Seminars on Strong Interactions (and related areas)

The Nuclear Theory Group hosts a series of seminars in the Department of Physics of the University of Arizona. The current format is joint with the Particle Theory Group. See current schedule. (A preliminary schedule is in Thomas's page, and previous schedules can be found in Enberg's and Goh's pages).

Past Seminars

Thursday, Sept 8, 2005, 3:00-4:00pm, PAS 218
Baha Balantekin, University of Wisconsin-Madison
"Neutrino-Nucleus Interactions"

I will present an overview of theory of neutrino-nucleus interactions and describe various ongoing experimental efforts to measure them. I will also describe extraction of counter-terms in the effective field theory approach to the neutrino-deuteron interaction from the solar neutrino data.

Wednesday, May 4, 2005, 4:00-5:00pm, PAS 218
Renato Higa, Jefferson Lab
"Two-pion exchange and peripheral NN scattering"

In the first part of this talk I will discuss the problem of the HBChPT formalism applied to the construction of an NN potential, and compare their expressions with ours, based on the relativistic formalism by Becher and Leutwyler. In the second part I will present both results for phase shifts in peripheral waves ($L\geq 3$), and how they are influenced by the input parameters of the potential (LECs).

Monday, May 2, 2005, 4:00-5:00pm, PAS 218
Ken Hicks, Ohio University
"Pentaquarks: are they real or not?"

A new class of particles made from four quarks and one antiquark, called pentaquarks, are allowed by the rules of QCD. However, until a few years ago, there was no evidence for such particles. In 2003-4, over 10 experiments announced positive evidence for a narrow resonance near 1535 MeV, which had quantum numbers characteristic of a pentaquark. Soon after, a number of high-energy experiments showed null results to detect this particle. Could this exotic particle also be so fragile that it could not be seen as a result of the production of hadrons at high-energy, known as fragmentation? Recently, an experiment at the Thomas Jefferson National Accelerator Facility was announced for the near-threshold reaction $\gamma p \to K^+ K^0 (n)$ which also shows a null result for this resonance. In this seminar, the question of whether pentaquarks exist as narrow resonances is discussed in light of the recent experiments.

Thursday, Mar 31, 2005, 2:30-3:30pm, PAS 274
Darius Germanas, Institute of Physics, Vilnius, Lithuania
"Lower bounds on the triton and alpha particle"

A method for lower bounds calculation for the binding energies of the lightest nuclei is introduced. The algorithm is based upon the factorization of the antisymmetrizer and Hamiltonian operators, allowing an efficient computation of both lower and upper bounds for binding energies. In large model spaces, both bounds converge to exact values. For Hamiltonians which include two-body interactions only, I will illustrate the applicability of the method to three- and four-body systems.

Thursday, Feb 24, 2005, 3:30-4:30pm, PAS 218
Harald Griesshammer, TU Muenchen
"An Effective Tale of A Few Nucleons"

With new high-precision experiments offering detailed insight into Nuclear Physics, nucleons and atomic nuclei prove an outstanding theoretical challenge: The theory of strong interactions, Quantum Chromo Dynamics (QCD), looks deceptively simple at very short distances, but at distance scales of more than $\approx 0.2 \times 10^{-15} \mathrm{m}$, the search for direct solutions becomes formidable. Here, Effective Field Theory allows for simple, model-independent, systematic and rigorous computations of the properties of nuclear systems, deeply rooted in QCD. I outline the central ideas of this approach and then focus on three applications I am involved in: (1) Extracting observables from lattice simulations of QCD. (2) Predicting and parameterising the electro-magnetic structure of nucleons, as described by their polarisabilities, a measure for their stiffness against deformations. (3) Developing and applying the theory at very low energies, where it becomes particularly simple and a plethora of processes exist which are interesting both for fundamental and astrophysical questions, e.g. big-bang nucleo-synthesis, three-nucleon forces, and deuteron and neutron properties.

Wednesday, Feb 16, 2005, 3:00-4:00pm
Andreas Nogga, Forschungzentrum Juelich
"The quantum mechanical four-body problem"

Accurate and reliable solutions of the quantum mechanical four-body problem can be obtained using several techniques nowadays. One method is to rewrite the Schr÷dinger equation to Yakubovsky equations and solve them in momentum space. It is argued that for a variety of problems of interest, this is a specifically powerful approach. As an example, I will discuss some results for the alpha particle and four-body hypernuclei and their implications. The extension to scattering is formulated and an outlook to upcoming applications will be given.

Monday, Feb 14, 2005, 3:00-4:00pm
Hans Hammer, Institute for Nuclear Theory
"Universality in Few-Body Systems with Large Scattering Length"

Effective Field Theory (EFT) is a powerful method to calculate universal properties associated with a separation of scales in physical systems. Few-body systems with large scattering length are particularly interesting. They display a geometric spectrum of three-body bound states (so-called Efimov states) and log-periodic dependence of observables on the low-energy parameters characterizing the system. I will discuss an effective theory for three- and four-body systems and give an overview of applications in cold atoms and light nuclei. Two-dimensional systems, which are qualitatively very different, will also be discussed.

Thursday, Feb 10, 2005, 3:00-4:00pm
Gautam Rupak, Los Alamos National Laboratory
"Nuclear Physics from lattice QCD: Finite lattice spacing and volume effects"

Numerical calculation of Quantum Chromodynamics (QCD) using lattice QCD is the only method currently available for calculating low-energy hadronic observables directly from the fundamental theory of QCD. However, these numerical simulations are still a long way from calculating hadronic matrix elements with physically relevant light up and down quark masses. Chiral perturbation theory (ChPT) could provide a controlled, systematic extrapolation of the lattice data to the physical region. In this talk I will describe extensions of chiral perturbation theory relevant for lattice QCD that include dependence on the lattice spacing 'a' to quadratic order. Besides large quark masses and lattice spacing, finite volume effects need to be small to extract physical observables from lattice QCD. I will describe how one can use ChPT (with some modification) to extract nucleon mass from lattice calculations done even on a small volume.

Wednesday, Feb 2, 2005, 3:00-4:00pm
Sean Fleming, UC San Diego
"Soft-Collinear Effective Theory"

Much progress has been made in understanding QCD through the use of effective field theory (EFT). In this talk I present a new EFT that has been generating quite a bit of excitement recently: soft collinear effective theory (SCET). SCET describes the limit of QCD where highly energetic particles move through a soft background; a configuration which is typical in high energy scattering, and in the decay of a heavy particle to light particles. I motivate SCET by considering the specific example of the decay $B\to X_s \gamma$. The important properties of SCET are highlighted, and used in the example to illustrate some of the novel aspects of the theory. I then discuss my vision for the future of SCET, and the work that I have done which leads to the goals I outline. In that context I discuss applications of SCET to radiative $\Upsilon$ decays, to $J/\psi$ production at Belle and Babar, and to $J/\psi$ production in $\gamma$ nucleon collisions.

Monday, Jan 24, 2005, 3:00-4:00pm
Achim Schwenk, Indiana University
"Nuclear interactions from the renormalization group"

I discuss applications of the renormalization group (RG) to nuclear forces and nucleonic matter. The RG unifies all microscopic interactions used in nuclear structure applications. The resulting low-momentum interaction, called V_{low k}, restricts interactions to low momenta. This leads to perturbative three-nucleon interactions and perturbative nuclear matter. The RG thus enhances the strengths of Effective Field Theory interactions for many-body applications with theoretical error estimates. In many-body systems, the RG can also be used to decimate towards the Fermi surface as proposed by Shankar. I present results of this approach for neutron matter and show how the method is successfully applied in condensed matter physics. We predict S- and P-wave superfluid gaps in neutron matter, which are consistent with data when used in cooling simulations of neutron stars.

Thursday, Jan 20, 2005, 3:00-4:00
Raju Venugopalan, Brookhaven National Laboratory
"The demise of the structure function: K_t factorization and beyond in QCD at high energies"

A novel window of semi-hard physics opens up at collider energies. The physics of this regime, which dominates high energy cross-sections, is not easily described in the standard collinear factorization approach of perturbative QCD. It is naturally described in a classical effective theory called the Color Glass Condensate (CGC). We discuss in this framework, gluon and quark production in pp, pA and AA collisions. Cross-sections at low and moderate parton densities are described by universal "dipole" structures which obey K_t factorization. At high parton densities, "multipole" operators contribute thereby breaking K_t factorization. The renormalization group running of these multipole operators will provide a sensitive test of the CGC at future colliders.

Tuesday, Nov 2, 2004, 3:30-4:30pm
Carlos Bertulani, University of Arizona
"Mission not yet accomplished: Back to QED"

In the past years several new laboratories for the study of QED and strong interactions have started to produce results. I will explore the opportunities for study of QED under conditions of very strong fields made possible by the Heavy Ion Colliders, RHIC and the LHC.

Thursday, April 8, 2004, 3:30-4:30pm --- PAS274
Jerry Miller, University of Washington
"Even Parity Pentaquark and Stable Strange Nuclear Matter"

Tuesday, Mar 9, 2004, 3:30-4:30pm
Michael Ramsey-Musolf, California Institute of Technology
"Sub-Z Supersymmetry"

Tuesday, Feb 10, 2004, 3:30-4:30pm
Bira van Kolck, University of Arizona
"The up-down quark mass difference in pion production"

Tuesday, Sept 23, 2003, 3:30-4:30pm
Boris Gelman, University of Arizona
"Exotic Hadrons"

The spectrum of quantum chromodynamics (QCD)---the fundamental theory of strong interactions---is dominated by states with quantum numbers of either quark-antiquark (qqbar) pairs---mesons or systems of three quarks---baryons. However, these are not the only states that one expects to exist. Other states that can't be described as qqbar or qqq systems are refferred to as QCD ''exotics''. A number of recent experiments have seen signals for such states. I will discuss a number of possible new exotic hadrons that can exist and can be detected in the future.

Monday, May 12, 2003
Roy Frieden, University of Arizona
"Fisher Information and Physics"

Fisher information FI is the original "information", dating from about 1925. (Shannon's form was invented some 20 years later.) Until recently FI was merely used to diagnose the quality of an estimate of a parameter, such as the position of an electron. The basis for this is the so-called Cramer-Rao error inequality: the mean-squared error in any such estimate must equal or exceed one divided by the FI. More recently, FI has been shown to provide a basis for deriving the wave equations and distribution functions of physics. See the book "Physics from Fisher Information" , B.R. Frieden (Cambridge Univ. Press, 1998). These physical effects ultimately connect with FI because they describe the behavior of unknown parameters, whose errors therefore obey the C-R inequality above. We show specifically that the following physical effects derive from the use of FI: (a) the Heisenberg uncertainty principle; (b) the Schroedinger wave equation; (c) Newton's 2nd law and the Virial theorem of classical mechanics; and (d) the wave equation for gluons in QCD (time permitting).

Wednesday, May 7, 2003
Richard Lebed, Arizona State University
"Baryons in 1/N_c: The Classic and the Nouveau"

The 1/N_c expansion (N_c the number of QCD colors) this year celebrates its 30th anniversary; its modern quantitative application to baryons, using operator methods, celebrates its 10th. The first part of this talk reviews some of the classic works, in order to inform the audience of these methods and their successes. Recently a new phase opened, that of treating baryon resonances in 1/N_c as poles in meson-nucleon scattering amplitudes (which is indeed the way they are experimentally observed). This new approach, originally based on intuition gleaned from chiral soliton models but later found to be much more general, generates simple relationships between resonance masses and widths. But moreover, this approach is shown to be fully compatible with the operator methods, and also explains in a natural way such phenomena as the small N(1535) partial width to pi-N.

Monday, April 7, 2003
Romas Kalinauskas, Institute of Physics,Vilnius, Lithuania
"Techniques for nuclear structure calculations"

I will present some results which I do hope can be effective when elaborating the no-core shell-model approach.

Wednesday, April 2, 2003
Kirill Tuchin, Institute for Nuclear Theory
"QCD at high energies at work: DIS and Heavy-ion collisions"

Experimental data on Deep Inelastic Scattering at low x shows that parton structure functions of a hadron grow fast as x decreases. Since the probability to find a parton with given x is finite, there should be a QCD mechanism taming that growth. I discuss the physical nature of that mechanism which is known as the theory of Color Glass Condensate. I argue that ultimately the parton densities saturate which results in a certain predictions for experiments with hadrons at high energies. I emphasize the role of parton saturation in Deep Inelastic Scattering and Heavy-Ion Collisions.

Tuesday, April 1, 2003
Shmuel Nussinov, Tel-Aviv University
"A simple physicist approach to complex problems"

"Complex Problems" involving a large number, n, of elements and for which any general method of solution (presumably!) requires a large number (growing faster than any finite power of n) of elementary steps, and the P=(?)NP issue are briefly described. This is done in the context of a "proverbial" n students in a dorm example - a laymen description of the largest "clique" problem. We suggest a simple physical analog model which is easy to simulate. The n students or n vertices in a graph are represented by n points in d=n-1 dimensions, initially residing at the n vertices of a symmetric n-1 simplex and which move due to (constant) attractive/repulsive forces introduced between compatible/incompatible students or between connected/disconnected vertices in the graph. The deterministic evolution of the n points is free from local minima traps, easy to simulate, and helps with the following problems: 1) The Heuristic problem of finding "clusters" in a network, i.e, in graphs or in communication, commercial, biological, etc. systems) by physically (geometrically) clustering the representative points. 2) The Graph isomorphism problem by evolving independently via identical dynamics the simplexes corresponding to the two graphs and checking the (geometric) congruence of the later. 3) The largest clique problem. These problems are of increasing intrinsic difficulty and this reflects in our "Solutions". We briefly speculate on possible extensions to other "Complex Problems" such as the Traveling Salesman or Hamiltonian circuit problem and on possible implications in sociology, biology, neural-nets and other areas. No previous background beyond the most elementary geometry and physics (the latter even at the Aristotelean level) is required.

Thursday, March 27, 2003
Ionel Stetcu, Louisiana State University
"Can we trust the random phase approximation?"

Our understanding of nuclear structure is built upon mean-field theories such as Hartree-Fock and time-dependent Hartree-Fock. The small-amplitude limit of the latter is the random phase approximation (RPA), which is widely used to model giant resonances in nuclei. Despite this popularity, RPA has been mostly validated against toy models; tests against complex models are scarce in the literature. We perform a thorough test of the RPA against full $0\hbar\omega$ shell model (SM) calculations. We allow deformed Hartree-Fock solutions and compare results for spherical and deformed nuclei. We find reasonable agreement between RPA and SM, albeit with some significant failures. We also prove that a long-standing "theorem" regarding RPA is violated in the case of deformation. Moreover, we bring evidence that the symmetries are only approximatively and unreliably restored.

Wednesday, March 26, 2003
Matthias Burkardt, New Mexico State University
"Hadron Tomography"

High-energy Compton scattering experiments allow probing so-called generalized parton distributions (GPDs). These GPDs are related to the distribution of partons in impact parameter space. High-energy Compton scattering thus allows us to develop three dimensional images of the nucleons and nuclei, which describe how partons carrying different momentum fraction x are distributed in the transverse plane.

Wednesday, March 12, 2003
Simon Catterall, Syracuse University
"Lattice Supersymmetry and Topological Field Theory"

It is known that certain theories with extended supersymmetry can be discretized in such a way as to preserve an exact fermionic symmetry. In the simplest model of this kind, we show that this residual supersymmetric invariance is actually a BRST symmetry associated with gauge fixing an underlying local shift symmetry. Furthermore, the starting lattice action is then seen to be entirely a gauge fixing term. The corresponding continuum theory is known to be a topological field theory.

We look, in detail, at one example - supersymmetric quantum mechanics which possesses two such BRST symmetries. In this case, we show that the lattice theory can be obtained by blocking out of the continuum in a carefully chosen background metric. Such a procedure will not change the Ward identities corresponding to the BRST symmetries since they correspond to topological observables. Thus, at the quantum level, the continuum BRST symmetry is preserved in the lattice theory. Similar conclusions are reached for the two-dimensional comple Wess-Zumino model and imply that all the supersymmetric Ward identities are satisfied exactly on the lattice. Numerical results supporting these conclusions are presented.

Thursday, March 6, 2003
Christian ForssÚn, Chalmers University of Technology
"On the few-body character of light exotic nuclei"

The exploration of exotic nuclei is one of the most intriguing and fastest expanding fields in modern nuclear physics. In the studies of light nuclei having extreme N/Z ratios and small binding energies, many nuclear phenomena not encountered closer to stability have revealed themselves. Our story begins in Copenhagen 1936 and ends with a discussion of the 8B contributiuon to the solar neutrino problem. Along the way, we will discuss the peculiar electric dipole response of the Borromean systems 6He, 11Li and 14Be.

Wednesday, March 5, 2003
Giorgio Torrieri, University of Arizona
"Hadron freeze-out and particle spectra"

It is now generally accepted that a statistical hadronization model explains both abundacies and transverse momentum spectra of hadrons produced in heavy ion collisions. However, in published fits to experimental data, several different variants of statistical models have been used. Some of the ways these models differ include assumptions about chemical equilibrium, proper and improper consideration of hadron resonance contributions, and different assumptions regarding the freeze-out spatial geometry. I will discuss how these model features relate to different physical assumptions about the freeze-out dynamics of a new state of matter such as quark gluon plasma. I will then show, using both Monte Carlo simulations and the actual RHIC experiemental data, that fits to hadron spectra are capable of constraining freeze-out dynamics and distinguishing between the key physical features of the freeze-out models.

Friday, Feb 28, 2003
Marco Huertas, College of William & Mary
"Applications of effective field theory/density functional theory approach to properties of nuclei far from stability"

A new approach to the description of the nuclear-many body system that combines elements of effective field theory and density functional theory and which is fit along the valley of stability is applied to study properties of nuclei far from stability. Results of predictions for total binding energy, single-particle and single-hole binding energies, spins and parities, as well as beta transition rates of selected nuclei are presented.

Tuesday, Jan 28, 2003
Tom Luu, Institute for Nuclear Theory
"Perturbative Effective Theory within an Oscillator Basis"

The nuclear many-body effective interactions problem has been known to be highly non-perturbative. However, I show that the sources of the non-perturbative behaviour can be identified and systematically removed. The remaining theory exhibits perturbative behaviour. I present results for the deuteron and He3.

Tuesday, Jan 21, 2003
Urs Heller, American Physical Society & Brookhaven National Laboratory
"Thermodynamics Simulations with Improved Staggered Quarks"

We explore the QCD phase diagram at finite temperature using an improved staggered fermion action, the Asqtad action. We motivate the choice of action by demonstrating that it significantly reduces lattice artifacts at finite lattice spacing. The thermodynamics simulations are done with (a) 3 degenerate flavors with mass down to 1/5 the strange quark mass, and (b) 2+1 flavors with 1 mass fixed at the strange quark mass and the mass of the other two flavors as low as 1/5 m_s. We also report on first computations of quark number susceptibilities with the improved Asqtad staggered quark action. These susceptibilities are of interest because they can be related to event-by-event fluctuations in heavy ion collision experiments. Use of the improved quark action leads to a substantial reduction in lattice artifacts. This can be seen already for free fermions and carries over into our results for QCD.

Wednesday, Dec 11, 2002
David Cardamone, University of Arizona
"Two-State Model for the Decay of Superdeformed Nuclei"

The process by which superdeformed nuclei decay into a normal-deformed band is still an unresolved issue among the nuclear physics community. Most prominent theoretical models used to explain this phenomenon are based on incorrect physics: they are neither self-consistent nor correct. An alternative two-state model, originally suggested in 1999 by Stafford & Barrett, has the advantage of being simple, straightforward, and exactly solvable. Furthermore, the results are not too much altered by the relaxation of the two-level approximation to three or even more levels. Finally, the two-level model makes specific, experimentally testable predictions.

Wednesday, Dec 4, 2002
Aron Soha, Stanford University/SLAC
"Branching Fraction and CP Asymmetry in B0 -> J/psi pi0"

CP violation has recently been firmly established in the B meson system, in excellent agreement with Standard Model predictions. The opportunity now exists to probe details of the underlying mechanisms. This talk presents measurements of the branching fraction and time-dependent CP-violating asymmetry in B^0 -> J/psi pi^0 decays. The decay amplitude for this channel features both tree and penguin diagram contributions, the interference of which can yield a result for the asymmetry differing from that found in the "golden mode" B^0 -> J/psi Ks. The results are presented for data collected during 1999-2002 using the BaBar detector at the PEP-II asymmetric-energy B Factory at SLAC.

Wednesday, Nov 20, 2002
Yasushi Nara, University of Arizona
"Non-perturbative computation of gluon productions from the Color Glass Condensate in high energy heavy ion collisions"

I will present some results from the computation of classical Yang-Mills equations on the lattice. We extend previous work on high energy nuclear collisions in the Color Glass Condensate model to study collisions of finite ultrarelativistic nuclei. The change implemented is imposition of color neutrality condition at the nucleon level. The centrality dependence of gluon multiplicity, transverse energy, and elliptic flow will be shown.

Wednesday, Nov 13, 2002
Xavier Calmet, California Institute of Technology
"Non-Constant Fine Structure Constant and Grand Unified Theories"

Data coming from astrophysical measurements seems to indicate that the fine structure constant might undergo a small cosmological time shift. We discuss the implications that this result, if confirmed, would have on grand unified theories (GUTs). A connection to the symmetry breaking mechanism of the GUT gauge group will be discussed. A laboratory test of this measurement is described. Finally we study the implications of a time dependence of fundamental parameters for baryogenesis.

Wednesday, Oct. 30, 2002
Bira van Kolck, University of Arizona
"EFT of Halo Nuclei"

I will present the extension of EFT ideas from few-nucleon systems to halo nuclei. The power counting for low-lying bound states and resonances will be discussed. As a specific example, observables in nucleon-alpha scattering near threshold will be described. I will end with prospects for other applications, such as Borromean systems.

Wednesday, Oct. 16, 2002
Irina Mocioiu, University of Arizona
"Neutrino Oscillations and Matter Effects"

During the last few years experiments have provided strong evidence of neutrino oscillations. This is the first evidence of physics beyond the Standard Model. I will give a brief overview of the results of neutrino experiments. and explain how all these can be understood in terms of neutrino masses and oscillations in vacuum and in matter. A brief discussion of possible scenarios which give small neutrino masses will also be given. I will describe resonant oscillations in matter and the importance of treating a full three-flavor mixing scenario. All this will be applied to several scenarios for future long baseline neutrino oscillation experiments

Wednesday, Oct 2, 2002
Boris Gelman, University of Arizona
"Heavy Baryons in the Combined Large N and Heavy Quark Expansion"

A description of hadrons---the strongly bound states of quarks and gluons---directly from QCD requires a use of non-perturbative methods. I will briefly review two such methods---the large-N QCD framework and the heavy quark expansion. The main focus of the talk is on the heavy baryons---baryons containing a single heavy quark. The combined large N and heavy quark limit allows a model-independent description of the heavy baryons and their low-lying excited states in terms of an effective theory. The effective theory is based on an approximate symmetry---a contracted O(8) symmetry---exhibited by heavy baryons and their low-lying excited states near the combined large N and heavy quark limit. In addition to the excitation energies the effective theory can be used to describe the semi-leptonic form factors and radiative decay rates of the heavy baryons.

Wednesday, April 24, 2002
Hans Hammer, Ohio State University
"Effective field theory: from nuclear physics to cold atoms".

Effective Field Theory (EFT) provides a powerful framework that exploits a separation of scales in physical systems to perform systematically improvable, model-independent calculations. Particularly interesting are three-body systems with large two-body scattering length. These systems display universal features such as a logarithmic spectrum of shallow three-body bound states (so-called Efimov states) and a discrete scale invariance. In the EFT, a three-body force with limit cycle behavior is required at leading order for consistent renormalization.

This EFT has a wide range of applications and successfully describes phenomena ranging from nuclear physics to the physics of cold atoms. I will discuss applications to the neutron-deuteron and Lambda-deuteron systems in nuclear physics, as well as recent results for cold 4He atoms and alkali atoms in a BEC. The case of alkali atoms is particularly interesting, because their scattering length a can be tuned experimentally using Feshbach resonances. This allows one to test the dramatic a-dependence predicted by the EFT.