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Theory Seminar
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 Theory Seminars Spring 2011 View Printable Version

## Tentative Schedule

### January 24

Abstract:

A recent progress on construction of a massive extension of General Relativity,
and its cosmological consequences  will be discussed

### January 31

Speaker: Shin’ichiro Ando, Caltech

Abstract:

High-energy gamma rays keep revealing new aspects of the Universe, thanks to the current telescopes such as Fermi, HESS, MAGIC, VERITAS, etc.

One of the important goals for these telescopes is to study the nature of dark matter, by looking for annihilation gamma rays.  Because dark matter is annihilating everywhere in the Universe, the diffuse gamma-ray background will contain some information on dark matter.  In this talk, I introduce a new analysis method of the gamma-ray background, by using the angular power spectrum.  This way, one can efficiently analyze spatial distributions of photons, and since dark matter annihilation follows density in a different way from other astrophysical sources, the angular power spectrum is also characteristic and distinguishable.  The dark matter can be identified in the angular power spectrum with Fermi if its contribution is ~10% or more.

Another important physics that one can learn with gamma rays is magnetic fields in intergalactic space.  This is because distribution of secondary photons from electromagnetic cascades is affected by magnetic fields.  We therefore analyzed stacked AGN images from Fermi data, and found an anomalous excess compared with point-spread function.  If this is due to intergalactic magnetic fields, then the field value will be around 1 femto-Gauss.

### February 7

Speaker: Kai Wang, Institute for the Physics and Mathematics of the Universe, University of Tokyo

Abstract:

CDF collaboration has recently published various updated measurements on top quark forward-backward asymmetry in 1101.0034. The measured total asymmetry is significantly larger than the SM prediction from QCD NLO calculation. In this talk, I will try to give a comprehensive theory review on the Beyond Standard Model proposals to this anomaly, discussing their features, potential problems as well as their immediate predictions at the LHC.

### February 11

Speaker:  Mark Strikman, Penn State University

** Special seminar at 10:30 AM in 705 Pupin **

### February 14

Speaker: Ira Rothstein, Carnegie Mellon University

Abstract:

The scattering lengths of ultra-cold atoms can be tuned to be arbitrarily large leading to strongly interacting many body systems. What makes these systems particularly compelling is that at infinite scattering length they manifest Schrodinger symmetry, which is the non-relativistic analogue of conformal symmetry. As such, many field theoretic techniques which previously had no physical applications can now be tested in the laboratory. In this talk I will discuss how one can use the operator product expansion in conjunction with dispersion relations to generate sum rules for dynamical response functions in a first principles systematic fashion.

### February 21

Speaker: Guy Moore, McGill University

Abstract:

Hydrodynamics is the universal theory describing the behavior of fluids when their space time variation is on scales longer than any microphysical scale in the fluid. Relativistic hydro has applications in heavy ion collisions and early Universe cosmology, and has seen a surge of interest due to heavy ion experiments and theoretical developments in AdS/CFT. I will explain what second order hydrodynamicsis and why it is the minimum theory to study in the relativistic case.Then I discuss some limitations of the theory, including a new bound on how small the viscosity can be and a complication in the rigorous definition of the viscous relaxation time $\tau_\pi$.

### February 28

Speaker:  Dimitrios Giannios, Princeton University

Abstract:

Collimated, relativistic outflows have been observed or inferred to originate from supermassive black holes in the centers of galaxies, solar-mass compact objects in binaries and gamma-ray bursts. A theoretical paradigm for jet formation has been developed since the late 1970s that can account in a unifying manner for all these sources. This paradigm envisions that jets come from rotating objects (neutron stars, black-hole ergospheres, or accretion disks) with strong magnetic fields that extract their rotational energy. Despite recent progress in the field, we still lack a coherent connection between the jet dynamics and the electromagnetic radiation emitted by these sources. The guiding theme that I propose for such a connection is the dissipation of magnetic energy in the jet. This key process connects the aspects of acceleration of jets, their interaction with the external medium, and radiation mechanisms.

### March 3

Speaker: Yuri Dokshitzer, CNRS - Paris VI

** Special seminar at  2:10 PM in 705 Pupin **

### March 7

Speaker: Lee Smolin, Perimeter Institute

Abstract:

We propose a deepening of the relativity principle according to which the invariant arena for non-quantum physics is a phase space rather than spacetime. Descriptions of particles propagating and interacting in spacetimes are constructed by observers, but different observers, separated from each other by translations, construct different spacetime projections from the invariant phase space. Nonetheless, all observers agree that interactions are local in the spacetime coordinates constructed by observers local to them. This framework, in which absolute locality is replaced by relative locality, results from deforming momentum space, just as the passage from absolute to relative simultaneity results from deforming the linear addition of velocities. Different aspects of momentum space geometry, such as its curvature, torsion and non-metricity, are reflected in different kinds of deformations of the energy-momentum conservation laws. These are in principle all measurable by appropriate experiments. We also discuss a natural set of physical hypotheses which singles out the cases of momentum space with a metric compatible connection and constant curvature.

### March 28

Speaker: Diego Trancanelli, University of Wisconsin

Abstract:

In this talk we set up a study of the processes of black hole formation and thermalization using the gauge/gravity correspondence. Our analysis is in the context of a matrix quantum mechanics, the so-called plane-wave (or BMN) matrix model. We consider configurations of the model that correspond to the scattering of "fuzzy spheres" and derive the spectrum of fluctuations around these configurations. We find that when two fuzzy spheres intersect, classical tachyons can form at the intersection locus. We follow the time evolution of these modes (also using numerical simulations) and speculate on their role toward the possible thermalization of the system.

### April 4

Speaker: Jessie Shelton, Yale University

Abstract:

The anomalously large top forward-backward asymmetry measured at the Tevatron is a striking result which, if borne out, requires new physics at relatively low mass scales.  Whatever this new physics may be, it must carry some nontrivial flavor structure, and thus provides a first hint for beyond-the-standard-model theories of flavor. I'll talk about a model which connects the observed top forward-backward anomaly to anomalies in B mesons, and discuss the discovery prospects for this and other models at the LHC.  I will further discuss prospects for measuring the top forward-backward asymmetry at the LHC.

### April 11

Speaker: Matthew Kleban, New York University

Abstract:

I will describe a class of time-dependent solutions in string- or M-theory that are exact with respect to alpha-prime and curvature corrections and interpolate in physical space between regions in which the low energy physics is well-approximated by different string theories and string compactifications. The regions are connected by expanding "domain walls" but are not separated by causal horizons, and physical excitations can propagate between them. Examples include solutions that interpolate between oriented and unoriented string theories, and also between type II and heterotic theories. These solutions can be weakly curved and under perturbative control everywhere and can asymptote to supersymmetric at late times.

### April 18

Speaker: Henri Kowalski, DESY, Hamburg

Abstract:

In the talk I will show that  HERA data can be described by a universal gluon density which can be identified  with a pomeron. The new precise data on F2 allow to determine the properties of a Discrete-Pomeron solution to the BFKL equation. The DP structure is strikingly similar to the closed-string, hard wall pomeron in ADS/CFT.

** Special Particle-Nuclear/ Theory seminar at  2:10 PM in 831 Pupin **

### April 25

Speaker: Sean Hartnoll, Stanford University

Abstract:

This talk will be an overview of recently developed holographic approaches to strongly interacting condensed matter systems. I will explain why certain theoretical and experimental challenges in unconventional materials may be amenable to a holographic approach. From a theoretical perspective I will argue that holography provides new computationally controlled entry points into non-Fermi liquid phases and the emergence of superconductivity from such phases. I will also argue that holography makes explicit the natural observables of strongly correlated media that suggest novel emphases for theoretical and experimental studies. I will not assume any previous knowledge of holography.

### May 16

Speaker: Arthur Kosowsky, University of Pittsburgh

Abstract:

Peculiar velocities of galaxies and galaxy clusters contain a significant amount of information about the growth of structure and the expansion history of the universe. Future experiments promise to mine this information, through the Sunyaev-Zeldovich effect with galaxy clusters and with large catalogs of type-1a supernova which can be used as standard candles. I will discuss the extent to which these data sources may provide future constraints on dark energy and modified gravity. In particular, the mean pairwise velocitystatistic is especially promising because it likely is much less sensitive to systematic errors than most other contemplated dark energy probes.