nonperturbative definition of field theory in noninteger dimension.

### SU(5) Grand Unified Model from Non-perturbative String Theory

Mirjam Cvetic and Timo Weigand posted a new paper today (arXiv:0807.3953v2 [hep-th]) on symmetry breaking and SU(5) GUT model building from supergravity/non-perturbative string theory. The abstract is as follows:

We propose a robust supergravity model of dynamical supersymmetry breaking and gauge mediation, and a natural embedding in non-perturbative string theory with D-branes. A chiral field (and its mirror) charged under "anomalous" U(1)'s acts as a Polonyi field whose hierarchical Polonyi-term can be generated by string instantons. Further quartic superpotential terms arise naturally as a tree-level decoupling effect of massive string states. A robust supersymmetry breaking minimum allows for gauge mediation with soft masses at the TeV scale, which we realise for a globally consistent SU(5) GUT model of Type I string theory, with a D1-instanton inducing the Polonyi term.

### Former Google Engineers Launch Cuil Search Engine

A former Google employee and her husband launched a new search engine Monday called Cuil (pronounced "cool", http://www.cuil.com), aiming to topple Google by indexing more Web pages than the search giant.

Cuil, of Menlo Park, California, is led by Anna Patterson , a former leader of Google's search index and her husband, Tom Costello, who researched and developed search engines at Stanford University and IBM. The two, president and CEO, respectively, met at Stanford.

Russell Power, the third cofounder of the group, also worked at Google on search indexing, Web rankings, and spam detection. He works as vice president of engineering at Cuil.

The company, which shaved an 'L' off its name to become Cuil, said it has indexed 120 billion Web pages and can provide results organized by ideas with complete privacy for users.

Google on Friday said it had discovered 1 trillion unique Web pages on the Internet, but did not give an updated number on how many of those pages it has indexed.

Cuil said its search engine goes beyond traditional approaches by analyzing the context of each page and the concepts behind each query so it can provide better rankings by content rather than popularity. Cuil then organizes similar results into groups and sorts them by category. It also offers tabs to clarify subjects, as well as suggestions on how to refine searches.

Cuil isn't the first Google rival to launch this year. Wikia Search, a highly anticipated search engine from Wikipedia founder Jimmy Wales, made its official debut in January . Wikia Search hopes to provide better search results by allowing a community of users to index pages by using their Web page rankings and other suggestions, as well as its own indexing of the Web.

InfoWorld

## Saturday, July 26, 2008

### The Dark Knight's Suit

In "The Dark Knight," Batman complains that he needs a better suit - and that's a concern for the real-life knights in the U.S. military as well. The Pentagon would love to have Wayne Enterprises' secret for lighter, more flexible body armor. Nanocomp Technologies based in New Hampshire, is among several companies working on carbon-nanotube composites for military applications.

"We're really focused on trying to create layers of protection that would improve things for our troops," Peter Antoinette, Nanocomp's president and chief executive officer, told me. "It would take a number of years before you could order up a suit, and then a billionaire would have to pay seven figures for a suit that would work the way they do in the movies."

As an initial step, Nanocomp is working on nanotubes for next-generation wiring in satellites and aircraft. Carbon nanotubes are highly conductive and could replace copper wire in settings where reducing weight is crucial. "We're less than one-tenth the weight of copper, so if you can take 1,000 pounds off these satellites or aircraft, you'd be saving a huge amount of money," Antoinette said.

Commercialization of nanotube wiring could begin as early as next year, Antoinette said. He added that Nanocomp's materials are already undergoing military testing, and body-armor applications could start emerging in 2010 or so.

Kakalios agreed that nanotubes are a technology to watch: "Compared to steel cables, it's about 100 times stronger. Whether you can make this in large enough quantities, in long enough length scales ... that work is still in progress."

### Northern Lights Explained

NASA released findings Thursday that indicate magnetic explosions about one-third of the way to the moon cause the northern lights, or aurora borealis, to dance across the sky in spectacular shapes and colors.

A fleet of five small satellites, called Themis, observed the beginning of a geomagnetic storm in February, while ground observatories recorded the brightening of the northern lights.

A team led by UCLA scientist Vassilis Angelopoulos confirmed that the observed storm about 80,000 miles from Earth was triggered by a phenomenon known as magnetic reconnection. Every so often, the Earth's magnetic field lines are stretched like rubber bands by solar energy, snap, are thrown back to Earth and reconnect, in effect creating a short circuit.

This stored-up energy powers the northern and southern lights, Angelopoulos said.

LA Times

## Friday, July 04, 2008

### Xian-Jin Li and an attempted Proof of the Riemann Hypothesis

A new paper by Xian-Jin Li was uploaded on arxiv this week, with a claimed "proof" of the Riemann Hypothesis. Well, a "proof" is actually given for E. Bombieri's refinement of A. Weil's positivity condition, which implies the Riemann Hypothesis. The "proof" is said to be in the spirit of Alain Connes' approach to the Riemann Hypothesis.

Fortunately, (or unfortunately) it didn't take too long for Fields medalists to punch holes in the purported proof. Alain Connes himself, as well as Terence Tao pointed out certain problems on pages 20 and 29.

Alain Connes politely states in his blog:

*I dont like to be too negative in my comments. Li's paper is an attempt to prove a variant of the global trace formula of my paper in Selecta. The "proof" is that of Theorem 7.3 page 29 in Li's paper, but I stopped reading it when I saw that he is extending the test function h from ideles to adeles by 0 outside ideles and then using Fourier transform (see page 31). This cannot work and ideles form a set of measure 0 inside adeles (unlike what happens when one only deals with finitely many places).*

While Terence Tao, adds:

*It unfortunately seems that the decomposition claimed in equation (6.9) on page 20 of that paper is, in fact, impossible; it would endow the function h (which is holding the arithmetical information about the primes) with an extremely strong dilation symmetry which it does not actually obey. It seems that the author was relying on this symmetry to make the adelic Fourier transform far more powerful than it really ought to be for this problem.*

Xian-Jin Li has since posted revisions of his paper, specifically making changes on page 20 and 29, where Connes and Tao pointed out difficulties. However, it is doubtful Connes and Tao will take another look at the new version of the paper.

## Sunday, April 06, 2008

### Extremal Black Holes & Elementary Particles (1995)

Witten and Seiberg found a way to eliminate certain singularities in a four-dimensional quantum field theory with supersymmetry--an extension of the standard model of particle physics that attempts to incorporate all the forces of nature except gravity. They did it by introducing to the theory a hypothetical particle called a magnetic monopole.

By gradually changing a particular parameter in the equations describing supersymmetry, the theorists could show that this monopole becomes massless right when the equations, in the absence of monopoles, point to infinity as the answer. This approach makes it possible to circumvent troubling singularities and obtain reasonable solutions to the equations.

Strominger asked himself whether miniature black holes carrying an electric charge might play a similar role in string theory. These curious objects are closely related to the black holes of relativity theory and astronomical speculation.

"Ordinary" astronomical black holes are generally characterized by their mass, electric charge, and angular momentum, or spin. In string theory, researchers deal with "extremal" black holes--tiny bodies with mass and charge comparable to those of elementary particles.

Strominger looked at what happens to such a black hole when one varies parameters determining the shapes of the curled-up, six-dimensional spaces that arise in string theory. He discovered that as the shape changes, the mass of a charged black hole dwindles to zero precisely when the singularities he was worried about would arise.

At first glance, the notion of a massless black hole may seem contradictory, but it arises naturally out of the mechanics of string theory. In some situations, a black hole's mass is proportional to its area. Making this area smaller and smaller eventually leads to a black hole with zero mass.

"It's a very special kind of black hole," Greene says. "But it's still sensible to think of it as being a black hole, because it evolved from a massive black hole."

The transformations studied by Strominger also revealed a direct correspondence between extremal black holes and strings. He could avoid the singularities normally encountered in the particular formulation of string theory he was using by treating black holes as strings and strings as black holes.

When Greene and Morrison heard about Strominger's work, they quickly realized there was no barrier to continuing a shape transformation beyond the massless black hole stage. In fact, this stage appeared to mark a transition not unlike that occurring when a solid melts or a liquid freezes.

In the case of water, for example, lowering the temperature turns the liquid to ice. Raising the temperature reverses the process. Although ice and liquid water look and behave differently, they merely represent two phases of the same molecular substance.

Something similar happens as the geometry of the six-dimensional components of string theory gradually changes. At a certain critical value of a shape parameter, one gets a phase transition in which tiny, charged black holes are transformed into strings in specific vibrational states. The vibrating strings, in turn, correspond to various elementary particles.

"When you follow the transition in detail, what appear to be black holes in the first phase--analogous to water--evolve into fundamental particles in the second phase--analogous to ice," Greene says. "That is, black holes reappear as more conventional elementary particles, such as electrons or quarks."

"What wasn't clear, but becomes obvious with this work, is that black holes and elementary particles are really one and the same thing as they smoothly change from one to another," he adds.

The researchers also noted that, at the same moment black holes transmute into elementary particle states, the topology, or basic geometric shape, of the accompanying six-dimensional space changes markedly. Such topological transformations can be as radical as changing a beach ball into a doughnut-shaped ring by ripping a hole in the plastic before reshaping the material into its new form.

Science News, August 26, 1995 by Ivars Peterson

## Tuesday, February 26, 2008

### SUSY Bet @ Burning Man

Here's a video I came across of some physics students and Garret Lisi talking SUSY physics at Burning Man, August 30, 2006. Apparently Garret is betting that SUSY particles will not be found at the LHC by 2010. Either way, I enjoy the physics discussion amidst the echoing electronic music. Perhaps Garret should schedule a quantum gravity mini-seminar at Burning Man 2010 and invite physics and math PhD students from around the world!

## Wednesday, January 16, 2008

### Antimatter from X-ray binary stars

In 1978, gamma ray detectors flown on balloons detected a type of gamma ray emerging from space that is known to be emitted when electrons collide with positrons — meaning there was antimatter in space.

"It was quite a surprise back then to discover part of the universe was made of antimatter," researcher Gerry Skinner, an astrophysicist at Goddard Space Flight Center in Greenbelt, Md., told SPACE.com.

These gamma rays apparently came from a cloud of antimatter roughly 10,000 light-years across surrounding our galaxy's core. This giant cloud shines brightly with gamma rays, with about the energy of 10,000 suns.

What exactly generated the antimatter was a mystery for the following decades. Suspects have included everything from exploding stars to dark matter.

Now, an international research team looking over four years of data from the European Space Agency's International Gamma Ray Astrophysics Laboratory (INTEGRAL) satellite has pinpointed the apparent culprits. Their new findings suggest these positrons originate mainly from stars getting devoured by black holes and neutron stars.

The researchers calculate that a relatively ordinary star getting torn apart by a black hole or neutron star orbiting around it — a so-called "low mass X-ray binary" — could spew on the order of one hundred thousand billion billion billion billion positrons (a 1 followed by 41 zeroes) per second. These could account for a great deal of the antimatter that scientists have inferred, reducing or potentially eliminating the need for exotic explanations such as ones involving dark matter.

"Simple estimates suggest that about half and possibly all the antimatter is coming from X-ray binaries," said researcher Georg Weidenspointner of the Max Planck Institute for Extraterrestrial Physics in Germany.

Now that they have witnessed the death of antimatter, the scientists hope to see its birth.

"It would be interesting if black holes produced more matter than neutron stars, or vice versa, although it's too early to say one way or the other right now," Skinner explained. "It can be surprisingly hard to tell the difference between an X-ray binaries that hold black holes and neutron stars."