Northwestern Events Calendar

Apr
10
2019

Brown Bag Lunch Seminar Series TBA

SHOW DETAILS

When: Wednesday, April 10, 2019
12:00 PM - 1:00 PM Central

Where: Technological Institute, F160, 2145 Sheridan Road, Evanston, IL 60208 map it

Contact: Bud Robinson   (847) 491-3644

Group: Physics and Astronomy Brown Bag Lunch Seminars

Category: Academic

Description:

Speakers TBA

Apr
24
2019

Brown Bag Lunch Seminar Series: Shi Ye and Nancy Aggarwal

SHOW DETAILS

When: Wednesday, April 24, 2019
12:00 PM - 1:00 PM Central

Where: Technological Institute, F160, 2145 Sheridan Road, Evanston, IL 60208 map it

Contact: Bud Robinson   (847) 491-3644

Group: Physics and Astronomy Brown Bag Lunch Seminars

Category: Academic

Description:

Millisecond Pulsars and Black Holes in Globular Clusters

Shi Ye

Abstract--Over a hundred millisecond radio pulsars (MSPs) have been observed in globular clusters (GCs), motivating theoretical studies of the formation and evolution of these sources through stellar evolution coupled to stellar dynamics. Here we study MSPs in GCs using realistic N-body simulations with our Cluster Monte Carlo code. We show that neutron stars (NSs) formed in electron-capture supernovae (including both accretion-induced and merger-induced collapse of white dwarfs) can be spun up through mass transfer to form MSPs. Both NS formation and spin-up through accretion are greatly enhanced through dynamical interaction processes. We find that our models for average GCs at the present day with masses ≈ 2 × 10^5 solar mass
can produce up to 10 − 20 MSPs, while a very massive GC model with mass ≈ 10^6 solar mass
can produce close to 100. We show that the number of MSPs is anti-correlated with the total number of stellar-mass black holes (BHs) retained in the host cluster. The radial distributions are also affected: MSPs are more concentrated towards the center in a host cluster with a smaller number of retained BHs. As a result, the number of MSPs in a GC could be used to place constraints on its BH population. Interestingly, our models also demonstrate the possibility of dynamically forming NS–NS and NS–BH binaries in GCs, although the predicted numbers are very small.

 

Room temperature optomechanical squeezing

Nancy Aggarwal, PhD

Quantum fluctuations of light impose a fundamental limit precision optical measurements, laser interferometric detection of gravitational waves (GWs), for example. Current generation GW detectors are limited by quantum noise and plan to improve their sensitivity by injecting squeezed states of light generated by non-linear optical materials. We present an alternative technology for producing squeeze states of light using the radiation pressure interaction of light with a mechanical oscillator. Such optomechanical (OM) squeezed light sources would be widely applicable for future precision measurements because their non-linearity is independent of the laser wavelength. Previously, OM squeezers were limited to cryogenic temperatures. I will present our recent measurement of squeezed light from an OM system at room temperature [1]. Operation of a quantum OM system at room temperature not only makes its integration into complex interferometers more feasible, it also provides a resource for exploring quantum light-matter interactions in a human-perceivable environment.

May
8
2019

Brown Bag Lunch Seminar Series TBA

SHOW DETAILS

When: Wednesday, May 8, 2019
12:00 PM - 1:00 PM Central

Where: Technological Institute, F160, 2145 Sheridan Road, Evanston, IL 60208 map it

Contact: Bud Robinson   (847) 491-3644

Group: Physics and Astronomy Brown Bag Lunch Seminars

Category: Academic

Description:

Speakers TBA

May
22
2019

Brown Bag Lunch Seminar Series: Phalguni Shah and Nathaniel Odell

SHOW DETAILS

When: Wednesday, May 22, 2019
12:00 PM - 1:00 PM Central

Where: Technological Institute, F160, 2145 Sheridan Road, Evanston, IL 60208 map it

Contact: Bud Robinson   (847) 491-3644

Group: Physics and Astronomy Brown Bag Lunch Seminars

Category: Academic

Description:

Rigid Bubbles: Novel Instabilities in Colloidal Film Rupture

Phalguni Shah

When a soap bubble pops, a rupture opens up and grows on the timescale of milliseconds. Culick (1960) showed that this rupture grows at a constant rate. Recently, Petit et al. (2015) studied films that were rigidified due to their high surfactant concentration. They observed that these films developed crack-like instabilities during rupture, and their rupture velocity was slower than that predicted by Culick. We investigate whether soap films rigidified by adding colloidal spheres show similar instabilities. We rupture a flat film containing surfactant and colloidal spheres using a needle and record it with a high-speed camera at 75,000 frames per second. We control film rigidity by varying particle concentration and find that this dramatically alters rupture dynamics. The rupture opens at a rate that is non-constant and an order of magnitude slower than the Culick velocity. Additionally, we observe a wide variety of instabilities in these rupturing colloidal films. We systematically study film rupture dynamics as a function of colloid concentration and film thickness.


A Precision Measurement of the W Branching Fractions and Testing Lepton Universality at the LHC

Nathaniel Odell

With the close of Run 2 of the Large Hadron Collider, the large amount of collected data allows for probes of new physics as well as the precision measurements of fundamental physics parameters of the Standard Model. I will outline an approach for precisely measuring the leptonic branching fractions of the W boson based on data collected by the CMS detector. Further, I will describe how this measurement can be used to probe lepton universality violation in the weak sector, and possibly offer a hint of physics beyond the standard model.