Pruhdvi Battiprolu (UM): Criteria for discovery and exclusion of new physics and its application to proton decay searches | 1/14/2022
The projected discovery and exclusion capabilities of particle physics and astrophysics/cosmology experiments are often quantified using the median expected p-value or its corresponding significance. We argue that this criterion leads to flawed results, which for example can counterintuitively project lessened sensitivities if the experiment takes more data or reduces its background. We advocate for standard use of the “exact Asimov significance” detailed in this talk. We then consider a modified frequentist approach, which for exclusion case is known as the CLs technique, for projecting sensitivities, and contrast it with the standard frequentist approach among others. And, as an application of some of these techniques, we study the statistical significance of proton decay at the current and future neutrino detectors. We first review some statistical methods that are employed in various proton decay sensitivity studies, and along the way we estimate the current lower limit on proton partial lifetimes at various confidence levels based on Super-Kamiokande’s data. We present our projections for proton partial lifetime in p → ν K+ and p → e+ π0 decay channels at DUNE, JUNO, and Hyper-Kamiokande.
Arash Arabi Ardehali (Stonybrook): Root-of-unity asymptotics of the 4d superconformal index and AdS/CFT | 1/21/2022
It has been recently understood that BPS AdS5 black holes are encoded in a certain partition function (known as the 4d superconformal index) of the N=4 super-Yang-Mills, in the limit where the "complexified temperature" approaches 2\pi i. In this seminar we discuss limits where the complexified temperature approaches rational multiples of 2\pi i (hence the associated fugacity nears a root of unity). We will find infinitely-many saddles different from the black holes, and discuss the analogy with the better-known AdS3/CFT2 setting where also infinitely-many saddles arise in a so-called Farey Tail expansion of the 2d superconformal index.
Susanne Reffert (University of Bern) : The Large Charge Expansion | 2/4/2022
Over the last few years, it has become clear that working in sectors of large global charge leads to significant simplifications when studying strongly coupled CFTs, theories which are otherwise often inaccessible to analytic methods. It allows us in particular to calculate the CFT data as an expansion in inverse powers of the large charge.
In this talk, I will introduce the large-charge expansion via the simple example of the O(2) model and will then apply it to a number of other systems which display a richer structure, such as those with non-Abelian global symmetry groups. Using large-N methods in conjunction with large charge gives us even more control over the dynamics and lets us study the system away from the conformal point.
Mikhail Solon (UCLA) : Quantum Field Theory Tools for Gravitational Wave Science | 2/11/2022
Future gravitational wave detectors will map out and characterize every binary merger in the history of the universe. The possibilities for new and unexpected scientific discoveries from this wealth of data is staggering, but hinges crucially on complementary advances in our theoretical understanding of the nature of gravitational wave sources. However, the path from Einstein’s equation to precision binary dynamics is notoriously difficult, and conventional methods may not scale to the demands of future detectors. I will describe our recent efforts in solving the relativistic two-body problem using modern tools from quantum field theory.
Masanori Hanada (University of Surrey) : Entanglement between matrix degrees of freedom and gauge theory counterpart of entanglement island | 2/18/2022
In gauge/gravity duality, matrix degrees of freedom on the gauge theory side play important roles for the emergent geometry. In this talk, we discuss how the entanglement on the gravity side can be described as the entanglement between matrix degrees of freedom. Our approach, which we call "matrix entanglement", is different from "target-space entanglement" proposed and discussed recently by several groups. The examples studied include a small black hole in AdS5*S5 that can evaporate without being attached to a heat bath, for which our approach suggests a gauge theory counterpart of the entanglement island behind the horizon. Specifically, we propose that the confined degrees of freedom in the partially-deconfined states correspond to the island. Intuitively, the confined sector consists of D-branes sitting behind the horizon and sourcing the exterior geometry.
Mark Van Raamsdonk (UBC) : Cosmology from vacuum physics | 2/25/2022
We discuss a holographic approach to describing cosmological physics. The cosmological spacetime is encoded in a special state of a four-dimensional quantum field theory that is not conventionally holographic. The state is produced via a Euclidean path integral that includes a three-dimensional holographic theory at a boundary in the Euclidean past. The same Euclidean path integral can be used to define a dual static spacetime, and the many of the observables in the cosmology are equivalent to vacuum observables in the static spacetime. This duality has interesting consequences, for example it gives a simple explanation for correlations between regions of the universe that apparently were never in causal contact. The model gives an effective field theory whose fundamental constant that is negative, but generically will have a phase of accelerated expansion via a rolling scalar.
Ibrahima Bah (Johns Hopkins) : Topological solitons in gravity | 3/18/2022
In this talk I will discuss aspects of microscopic degrees of freedom of gravity as motivated by string theory. Although these are expected to be generically quantum mechanical, our goal is to understand a class of such states that are coherent enough to admit classical descriptions in Einstein gravity. The construction of such states corresponds to adding interesting topological structures in spacetime with the help of compact extra dimensions. The constructions manifestly behave like ultra compact objects, dubbed topological stars, which can also model black hole microstates. I will discuss physical aspects of such constructions.
Masha Baryakhtar (University of Washington) : Black Hole Searches for Ultralight Bosons | 3/25/2022
Theories that seek to explain the outstanding puzzles of the Standard Model of particle physics often predict new, light, feebly-interacting particles whose discovery requires novel search strategies. These include light spin-0 axions and spin-1 dark photons. I will discuss how rotating black holes source clouds of exponentially large numbers of gravitationally-bound particles and so create nature's laboratories for ultralight bosons. This process causes black holes to spin down and the bound bosons emit gravitational waves, allowing observatories such as LIGO and Virgo to search for new particles. For a new dark photon particle that couples to the Standard Model, the systems could undergo dramatic electromagnetic cascades and appear as novel pulsar-like objects in the sky.
Neal Weiner (NYU) : A Step in Understanding the Hubble Tension | 4/1/2022
Precision cosmology has now allowed us to study whether the simple LCDM model agrees with data. Interestingly, a tension has arisen between measurements of the Hubble Parameter - how fast the universe is expanding - from the recent universe compared with values extracted from the early universe. I will discuss this tension and some ideas of how to address it requiring physics beyond LCDM. In particular, I will discuss models with a light (~eV) mass threshold as a means to address the tension and the possibility of testing these ideas in the future.
Tracy Slatyer (MIT) : Thermal Squeezeout for Strongly Interacting Dark Matter | 4/8/2022
I will discuss the potential importance of a dark-sector phase transition in the early universe in setting the measured relic abundance, for a simple scenario with strongly interacting dark matter. Enhancement of the dark matter density within shrinking pockets of the high-temperature phase leads to a dramatic reduction in the late-time dark matter abundance, allowing for much heavier dark matter than in the standard thermal freezeout scenario. I will show new results on a class of specific models realizing this scenario, including experimental constraints and the effects of entropy injection from decay of metastable dark-sector particles.
JJ Carrasco (Northwestern) : Color-Dual Effective Field Theory | 4/15/2022
The duality between color and kinematics, and associated double copy construction has allowed some of the sharpest perturbative calculations in both supergravity theories and classical invariant observables relevant to next generation gravitational wave physics. I will talk about ways related insights can be applied to understanding the behavior of EFT operators in gauge and gravity theories. Pairs of color-dual numerators can be composed to generate new color-dual numerators. This presents an opportunity to efficiently climb to amplitudes of arbitrarily high mass dimension --- without resorting to ever more expensive Ansätze --- thereby spanning the tower of double-copy consistent gauge and gravity operators with a small number of building blocks. I will apply this technology towards discovering some hints about the color-dual fate of N=4 supergravity.
