Physics & Astronomy Colloquium

Cloudy - numerical simulations of non-equilibrium plasmas and their spectra

Title: Cloudy - numerical simulations of non-equilibrium plasmas and their spectraHow Stars Form

Abstract:  Most of the quantitative information we have about the universe comes from spectroscopy, most often of emission lines or the continuous broad-band spectral energy distribution. Observations cover the electromagnetic spectrum from the radio to the gamma-ray.  The material producing the spectrum is so far from thermodynamic equilibrium that concepts like temperature do not apply.  Numerical simulations of the conditions in the plasma must be done from first principles, working back to atomic cross sections and rate coefficients.  A large system of balance equations is solved to determine the level populations within atoms or molecules and the abundance of each ion or molecule.  The cloud is optically thick, so the transfer of radiation out of the cloud and reaching our telescopes must be solved simultaneously. The result is a prediction of the full spectrum with a minimum of free parameters.  Cloudy is an open-source code that solves all these problems.  It was developed almost entirely here in Lexington and is widely used across the astronomical community. I developed Cloudy for my research, and I will describe some of its applications by my group and as well as by the astronomical community.

 

Date:
-
Location:
Chem-Phys 155

Cloudy - numerical simulations of non-equilibrium plasmas and their spectra

Title: Cloudy - numerical simulations of non-equilibrium plasmas and their spectraHow Stars Form

Abstract:  Most of the quantitative information we have about the universe comes from spectroscopy, most often of emission lines or the continuous broad-band spectral energy distribution. Observations cover the electromagnetic spectrum from the radio to the gamma-ray.  The material producing the spectrum is so far from thermodynamic equilibrium that concepts like temperature do not apply.  Numerical simulations of the conditions in the plasma must be done from first principles, working back to atomic cross sections and rate coefficients.  A large system of balance equations is solved to determine the level populations within atoms or molecules and the abundance of each ion or molecule.  The cloud is optically thick, so the transfer of radiation out of the cloud and reaching our telescopes must be solved simultaneously. The result is a prediction of the full spectrum with a minimum of free parameters.  Cloudy is an open-source code that solves all these problems.  It was developed almost entirely here in Lexington and is widely used across the astronomical community. I developed Cloudy for my research, and I will describe some of its applications by my group and as well as by the astronomical community.

 

Date:
-
Location:
Chem-Phys 155

The Heavyweight W boson - an Upset to the Standard Model of Particle Physics

Host: Gardner

Title: The Heavyweight W boson - an Upset to the Standard Model of Particle Physics

Abstract: The Standard Model of particle physics has been a crowning achievement of fundamental physics, culminating in the discovery of the Higgs boson in 2012. As a quantum theory of the building blocks of matter and forces, it has been one of the most successful theories in science. The recent measurement of the mass of the W boson disagrees with the theory prediction. This upset to the Standard Model may point towards exciting new discoveries in particle physics in the coming years. We will discuss the Standard Model, the crucial role of the W boson, and how it has become the harbinger of new laws of nature. 

 
Date:
-
Location:
Chem-Phys 155

The Heavyweight W boson - an Upset to the Standard Model of Particle Physics

Host: Gardner

Title: The Heavyweight W boson - an Upset to the Standard Model of Particle Physics

Abstract: The Standard Model of particle physics has been a crowning achievement of fundamental physics, culminating in the discovery of the Higgs boson in 2012. As a quantum theory of the building blocks of matter and forces, it has been one of the most successful theories in science. The recent measurement of the mass of the W boson disagrees with the theory prediction. This upset to the Standard Model may point towards exciting new discoveries in particle physics in the coming years. We will discuss the Standard Model, the crucial role of the W boson, and how it has become the harbinger of new laws of nature. 

 
Date:
-
Location:
Chem-Phys 155

The superconducting insulator

Host:  Murthy

Title: The Superconducting Insulator

Abstract: Many two-dimensional superconductors undergo a transition to an electric insulator as a function of different parameters such as thickness, disorder, magnetic field, chemical composition etc. This superconductor-insulator-transition has been an active area of research for the last few decades, nevertheless, some fundamental questions remain unsolved. In particular, the nature of the insulating phase, which shows unconventional transport properties, is unclear. One exciting scenario suggests that this phase incorporates superconducting fluctuating islands embedded in an insulating matrix, making it exceptional and unsimilar to any conventional superconductor or insulator.

In this colloquium I will present findings, obtained by our group as well by others, demonstrating the uniqueness of this “superconducting insulator”.  These include a disorder enhanced superconducting energy gap, a novel proximity effect, unusual vortex motion and excess superconducting specific heat in the insulator.  These results provide important insight into the physics governed by the interplay between disorder and two-dimensional superconductivity. 

Date:
-
Location:
Chem-Phys 155

The superconducting insulator

Host:  Murthy

Title: The Superconducting Insulator

Abstract: Many two-dimensional superconductors undergo a transition to an electric insulator as a function of different parameters such as thickness, disorder, magnetic field, chemical composition etc. This superconductor-insulator-transition has been an active area of research for the last few decades, nevertheless, some fundamental questions remain unsolved. In particular, the nature of the insulating phase, which shows unconventional transport properties, is unclear. One exciting scenario suggests that this phase incorporates superconducting fluctuating islands embedded in an insulating matrix, making it exceptional and unsimilar to any conventional superconductor or insulator.

In this colloquium I will present findings, obtained by our group as well by others, demonstrating the uniqueness of this “superconducting insulator”.  These include a disorder enhanced superconducting energy gap, a novel proximity effect, unusual vortex motion and excess superconducting specific heat in the insulator.  These results provide important insight into the physics governed by the interplay between disorder and two-dimensional superconductivity. 

Date:
-
Location:
Chem-Phys 155

Effective field theory, factorization and renormalization: neutrino interactions, the Fermi function and more

Title:  Effective field theory, factorization and renormalization: neutrino interactions, the Fermi function and more
 
Abstract:  Precisely calculating differences between muon- and electron-neutrino interactions is difficult, but is vital for correctly interpreting neutrino oscillation experiments. I describe recent progress with powerful quantum field theory techniques to precisely determine the ratio of νe and νµ cross sections.  The beta decay Fermi function describes electron propagation in a nuclear Coulomb field, and accounts for QED radiative corrections that are enhanced at small electron velocity β or large nuclear charge Z.  Such enhanced corrections impact a variety of processes in and beyond the Standard Model, ranging from nuclear beta decay to dark matter annihilation signals.  I present the field theory factorization formula for the Fermi function and discuss implications for precision measurements. 
Date:
-
Location:
Chem-Phys 155

Effective field theory, factorization and renormalization: neutrino interactions, the Fermi function and more

Title:  Effective field theory, factorization and renormalization: neutrino interactions, the Fermi function and more
 
Abstract:  Precisely calculating differences between muon- and electron-neutrino interactions is difficult, but is vital for correctly interpreting neutrino oscillation experiments. I describe recent progress with powerful quantum field theory techniques to precisely determine the ratio of νe and νµ cross sections.  The beta decay Fermi function describes electron propagation in a nuclear Coulomb field, and accounts for QED radiative corrections that are enhanced at small electron velocity β or large nuclear charge Z.  Such enhanced corrections impact a variety of processes in and beyond the Standard Model, ranging from nuclear beta decay to dark matter annihilation signals.  I present the field theory factorization formula for the Fermi function and discuss implications for precision measurements. 
Date:
-
Location:
Chem-Phys 155

Colloquium: Photoluminescence Spectra of Emeralds from Different Origins

Trace impurity ions Cr3+ and V3+ in emerald both absorb visible light in the red and blue-violet range, giving rise to the emerald's green color. The Cr3+ impurity can also luminesce in the visible red when illuminated with laser light. We have shown that peak positions and relative intensities of R lines appearing in the photoluminescence spectrum of emerald depend upon the emerald's origin. In particular the R1 line of lab created emeralds is positioned at the shortest wavelengths, while for natural emeralds with a non-schist origin this line is found at the same or longer wavelengths, and for natural schist origin emeralds this line peaks at even longer wavelengths.1 Recently we have learned that the R1 line's peak position depends upon concentrations of trace impurities Mg2+ and Na+ in the emerald, and that the less common shifts of the R2 line's peak arise from increased concentrations of the trace impurity Li1+.

 

Refreshments will be served in CP 179 at 3:15 PM

Date:
-
Location:
CP155
Event Series:

Colloquium: LHCb: Results, Prospects and Pentaquarks?

The LHCb experiment at CERN was designed to be, and has become, the world's premier lab for studying processes where the net quark content changes. Such studies permit potentially observing the effects of particles at very high mass scales, even those with masses that (greatly) exceed the energy of the LHC itself. I will summarize the constraints placed on new high-mass particles by LHCb to-date, and also highlight a few interesting anomalies that have been seen. The LHCb physics program expanded rapidly during LHC Run 1 to include searches for dark bosons, studies of exotic tetraquark and pentaquark states, and novel probes of proton structure. I will give an overview of the current status and future prospects for each of these topics. 
 
Refreshments will be served in CP 179 at 3:15 PM
Date:
-
Location:
CP155
Event Series: