# Special Seminars & Colloquia

**FTPI occasionally hosts special seminars and colloquium when we have a visitor whose talk does not fit into existing seminar schedules. Please see the calendar below for our upcoming seminars.**

Our full catalogue of recordings is available on FTPI's YouTube Channel @FineTheoryInstitute

### Alexander Turbiner (Autonomous University of Mexico City)

**Quantum Anharmonic Oscillator: Almost Analytic Solution**

*For quartic anharmonic oscillator and double well potential matching the perturbation theory at small distances and semiclassical expansion at large distances locally accurate expressions (~10^-6 in relative deviation) for eigenfunctions are constructed for any coupling constant. These expressions lead to extremely accurate energies: 10^-9 - 10^-10 in relative deviations.*

## 2023

### Kaoru Hagiwara (KEK)

**CP Violating top-Higgs Coupling in SMEFT**

*The total cross section of the process mu- mu+ (greater than) vm vm~ ttH has strong dependence on the CP phase (xi) of the top Yukawa coupling, where the ratio of xi=pi and xi=0 (SM) grows to 630 at rts=30 TeV, 3300 at 100 TeV. We study the cause of the strong energy dependence and identied its origin as the (E/mW)2 growth of the weak boson fusion sub-amplitudes, WL- WL+ (greater than) ttH, when the two W's are longitudinally polarized. We repeat the study in the SMEFT framework where the EW gauge invariance is manifest, and find that the highest energy cross section is reduced to a quarter of the complex top Yukawa model result, with the same energy power. By applying the Goldstone boson (GB) equivalence theorem, we identied the origin of this strong energy growth of the SMEFT amplitudes as the contact dimension-6 pi-pi+ttH vertex, where pi^+- denotes the GB of W^+-. We obtain the Unitarity bound on the coecient of the SMEFT operator by using the optical theorem.*

### Francis Halzen (University of Wisconsin, Madison)

**ICECUBE: High-energy Cosmic Neutrinos and their First Sources**

### Junwu Huang (Perimeter Institute)

**A New Pulsar**

*Many extensions of the Standard Model predict the presence of ultra-light bosons in the low energy theory. If any of these bosons are in the mass range of 10⁻²⁰ to 10⁻¹⁰ eV they will affect the evolution of astrophysical black holes through the superradiance process. When a boson’s Compton wavelength is comparable to the size of a black hole, the boson binds to the black hole forming a gravitational atom in the sky. The occupation number of atomic states can grow exponentially to as large as 10⁷⁶, extracting energy and angular momentum from the black hole. **In this talk, I will present the first study of the electromagnetic signals coming from a black-hole superradiance cloud of a light dark photon. I will show how this dark photon superradiance cloud produces and hosts a rotating plasma of Standard Model charged particles. Crudely, this rotating plasma behaves like an electric dipole rotating around the black-hole spin direction. Just like a pulsar, which is qualitatively a rotating magnetic dipole, our system of a rotating electric dipole also produces extremely powerful, and potentially periodic, electromagnetic radiation. I will discuss the similarities and differences between our system and a pulsar, and several search strategies based on detailed numerical simulations.*

### Tao Han (University of Pittsburgh)

**EW Physics at Very High Energies: A Multi-TeV Muon Collider as a Case Study**

*The Standard Model electroweak (EW) sector exhibits some novel features at very high energies. At energies much larger than the EW scale, the EW gauge symmetry is essentially restored and the massless splitting phenomena dominate the EW physics. Beyond the familiar gauge theory splitting functions, we discuss the emergence of additional ``ultra-collinear'' splitting phenomena and the naive violation of the Goldstone-boson Equivalence Theorem. Because the SU(2) quantum numbers are explicit and observable in common physical processes, subtitles of the Bloch-Nordsieck theorem violation are discussed. The vector-boson fusion processes take over as the leading contributions at high energies, and the EW parton distribution functions are formulated. We implement the EW showering and illustrate its importance by calculating a number of physical processes at high energies within and beyond the SM. Finally, we take a multi-TeV muon collider as a case study for precision Higgs physics and for discovery at the new energy frontier.*

### Robert McGehee (University of Michigan)

**Directly Detecting Light Dark Matter**

*While the experimental program to detect ever lighter dark matter is proceeding full steam ahead, the theory of such light, detectable dark matter is at a crossroads. I will detail two examples of sub-GeV hadrophilic dark matter models which these future direct detection endeavors may discover while highlighting the serious challenges model builders face. The first achieves probe-able direct detection cross sections by way of a late-time, dark-sector phase transition, while the second does so by assuming the entire thermal bath is reheated at very low temperatures. Both models lead to dark matter-nucleon scattering cross sections of interest for near-future experiments for dark matter masses in the range of 100 keV-100 MeV, often in parts of parameter space with few or no model.*

## 2022

### Nadav Outmezguine (Lawrence Berkeley National Laboratory)

**New Physics with 21-cm Cosmology?**

*The 21-cm cosmological signal is gradually becoming a reality, offering a new insight into previously under-explored epochs. As with other cosmological observations, it is intriguing to consider what 21-cm cosmology can teach us about new physics. To address this, I will provide a concise overview of the physics behind the 21-cm cosmological signal and the effects of various new physics models on it. The discussion will then focus on hidden sector models that contain particles that scatter off baryons elastically. Specifically, I will argue that the Hydrogen Epoch of Reionization Array (HERA), aimed at measuring the 21-cm power spectrum, is likely to either confirm or exclude the possibility that DM-baryon interactions are the source of the anomalous measurement reported by the EDGES collaboration in 2018.*

### Radu Roiban (Pennsylvania State University)

**An Effective Field Theory Perspective on Higher-spin Fields and the Dynamics of Spinning Bodies**

*Gravitational interactions of higher-spin fields are of great theoretical and practical interest. On the one hand, they are a long unsolved problem strongly constrained by no-go theorems and on the other they are relevant to problems in gravitational-wave physics, where they describe spinning compact objects. In this talk we review an effective field theory approach to the classical gravitational interactions of high-spin fields and an amplitudes-based framework to integrating out gravitons and the construction of effective two-spinning-particle Hamiltonians. We present evidence for a conjectured definition of Kerr black holes from a quantum field theory perspective, identifying features that make it “the simplest” spinning body. We also discuss a possible all-order direct relation between the open-orbit observables of classical systems of two spinning particles and the eikonal phase of the four-particle scattering amplitude.*

### Kathryn Zurek (California Institute of Technology)

**Spacetime Fluctuations from Quantum Gravity in the Infrared**

*Quantum effects from gravity, based on naive EFT reasoning, are generally thought to decouple in the infrared. We present calculations, based on a simple prescription consistent with standard theoretical frameworks like AdS/CFT and JT gravity, where quantum gravity effects do not decouple but instead accumulate in the infrared. As a consequence, they might be observable in suitably sensitive measurements of spacetime.*

### Gordan Krnjaic (Fermi National Accelerator Laboratory)

**Towards a Realistic Model of Dark Atoms to Resolve the Hubble Tension**

*It has recently been shown that a subdominant hidden sector of atomic dark matter in the early universe can resolve the Hubble tension while maintaining good agreement with most precision cosmological observables. However, such a solution requires a hidden sector whose energy density ratios are the same as in our sector and whose recombination also takes place at redshift z≈1100, which presents an apparent fine tuning. We introduce a realistic model of this scenario that dynamically enforces these coincidences without fine tuning. In our setup, the hidden sector contains an identical copy of Standard Model (SM) fields, but has a smaller Higgs vacuum expectation value (VEV) and a lower temperature. The baryon asymmetries and reheat temperatures in both sectors arise from the decays of an Affleck-Dine scalar field, whose branching ratios automatically ensure that the reheat temperature in each sector is proportional to the corresponding Higgs VEV. The same setup also naturally ensures that the Hydrogen binding energy in each sector is proportional to the corresponding VEV, so the ratios of binding energy to temperature are approximately equal in the two sectors. Furthermore, our scenario predicts a correlation between the SM/hidden temperature ratio and the atomic dark matter abundance and automatically yields values for these quantities that resolve the Hubble tension.*

### Mithat Ünsal (North Carolina State University)

*I describe an anomaly-preserving compactification of four-dimensional gauge theories, including Yang-Mills theory, its supersymmetric version, and QCD, down to 2d by turning on ’t Hooft flux through a 2-torus. This provides a new framework to analytically calculate nonperturbative properties such as confinement, chiral symmetry breaking, and multi-branch structure of vacua. I give the semiclassical description of these phenomena based on the center vortices and show that it enjoys the same anomaly matching condition with the original 4d gauge theory. For YM, the long-distance theory maps to topological gauge theory (TQFT) deformed by local topological operators. We conjecture that the weak-coupling vacuum structure on small T^2 x R^2 is adiabatically connected to the strong-coupling regime in infinite volume.*

### Mithat Ünsal (North Carolina State University)

**Taming Strong Dynamics and Phase Transitions**

*Strongly coupled dynamics of QCD and other strongly coupled gauge theories remained elusive for many decades. It was believed that phenomena such as quark confinement, chiral symmetry breaking, and the emergence of the mass gap were necessarily strong coupling effects. These perspectives changed drastically over the last fifteen years. The adiabatic continuity states that strongly coupled dynamics can be continuously connected to a weak coupling regime upon judiciously formulated compactifications without any intervening phase transitions. Such continuity is impossible with thermal compactifications of gauge theories. This progress opened many new directions, leading to the discovery of many new topological excitations, confinement mechanisms, rigorous versions of semi-classical analysis, and study of calculable phase transitions. I will review these exciting developments and state some new directions.*

### Sergei Gukov (California Institute of Technology)

*What do percolation and supersymmetric QCD have in common? In theoretical physics, dualities play the role of bridges that connect two different descriptions of the same physical system. Examples include the Kramers–Wannier duality in the Ising model or the AdS/CFT correspondence in string theory. When first discovered, dualities often appear surprising and mysterious, providing a strong motivation for advancing frontiers of our understanding. In this talk we will take a look at similar bridges that connect different areas of physics or, more generally, provide deep meaningful connections between completely different disciplines.*

## 2021

### Andrey Shkerin (Fine Theoretical Physics Institute, University of Minnesota)

**Black Hole Induced False Vacuum Decay from First Principles**

*We will discuss a method to calculate the rate of false vacuum decay induced by a black hole. The method uses complex tunnelling solutions and consistently takes into account the structure of quantum vacuum associated to the black hole. We will illustrate the technique on a two-dimensional toy model of a scalar field with inverted Liouville potential in an external background of a dilaton black hole. Using this model, we will compute the exponential suppression of tunnelling from the Boulware, Hartle-Hawking and Unruh vacuum states and show that they are parametrically different. Finally, we will discuss how our results are generalized to the realistic case of black holes in four dimensions.*

### Alex Maloney (McGill University)

*I will explore the idea that certain theories of gravity are not standard quantum mechanical theories, but are instead ensemble averages of many quantum theories. This is inspired by connections between black holes, wormholes, chaos, and the dynamics of disordered systems. To study this, we will need to understand ensembles of random field theories which generalize random matrix theory. I will describe are relatively simple version of this problem which involves averages over free boson CFTs in two dimensions. In this case the ensemble average precisely reproduces the sum over geometries of an exactly solvable (but somewhat exotic)theory of quantum gravity. This is a completely solvable model of holography,and has important implications for our understanding of quantum black holes.*

### Sandipan Kundu (Johns Hopkins University)

**Causality, Higher-spin Particles, and Large N QCD**

*I will show that metastable higher-spin particles, free or interacting, cannot couple to gravity while preserving causality unless there exist higher spin states in the gravitational sector much below the Planck scale. Causality imposes an upper bound on the mass of the lightest higher spin particle in the gravity sector in terms of quantities in the non-gravitational sector. I will argue that any weakly coupled UV completion of such a theory must have a gravity sector containing infinite towers of asymptotically parallel, equispaced, and linear Regge trajectories. This implies that the gravity sector has a stringy structure with an upper bound on the string scale. I will discuss many surprising implications of the above bound for large N QCD coupled to gravity.*

### Mithat Ünsal (North Carolina State University)

**Resurgence, Lefschetz Thimbles and Hidden Topological Angles**

*I will describe aspects of resurgence in quantum mechanics and Yang-Mills theory. In three quantum mechanical systems with the same classical (double well) potential, non-supersymmetric, N=1 supersymmetric, and N=2 (extended) supersymmetric, all of which possess the same instanton solution, I will show how thinking about Lefschetz thimbles produces distinct and correct result in each case. I will provide evidence that many features of semi-classical expansion generalize to 4d YM theory. By thinking about calculable semi-classics with fractional instantons, I will show that the quantum mechanical discussion generalizes to non-supersymmetric and supersymmetric YM. If time permits, I will briefly describe coupling YM theory to a topological theory (TQFT) on a four torus, and the type of new quantum mechanical systems that emerge in the Born-Oppenheimer approximation.*