College of Arts and Sciences

The closed universe and the CMB
Cosmic microwave background (CMB) observations put strong constraints on the spatial curvature via estimation of the parameter $\Omega_k$. This is done assuming a nearly scale-invariant primordial power spectrum. However, we found that the inflationary dynamics is modified due to the presence of spatial curvature leading to corrections to the primordial power spectrum. When evolved to the surface of last scattering, the resulting temperature anisotropy spectrum shows deficit of power at low multipoles ($\ell<20$). This may partially explain the observed $3 \sigma$ anomaly of power suppression for $\ell <30$. Since the curvature effects are limited to low multipoles,

Continue reading… Beatrice Bonga (Penn State)

Causal Structure Of Gravitational Waves In Cosmology

Despite being associated with particles of zero rest mass, electromagnetic and gravitational waves do not travel solely on the null cone in generic curved spacetimes. (That is, light does not always propagate on the light cone.) This inside-the-null-cone propagation of waves is known as the tail effect, and may have consequences for the quantitative prediction of gravitational waves from both in-spiraling binary compact stars/black holes and “Extreme-Mass-Ratio” systems. The latter consists of compact objects orbiting, and subsequently plunging into, the horizons of super-massive black holes astronomers now believe reside at the center of many (if not all) galaxies —

Continue reading… Yi-Zen Chu (University of Minnesota, Duluth)

On the development and applications of high-intensity cyclotrons in neutrino physics and energy research

The cyclotron is one of, if not the, most versatile particle accelerator ever conceived. Based on the (then revolutionary) principle of cyclic acceleration using RF frequency alternating voltage on a so-called dee, while particles are forced into circular orbits by a strong vertical magnetic field, many varieties have been developed in the 84 years since their invention by Lawrence in 1932. The fact that they are still around and oftentimes in a form that has been proposed many years ago is a testimony to their robustness and versatility.

Continue reading… Daniel Winklehner (MIT)

Soft limits, asymptotic symmetries, and inflation in Flatland

There has been much recent interest in soft limits, both of flat space S-Matrix elements and of cosmological correlation functions. I will discuss the physics probed by soft limits in cosmology and explore the connection between cosmological soft theorems and asymptotic symmetries. These ideas will be illustrated by a simple example: inflation in 2+1 dimensions.

Continue reading… Austin Joyce (Kavli Institute for Cosmological Physics, Chicago)

Non-Singular Black Holes in Massive Gravity

When starting with a static, spherically-symmetric ansatz, there are currently two types of black hole solutions in massive gravity: (i) exact Schwarzschild solutions which exhibit no Yukawa suppression at large distances and (ii) solutions which contain coordinate-invariant singularities at the horizon.  In this talk, I will present new black hole solutions which have a nonsingular horizon and can potentially be matched to Yukawa asymptotics at large distances.  These solutions recover Schwarzschild black holes in the massless limit and are thus observationally viable.”

Continue reading… Rachel Rosen (Columbia University)

Splitting and showering in the electroweak sector

We derive the splitting functions for the Standard Model electroweak sector at high energies, including the fermions, massive gauge bosons and the Higgs boson. We study the class of functions with the “ultra-collinear” behavior that is a consequence of the electroweak symmetry breaking. We stress the leading-order corrections to the “Goldstone-boson Equivalence Theorem”. We propose a novel gauge, dubbed the “Goldstone Equivalence Gauge” that practically as well as conceptually disentangles the effects from the Goldstone bosons and the gauge fields. We also demonstrate a practical scheme for multiple electroweak boson production via showering at high energies.

Continue reading… Tao Han (University of Pittsburgh)

Cosmology with Millimeter Wave LEKIDs: CMB, Spectroscopy, and Imaging with TolTEC

Millimeter-wave cameras offer a unique window on the history and dynamics of the universe. Observations of CMB polarization are setting new constraints on cosmic inflation and gravitational lensing. Imaging and spectroscopy in millimeter waves measures individual galaxies through their bolometric flux as well as C+/CO line strengths. In this talk, I will discuss aluminum LEKID detectors that can be used for all of these applications. The feed structures are directly machined in metal, and the detectors are made with a single-layer process. Lab measurements show that the 150 GHz dual-polarization detectors have photon-noise limited sensitivity,

Continue reading… Sean Bryan (Arizona State University)

*Note that the seminar may be pushed back to 11:30-12:30.

The Radial Acceleration Relation in Rotationally Supported Galaxies

We report a correlation between the radial acceleration traced by rotation curves and that predicted by the observed distribution of baryons. The same relation is followed by 2693 points in 153 galaxies with very different morphologies, masses, sizes, and gas fractions. The correlation persists even when dark matter dominates. Consequently, the dark matter contribution is fully specified by that of the baryons. The observed scatter is small and largely dominated by observational uncertainties. This radial acceleration relation is tantamount to a natural law for rotating galaxies.

Continue reading… Stacy McGaugh (CWRU Astronomy) [note time]

Scattering amplitudes and soft theorems

I will give a pedagogical introduction to the spinor helicity formalism which provides a very efficient tool for studies of on-shell scattering amplitudes in 4 dimensions. The power of this formalism will be demonstrated in a new analysis of soft photon and soft graviton theorems.

Continue reading… Henriette Elvang (University of Michigan)

Understanding Color-Kinematics Duality with a New Symmetry: From Radiation Zeros to BCJ

I discuss a new set of symmetries obeyed by tree-level gauge-theory amplitudes involving at least one gluon. The symmetry acts as a momentum-dependent shift on the color factors of the amplitude. Using our previous development of radiation vertex expansions, we prove the invariance under this color-factor shift of the n -gluon amplitude, and in fact for any amplitudes involving at least one massless gauge boson and any number of massless or massive particles in arbitrary representations of the gauge group with spin zero,

Continue reading… Bob Brown (CWRU)

Raymond Stora’s last work

Continue reading… Bryan Lynn (CWRU and University College London)