Organizer: Henriette Elvang
| Date |
Speaker |
Title |
Abstract |
| Sep 6 |
Malcolm Perry
(Cambridge) |
Generalized Geometry of String and M-theory
|
The spacetimes that provide backgrounds for string and for M-theory have hidden symmetries when compactified on a d-dimensional flat torus. These are variously the S,T or U-dualities and are controlled by Od,d for string theory and the exceptional groups Ed for M-theory in the cases d = 4, 5, 6, 7 or 8. Generalised geometry is a description of the backgrounds if there are no compactification onto a torus. We will describe the generalised geometry for these simple cases and then move on to how one can see generalised geometry arises from the E11 construction. The construction shows how dualities can be made manifest as symmetries of the theory even in the absence of symmetries of the background or compactification. We will end with some observations about how one can construct gauged versions of the theory and on the quantised string and M 2-branes. |
| Sep 13 |
Bibhushan Shakya
(Michigan) |
How I learned to Worry about Stops and Love Naturalness: topics in Lambda-SUSY
|
|
Sep 20
|
Tanja Rindler-Daller
(Michigan) |
Cosmological Constraints on Scalar-Field Dark Matter
|
Despite the great successes of the Cold Dark Matter (CDM) model in explaining a wide range of observations of the global evolution and the formation of galaxies and large-scale structure in the Universe, the origin and microscopic nature of dark matter is still unknown. The most common form of CDM considered to-date is that of Weakly Interacting Massive Particles (WIMPs), but, so far, attempts to detect WIMPs directly or indirectly have not yet succeeded, and the allowed range of particle parameters has been significantly restricted. Some of the cosmological predictions for this kind of CDM are even in apparent conflict with observations (e.g. cuspy/cored halos and the predicted overabundance of satellite dwarf galaxies). For these reasons, it is important to consider the consequences of different forms of CDM. We focus here on the hypothesis that the dark matter is comprised, instead, of ultralight bosons that form a Bose-Einstein Condensate (BEC), described by a complex scalar field. We start from the Klein-Gordon and Einstein field equations to describe the evolution of the Friedmann-Robertson-Walker (FRW) universe in the presence of this kind of
dark matter. We find that, in addition to the phases of radiation-domination, matter-domination and Lambda-domination familiar from the standard "LambdaCDM" model, there is an earlier phase of "scalar-field"-domination, which is special to our model. In addition, while WIMP CDM is non-relativistic at all times after it decouples, the equation of state of BEC scalar field dark matter (SFDM) is found to be relativistic at early times, evolving from stiff to radiation-like, before it becomes non-relativistic and CDM-like at late times. The timing of the transitions between these phases and regimes is shown to yield fundamental constraints on the SFDM model parameters, particle mass and self-interaction coupling strength. We show that SFDM is compatible with observations of the evolving background universe, by deriving the range of particle parameters required to match observations of the cosmic microwave background (CMB) and the abundances of the light elements produced by Big Bang nucleosynthesis (BBN), including N_eff, the effective number of neutrino species, and the epoch of matter-radiation equality z_eq. Indeed, our model can accomodate current observations in which N_eff is higher at the BBN epoch than at z_eq, probed by the CMB, which is otherwise unexplained by the standard CDM model involving WIMPs. We also show that SFDM without self-interaction (also called ‘Fuzzy Dark Matter’) is not able to comply with the current constraints from BBN, and can therefore be ruled out. |
| Oct 4 |
Finn Larsen
(Michigan) |
Introduction to topics of the MCTP black hole workshop
|
Black holes in string theory offer an arena for profound and fundamental questions in theoretical physics that continues to inspire new and fruitful avenues of research. Challenging foundational questions in quantum gravity are being elucidated by the impressive progress on precision counting of black hole microstates. At the same time researchers in the field are being humbled by the ever sharper confusions posed by the black hole information paradox. The MCTP workshop on black holes in string theory will bring together about 30 active researchers in the area with roughly equal proportion of senior and junior workers. The format will encourage informal discussions over formal lectures in order to promote the exchange of ideas and encourage new collaborations. In order to be maximally productive the workshop will primarily focus on "fundamental" issues at the expense of the exciting interdisciplinary developments involving "applications" to condensed matter, QCD matter, and other strongly coupled systems. Nevertheless these frontiers will of course inform the discussion. |
| Oct 25 |
Annika Peter
(Ohio State) |
Snuffing Out Dark Matter
|
How will we recognize dark matter when we see it? And what kinds of particle properties may it have? In this talk, I will discuss two aspects of finding and characterizing dark matter. First, I will discuss a new signal for WIMP dark matter: gravitational focusing in direct-detection experiments. This effect leads to an energy-dependent phase-shift in the peak direct-detection event rate throughout the year. I will discuss this in light of current putative annual-modulation claims. Second, I will talk about strong dark-matter self-interactions and astronomical observations. I will show that large cross sections may be lurking, and how different types of self-interactions lead to different dark-matter interpretations of observations of matter distributions in the sky. |
| Nov 15 |
Leonardo Rastelli
(Stony Brook / YIPT) |
The Superconformal Bootstrap Program
|
I will outline the modern bootstrap program for four-dimensional theories with extended superconformal symmetry. The bootstrap equations neatly split into two classes. There are ``minibootstrap'' equations for supersymmetric quantities, which can be solved analytically, and full-fledged bootstrap equations for non-protected quantities, which can be studied numerically. The entire program relies on general symmetry principles, with no need for ``fields'' or Lagrangians. After a general introduction, I will mostly focus on the numerical results of the N = 4 bootstrap, and on their interpretation in N = 4 super Yang-Mills theory. |
| Nov 22 |
Joe Minahan
(Uppsala) |
Three-point functions for short operators at strong coupling
|
Using the AdS/CFT correspondence we compute the three-point structure constants for primary operators in planar N=4 super Yang-Mills at strong coupling. The computation involves finding the relevant vertex operators for the massive string states dual to the operators and then computing their three-point string amplitudes. |
| Dec 6 |
Peter Graham
(Stanford) |
Axion detection with NMR
|
The axion is a well-motivated dark matter candidate, but is challenging to search for. We propose a new way to search for QCD axion and axion-like-particle (ALP) dark matter. Nuclei that are interacting with the background axion dark matter acquire time-varying CP-odd nuclear moments such as an electric dipole moment. In analogy with nuclear magnetic resonance, these moments cause precession ofnuclear spins in a material sample in the presence of a background electric field. This precession can be detected through high-precision magnetometry. With current techniques, this experiment has sensitivity to axion masses below 10^-9 eV, corresponding to theoretically well-motivated axion decay constants around the grand unification and Planck scales. With improved magnetometry, this experiment could ultimately cover the entire range of masses below 10^-6 eV, just beyond the region accessible to current axion searches. A discovery in such an experiment would not only reveal the nature of dark matter and confirm the axion as the solution of the strong CP problem, but would also provide a glimpse of physics at the highest energy scales, far beyond what can be directly probed in the laboratory. |
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