RESEARCH TALKS

Emil AKHMEDOV

Isometry invariance of exact correlation functions in various charts of Minkowski and de Sitter spaces

Abstract

We consider quantum field theory with self-interactions in various patches of Minkowski and de Sitter spacetimes. Namely, in Minkowski spacetime we consider separately the right (left) Rindler wedge, past wedge, and future wedge. In de Sitter spacetime we consider expanding the Poincaré patch, the static patch, the contracting Poincaré patch, and the global de Sitter itself. In all cases we restrict our considerations to the isometry invariant states leading to maximally analytic propagators. We prove that loop corrections in the right (left) Rindler wedge, in the past wedge (of Minkowski spacetime), in the static patch and in the expanding Poincaré patch (of de Sitter spacetime) respect the isometries of the corresponding symmetric spacetimes. All these facts are related to the causality and analyticity properties of the propagators for the states that we consider. At the same time in the future wedge, in the contracting Poincaré patch and in the global de Sitter spacetime infrared effects violate the isometries.

Jan AMBJORN

Are we bombarded by baby universes?

Abstract

It is suggested that the late time exponential expansion of our Universe is caused by the universe being bombarded by baby universes. This leads to a modified Friedmann equation that is in agreement with late-time cosmological observations without invoking a cosmological constant.

Arup BOSE

Limiting spectral distribution of random matrices with independent entries

Abstract

It is well known that the limit eigenvalue distribution of the scaled standard Wigner matrix is the semi-circular distribution whose $2k$th moment equals the number of non-crossing pair-partitions of $\{1,2,\ldots ,2k\}$. There are several extensions of this result in the literature, including the sparse case. We discuss extension of these results by relaxing significantly the i.i.d. assumption.
The limiting spectral distribution then involve a larger class of partitions. In the process we show how some new sets of partitions gain importance. Several existing and new results for their band and sparse versions, as well as for matrices with continuous and discretevariance profile follow as special cases.
Patterned random matrices such as the reverse circulant, the symmetric circulant, the Toeplitz and the Hankel matrices and their almost sure limiting spectral distribution (LSD), have also been studied quite extensively. Under the assumption that the entries are taken from an i.i.d. sequence with finite variance, the LSD are tied together by a common thread \textemdash{}the $2k$th moment of the limit equals a weighted sum over different types of pair-partitions of the set $\{1,2,\ldots ,2k\}$ and are universal. Some results are also known for the sparse case. Time permitting we show suitable extension of these results also, along the lines of the Wigner matrix

Daniel CARNEY

Comments on graviton detection

Abstract

To be communicated.

James CLINE

Phantom fluid cosmology

Abstract

Phantom fields have been widely invoked as a source of dark energy in cosmology, but rarely taken seriously as quantum theories. The vacuum is automatically unstable to production of negative energy ghost particles plus ordinary particles, requiring such theories to be effective only, below some UV cutoff. I will present recent cosmological constraints arising from the vacuum instability, both at the level of the homogeneous background, and the density perturbations.

Keshav DASGUPTA

De Sitter space as a Glauber-Sudarshan state

Abstract

In this talk I will discuss how a four-dimensional de Sitter space may be constructed as a Glauber-Sudarshan state, i.e as a coherent state, in type IIB string theory.

Maria Cristina DIAMANTINI

Superinsulators: the discovery of electric confinement in condensed matter systems

Abstract

Superinsulators are a new state of matter, which we predicted, and which has been experimentally observed on the insulating side of the superconductor-insulator transition in superconducting films. They are the S-dual of superconductors, with infinite resistance below a critical temperature. In the superinsulating state, Cooper pairs and Cooper holes are confined into neutral electric pions by electric strings, with the Cooper pairs playing the role of quarks. The underlying mechanism of superinsulation is, thus, Polyakov’s linear confinement of Cooper pairs anti-Copper pairs via instantons in 2d and monopoles in 3d. We present direct experimental evidences of this confining mechanism realised in thin superconducting films.

Gianluca GRIGNANI

Binary black hole mergers in the strong gravity background of a Kerr black hole

Abstract

The dynamics of a binary system moving in the background of a supermassive black hole is affected by tidal forces. For the Kerr black hole, I will derive in full generality the electric and magnetic tidal moments at quadrupole order. I will then make use of these moments in the scenario of a hierarchical triple system made of a Kerr black hole and a binary black hole system. I will describe how the secular dynamics of the binary system is distorted by the presence of tidal forces from a much larger Kerr black hole. The treatment includes strong gravitational effects beyond the post-Newtonian approximation for the tidal forces since the binary system is allowed to be close to the event horizon of the Kerr black hole. I will discuss how tidal forces affect the eccentricity of the binary system and its merger time.

Charlotte KRISTJANSEN

Integrable holographic dCFTs

Abstract

We discuss a class of integrable holographic defect conformal field theories where the defect is generated by a brane intersection, and can be described as a boundary state in the form of a matrix product state. Integrable defects include domain walls and monopoles.

Edwin LANGMANN

Elliptic Calogero-Sutherland model and quantum field theory

Abstract

In a project with Gordon Semenoff on QCD in 1+1 dimensions many years ago (when he was my postdoc advisor), we stumbled over a method to solve Calogero-Moser-Sutherland models using gauge theories (I did not know these models at the time). Since then, these models have reappeared in different forms in many of my research projects. I plan to describe a recent such project where a second quantization of the elliptic Calogero-Sutherland model led us to a new soliton equation and a non-relativistic variant of the Coleman correspondence. (Work with Bjorn Berntson and Jonatan Lenells.)

Bum-Hoon LEE

Gravity theory with the Gauss-Bonnet term

Abstract

Einstein gravity action has been describing cosmology and other phenomena quite successfully while it consists of the quite simple leading term. Recent observation data available through precise measurements suggests possibility to challenge the standard cosmology model. Among the possible candidate theories beyond the Einstein gravity theory, we will focus on the Gauss-Bonnet term, which is one of the simplest extension with the higher curvature. The properties of this theory will be explained by looking at the Black Holes, which show some characteristic differences compared with those of the Einstein gravity. We also mention the implication to the cosmology.

Taejin LEE

Four-graviton scattering and string path integral

Abstract

We evaluate the four-closed-string scattering amplitude, using the Polyakov string path integral in the proper-time gauge. By identifying the Fock space representation of the four-closed-string-vertex, we obtain a field theoretic expression of the closed string scattering amplitudes. In the zero-slope limit, the four-closed-string scattering amplitude reduces to the four-graviton-scattering amplitude of Einstein’s gravity. However, at a finite slope, the four-graviton scattering amplitude in the proper-time gauge differs not only from that of Einstein gravity, but also significantly differs from the conventional one obtained by using the vertex operator technique in string theory.

David LONDON

Anomalies in hadronic B decays

Abstract

At the present time, there are measurements of a number of observables in processes described by the quark-level transitions b –> s µ+ µ- and b –> c τ νbar_τ that disagree with the predictions of the standard model. A great deal of work has gone into exploring the new-physics (NP) explanations of these semileptonic B anomalies. Now, there are also discrepancies involving hadronic B decays, but because QCD is involved, much less attention has been paid to these hadronic B anomalies. Still, on quite general grounds, one expects that, if NP is present, it will affect both types of B decays. My group is looking into NP connections between the semileptonic and hadronic B anomalies. This is work in progress, and I will present a status report.

Richard MacKENZIE

Edge states and their cousins in an open SSH model

Abstract

The Su-Schrieffer-Heeger model is perhaps the simplest model with edge stages, states that are an essential aspect of materials known as topological insulators. In this talk, I will briefly describe the SSH model and will discuss edge states in a finite SSH chain in isolation and a chain with leads attached to the ends. The effect of the leads on the details of the states and in particular on the energy spectrum will be discussed.

Yuri MAKEENKO

Strings from Nambu-Goto to Polyakov and back

Abstract

I consider string anomalies which emerge from higher terms of the DeWitt