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High Energy and Nuclear Seminar (Spring 07)The group has a weekly Friday seminar as well as Tuesday brown bag lunch meeting. The later generally involves a talk by students or other members of the group, and offers an informal settings for discussion of current issues. |
| Past Seminars: Spring 06 |
Friday Seminar
Cosmic signals from the breaking of local Lorentz invariance
Hael Collins
Umass, Amherst
May 11th, 2007, 2.00pm
LGRT 1033
This talk examines how a breakdown of a locally Lorentz invariant, point-like description of nature at tiny space-time intervals would translate into a distinctive set of signals in the primordial power spectrum generated by inflation. We examine the leading irrelevant operators that are consistent with the spatial translations and rotations of a preferred, isotropically expanding, background. A few of the resulting corrections to the primordial power spectrum do not have the usual oscillatory factor, which is sometimes taken to be characteristic of a "trans-Planckian" signal. Perhaps more interestingly, one of these leading irrelevant operators reproduces exactly an effect in the power spectrum that occurs in effective descriptions of the state of the field responsible for inflation.
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Tuesday Baglunch
Back-of-the-envelope Calculations for some probable Gravitational Wave Detectors
Satya Ray
Umass, Amherst
May 8th, 2007, 12.00pm
LGRT 419B
I will start with a brief introduction to Gravitational waves. Some simple radiational aspects of these waves will be mentioned. At the end some possible detection techniques for these waves along with their resolutions will be discussed with some back of the envelope calculations.
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Friday Seminar
A Precision Measurement of the Neutral Pion Lifetime: New Results from Jefferson Lab
Rory Miskimen
UMASS - Amherst
May 4th, 2007, 2.00pm
LGRT 1033
The low energy QCD predictions for transitions between even and odd numbers of mesons have no free parameters. This remarkable result is unique in hadron physics, where reactions are generally parameterized by form factors or low energy constants. The PRIMEX collaboration at Jefferson Lab recently completed a precision measurement of the lifetime of the lightest hadron, the neutral pion. Results from the experiment will be presented and comparisons made with the chiral anomaly prediction and NLO calculations. A future extension of the experiment to 12 GeV for measurements of the eta and eta' radiative widths will be briefly discussed.
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Wednesday Colloquium
Particle Physics: Past, Present, Future
Scott Willenbrock
University of Illinois - CU
May 2nd, 2007, 4.00pm
HAS 124
I review the present status of particle physics and summarize the major discoveries of
the last ten years. The Fermilab Tevatron is currently the highest-energy particle accelerator and will
be overtaken by the CERN Large Hadron Collider in 2008. I discuss why we believe these machines will help
elucidate the mechanism that endows all elementary particles with mass, and why this is crucial to our quest
to find a unified description of the fundamental forces of nature.
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Tuesday Baglunch
Something About Cones
Nemanja Kaloper
University of California, Davis
May 1st, 2007, 12.00pm
LGRT 419B
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Friday Seminar
Standard 4-D gravity on a brane in six dimensional flux compactifications
Lorenzo Sorbo
UMASS - Amherst
April 27th, 2007, 2.00pm
LGRT 1033
We consider a six-dimensional space-time, in which two of the dimensions are compactified by a flux.
Matter can be localized on a codimension one brane coupled to the bulk gauge field and wrapped around an axis of
symmetry of the internal space. By studying the linear perturbations around this background, we show that the
gravitational interaction between sources on the brane is described by Einstein 4d gravity at large distances.
Our model provides a consistent setup for the study of gravity in a football compactification, without having to
deal with the complications of a delta-like, codimension two brane. Moreover, it allows us to identify the origin
of the problems that emerge when one takes the limit of a codimension-two brane.
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Tuesday Baglunch
The first law for boosted Kaluza-Klein black holes
Sourya Ray
Umass, Amherst
April 24th, 2007, 12.00pm
LGRT 419B
There exists black hole solutions in spacetimes with Kaluza Klein boundary conditions
i.e., spacetimes that asymptotically approach Minkowski space times a compact Ricci-flat
space. In D>4 dimensions, such spacetimes have a very rich structure. The simplest of
such spacetimes is one where the compact space is just an S1. In addition to the usual
parameters like mass, angular momentum, charge etc, such spacetimes are characterized by
the gravitational tension along the compact direction and the length of the S1 at infinity.
These quantities enter into the first law of black hole thermodynamics in a generalized sense.
Such thermodynamic relations are known for static Kaluza Klein black hole solutions. I will
show how these relations are further generalized for stationary black hole solutions which
carry momentum along the S1.
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Tuesday Baglunch
Long Distance Electromagnetic Effects
Andreas Ross
Umass, Amherst
April 17th, 2007, 12.00pm
LGRT 419B
The calculation of the Coulomb potential from the scattering amplitude of two
charged particles at the one photon exchange level in QED is a standard QFT
textbook example. But how do loops modify this tree level result?
Effective field theory methods provide a relatively convenient way to
calculate the leading long distance effects. We will show that one loop
corrections yield both classical and quantum corrections and discuss the
definition of a potential in quantum field theory. When different spins are
involved we find that the leading long distance corrections to the Coulomb
potential are universal in that their structure and coefficients do not depend
on the actual spin of the scattered particles.
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Friday Seminar
The Daya Bay Experiment: Mapping the Frontier of Neutrino
Oscillations
Jim Napolitano
Rensselaer Polytechnic Institute
April 13thth, 2007, 2.00pm
LGRT 1033
Neutrino oscillations have been discovered, and the results are
surprising. The landscape of masses and mixings of the leptons is far
different than the Cabibbo scenario for the quarks. There is one major
linchpin left, namely the magnitude of the "last" neutrino mixing angle,
which tells how the first generation interacts with the last. This angle
is much smaller than the other two, and is consistent with zero based on
existing measurements. I will review the phenomenology of neutrino
oscillations and the status of existing measurements. Then, I will
describe the Daya Bay Experiment. This is an international collaboration
aiming to measure the "last mixing angle" using neutrinos from a nuclear
reactor complex on the Pacific Ocean, just north of Hong Kong. The
experimental challenges, and our proposed solutions to them, will be
presented, along with timetables and ultimate goals.
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Tuesday Baglunch
VHE gamma ray astronomy - Data analysis by means of
neural network selection techniques
Christian Reuschle
Umass, Amherst
April 10th, 2007, 12.00pm
LGRT 419B
The task of very high energy (VHE) gamma ray astronomy is to identify
gamma ray sources between 50 GeV and 50 TeV and to study the gamma ray
production mechanism for these sources. Unfortunately, there is a very
high "pollution" of charged cosmic ray background that prevails over the
gamma ray signal in this energy range. In order to obtain a significant
signal to background ratio one must use sophisticated background
suppression techniques. In the past year, we have implemented a neural
network selection technique to gamma ray data from the Crab Pulsar in
order to better suppress cosmic ray background. In the end, we hope to
detect the pulsed gamma ray signal from the Crab, which has not been
seen in this energy range, or set new upper limits on the energies of
the pulsed signal. In my talk I will give a short introduction to the
field of VHE gamma ray astronomy and pulsar physics. Further, I will
discuss the method which we applied and present the results we obtained
during the past year.
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Friday Seminar
Effective Field Theory and Gravitational Radiation
Walter Goldberger
Yale
April 6th, 2007, 2.00pm
LGRT 1033
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Friday Seminar
Quantum Horizons of the Standard Model Landscape
Sergei Dubovsky
Harvard
March 30th, 2007, 2.00pm
LGRT 1033
The long-distance effective field theory of our Universe--the
Standard Model coupled to gravity--has a unique 4D vacuum, but we
show that it also has a landscape of lower-dimensional vacua, with
the potential for moduli arising from vacuum and Casimir energies.
For minimal Majorana neutrino masses, we find a near-continuous
infinity of AdS3xS1 vacua, with circumference ~20 microns and AdS3
length 4x1025 m. By AdS/CFT, there is a CFT2 of central charge
c~1090 which contains the Standard Model (and beyond) coupled to
quantum gravity in this vacuum. Physics in these vacua is the same as
in ours for energies between 10-1 eV and 1048 GeV, so this CFT2
also describes all the physics of our vacuum in this energy range. We
show that it is possible to realize quantum-stabilized AdS vacua as
near-horizon regions of new kinds of quantum extremal black objects
in the higher-dimensional space--near critical black strings in 4D,
near-critical black holes in 3D. The violation of the null-energy
condition by the Casimir energy is crucial for these horizons to
exist, as has already been realized for analogous non-extremal 3D
black holes by Emparan, Fabbri and Kaloper. The new extremal 3D black
holes are particularly interesting--they are (meta)stable with an
entropy independent of hbar and G_N, so a microscopic counting of the
entropy may be possible in the G_N->0 limit. Our results suggest that
it should be possible to realize the larger landscape of AdS vacua in
string theory as near-horizon geometries of new extremal black brane
solutions.
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Tuesday Baglunch
Precision Measurements of Low Energy Deuteron Photodisintegration Using Linearly Polarized Beams
Matthew Blackston
Duke University
March 27th, 2007, 12.15pm
LGRT 419B
The High Intensity Gamma-ray Source (HIGS) provides very intense, nearly mono-energetic, and nearly 100% polarized gamma-ray beams. Linearly polarized HIGS beams were used to study deuteron photodisintegration from near photodisintegration threshold up to 16 MeV. The shape of the polarized differential cross section for the d(g,n)p reaction was extracted using the 88 neutron detectors of the Blowfish array. The data are being analyzed to extract the amplitudes of the Transition Matrix Elements (TMEs) that contribute to the reaction at these energies. This is done by writing the coefficients of a Legendre polynomial expansion of the data in terms of the amplitudes and phases of the TMEs. The data were fit to determine the amplitudes of the TMEs, using the phase shifts obtained from n-p scattering data to fix the relative phases. This talk will provide a brief overview of the HIGS facility and the experimental setup, describe how the amplitudes were extracted, and compare the results to a potential model calculation from M. Schwamb and H. Arenhovel. The relationship of these results to the Gerasimov-Drell-Hearn (GDH) integrand for the deuteron will also be discussed.
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Friday Seminar
Causality in Effective Field Theories
Alejandro Jenkins
MIT
March 16th, 2007, 2.00pm
LGRT 1033
Classical causality (i.e., present responses not depending on future
stimuli) is encoded in the Kramers-Kronig relations derived from the
analytic continuation of frequency response functions. Recently, several
authors have pointed out that the field-theoretical analog, S-matrix
analyticity, constrains the sign of certain Wilson coefficients in
effective field theories. We discuss which kinds of operators should
obey such constraints and mention some possible phenomenological
consequences. We also discuss the relation between the formal S-matrix
argument and issues of superluminality and stable causality (i.e.,
avoidance of closed timelike curves) in theories with spontaneous
Lorentz violation.
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Wednesday Seminar
Minimal Flavor Violation: from Quarks to Leptons
Vincenzo Cirigliano
LANL
March 13th, 2007, 2.00pm
LGRT 1033
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Tuesday Baglunch
The role of SUSY flat directions in reheating
Marco Peloso
Univ. of Minnesota
March 13th, 2007, 12.15pm
LGRT 419B
Reheating after inflation describes all the particle physics
processes occurring from the decay of the inflaton up to the
establishment of thermal equilibrium. Due to the strong model
dependence, it is one of the most unknown stages in the history of the
universe. There is ongoing effort to determine the reheating temperature
within different scenarios (from this quantity, one can then determine
the amount of baryons and of unwanted relics, such as gravitinos,
produced by the thermal bath). It has been argued that SUSY flat
directions are naturally excited during inflation, and that they slow
down thermalization, by providing a large effective mass to the fields
they are coupled to. We discuss a nonperturbative decay channel for the
flat directions which has been generally overlooked in the literature.
It typically leads to a quick decay of the flat directions, and,
arguably, to a suppression of their delaying effect for thermalization.
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Friday Seminar
Fundamental physics and spacetime symmetries
Ralf Lehnert, MIT
MIT
March 9th, 2007, 2.00pm
LGRT 1033
Violations of spacetime symmetries have recently been identified as
promising signatures of Planck-scale physics. This talk gives an
overview over various topics in this field: The motivations for
spacetime-symmetry research, including some mechanisms for Lorentz
breakdown, are reviewed. The Standard-Model Extension (SME) for the
description of the resulting low-energy effects is introduced, and some
tests of Lorentz symmetry are discussed.
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Colloquiaum
Are we stuck to three dimensions?
The Universe on a brane and (large) extra dimensions
Lorenzo Sorbo
Umass
February 28th, 2007, 4.00pm
HAS 124
Since the 20's physicists have been wondering whether the Universe might have more than three spatial dimensions. This possibility has become more interesting with the advent of String Theory, that typically requires 9, 10 or even 25 dimensions of space. Of course, the first question one asks is: if there are many dimensions, why do we see only three of them? The traditional (Kaluza-Klein) answer is that the extra dimensions are in some sense small. Since the end of the '90s, however, a second possibility has been envisaged: maybe ordinary matter and light are confined to our three dimensional space (a "brane") while gravity can propagate in a higher dimensional space. In this case, the extra dimensions could be as large as a millimeter or even infinite. In this class of models (brane models), gravity, cosmology and accelerator physics are expected to have new spectacular signatures. In this talk I will review brane models, their history, and some of their most interesting theoretical and experimental implications.
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Tuesday Baglunch
Power Spectrum and Signatures for Cascade Inflation
Amjad Ashoorioon
Univ. of Waterloo
February 27th, 2007, 12.15pm
LGRT 419B
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Friday Seminar
Dirty Cosmology
Grant Wilson
Umass (Astronomy)
February 23rd, 2007, 2.00pm
LGRT 1033
Physicists simplify. Be it isolated cryostats for studying condensed matter, high-energy beams of protons and anti-protons, or studying the Universe as it existed at recombination; well controlled experiments are the hallmark of great discoveries. Astronomers don't have it so easy. In general we are stuck with a limited view of an unkempt, highly-nonlinear universe that is constantly evolving. Add dark matter and dark energy to the mix and the primordial soup of cosmology looks more like bouillabaisse. In this talk I will describe work we are doing at the frontier where the Universe transitions from the linear to the non-linear regime. AzTEC is a 144 element bolometric array currently tuned to image the sky at mm wavelengths. AzTEC was built at UMass and spent 2 months at the 15m James Clerk Maxwell Telescope in Hawaii where we detected over 200 new ultra-massive starburst galaxies - some of them stemming from the initial epoch of structure formation. I will give a general survey of the work we have done to date with the instrument, as well as new studies in support of dark energy experiments which we will start later this year with AzTEC on the ASTE telescope in Chile. While this work is still in its infancy, it does give us a taste of the great scientific challenges and discovery potential that awaits us in the upcoming era of the Large Millimeter Telescope.
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Tuesday Baglunch
Electromagnetic Interactions of Neutral Systems
Barry Holstein
UMASS
February 20th, 2007, 12.15pm
LGRT 419B
The electromagnetic interaction between neutral particles or between a neutral
and a charged particle is well known and arises from two photon exchange. An
example is the vanderWaals interaction which was first calculated by Casimir
and Polder nearly sixty years ago. After reviewing the physics of such
processes we show that effective field theory techniques allow the
straightforward calculation of such interactions with much less effort than in
previous methods.
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Friday Seminar
Searching for New Physics in B decays at BaBar
Gabriella Sciolla
MIT
February 16th, 2007, 2.00pm
LGRT 1033
The study of CP violation at the B factories allows us to perform quantitative tests of the CP sector of the Standard Model. Accurate measurements of the sides and angles of the Unitarity Triangle determine the parameters rho and eta of the theory, while redundant measurements of the same quantities allow us to probe physics Beyond the Standard Model. The recent measurements of the B_s mixing frequency at the Tevatron have dramatically improved our knowledge of |V_td/V_ts|, the right side of the Unitarity Triangle. This opens up a new opportunity for probing New Physics through an independent determination of the same quantity. In this talk, I will discuss how such a measurement can be made using decays of B->rho gamma and B->K* gamma, and show our recent results.
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Colloquia
Gravitational Mass and Black Hole Thermodynamics
Jennie Traschen
UMASS, Amherst
February 7th, 2007, 4.00pm
HAS 124
Gravity is about how mass determines the dynamics of spacetime, and the resulting motion of particles. A “particle” may be the earth as part of the solar system, or the Milky Way as a part of the expanding universe. It is perhaps surprising that defining the "conserved total mass of a system" turns out to be a challenging problem in general relativity. The first part of the talk will address why general relativity is different in this respect than other familiar field theories, what the resolution is for isolated systems, and how conserved gravitational charges enter into black hole thermodynamics. Then we will turn to more recent developments. The boost mass is the (unfamiliar charge) related to the (familiar) boost symmetry; gravitational tension is a new charge which arises naturally in string or brane spacetimes. The boost mass and the tension each introduce new features to the laws of black hole (thermo)dynamics. Understanding mass in our own expanding universe, turns out to be a challenging case, and we will finish with some discussion of this situation.
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Friday Seminar
Evidence for single top quark production in p-pbar collisions
Ulrich Heintz
Boston University
February 2nd, 2007, 2.00pm
LGRT 1033
The discovery of the top quark over a decade ago was based on top quarks produced in top-antitop quark pairs by the strong interaction. Since the top quark decays via the electroweak interaction it should also be possible to produce top quarks through the electroweak interaction. In this case they do not have to be produced in pairs. It is of great interest to measure the production cross section for single top quarks because it would give the first direct access to measuring the CKM matrix element Vtb. The single top production cross section is also sensitive to effects of new physics. Detecting this production process is difficult because of the small signal to background for single top production. Based on about 1 fb-1 of data, the D0 Collaboration has recently announced an excess of over 3 standard deviation significance in their single top quark search. I will present the analysis and discuss the resulting measurements of the single top production cross section and |Vtb|.
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Tuesday Baglunch
Shock waves on branes
Mohamed Anber
UMASS, Amherst
December 5th, 2006, 12.15pm
LGRT 419B
Shock waves are exact solutions of Einstein's equations that describe the gravitational waves from massless particles moving along null geodesics. These solutions play important role from quantum gravity to black hole collision. In this talk, I review the construction of these waves as well as the gravity in 2+1 dimensions. After that I show how one can obtain shock wave solutions on branes embedded in AdS spaces.
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