[Theory-seminars] [theory-seminars] Postdocs interviews. Friday and Monday 10am

[Alessandro Pilloni]

CEBAF Center, Room F224
Friday, January 8th

10:00am - Jeremy Green (Mainz U.)
Nucleon strange electromagnetic form factors from lattice QCD
Abstract: We report a direct lattice QCD calculation of the strange nucleon electric and magnetic form factors. By using high statistics and a variance reduction technique called hierarchical probing, we obtain a clear nonzero signal for both form factors for the first time. We fit the Q^2-dependence and determine the strange magnetic moment as well as the strange electric and magnetic radii. We compare our results to data from parity-violating electron-proton scattering and to other theoretical studies. 

10:45am - Padmanath Madanagopalan (Graz U.)
Excited heavy hadrons from lattice QCD
Abstract: As per the invitation I got, for the first five minutes I will discuss my biography, preferably focussing details beyond what is discussed in my CV. During the remaining 20 minutes I will discuss: my research experience and achievements, emphasizing heavy hadron (mesons, baryons and tetra-quarks) spectroscopy from lattice QCD, till now and the current calculations that I am involved in. Emphasis will be given on calculations involving the usage of state-of-the-art lattice technologies like derivative-based operator construction, distillation and variational method.

11:30am - Bipasha Chakraborty (Glasgow U.)
High precision tests of the Standard Model using lattice QCD
Abstract: In this talk, I will briefly discuss my research to test the Standard Model (SM) of particle physics with high precision and look for signs of new physics using first principle lattice QCD calculations, particularly, in the low energy (~ 1 GeV) regime of QCD, the SU(3) component of the SM. The anomalous magnetic moment of the muon (a_μ), measured with an impressive accuracy of 0.54 parts per million in experiment, provides one of the most stringent tests of the SM. Intriguingly, the experimentally measured anomaly disagrees by around 3 standard deviations with the calculated value from the SM. The current theoretical uncertainty is dominated by that from the calculation of the lowest order "hadronic vacuum polarisation (HVP)". Improvements in the experimental uncertainty by a factor of 4 in the upcoming experiments at Fermilab and J-PARC are expected and improvements in the theoretical determination would make the discrepancy (if it remains) really compelling. I will present my results for improving the theoretical calculation of the HVP contribution to the anomaly using our (HPQCD) new lattice QCD method (Phys.Rev. D89 (2014) 11, 114501; arXiv:1511.05870; arXiv:1512.03270).
The quark flavour sector of the SM is also known to be potentially very sensitive to new physics effects. Studying different flavour-changing processes like leptonic and semi-leptonic decays of mesons and over-constraining the elements of the Cabibbo-Kobayashi-Maskawa (CKM) unitary matrix may lead to an internal inconsistency signalling beyond Standard Model (BSM) physics. In the second part of this talk I will focus on the progress of my calculation of V_cs, the central CKM matrix element, by comparing the lattice QCD results for the scalar and vector form factors associated with D → Klν semi-leptonic decay and the experimental decay rate. 

12:15pm - Ben Hoerz (Trinity College)
Excited states from Lattice QCD
Abstract: Monte Carlo calculations in Lattice QCD can be used to study the spectrum of quantum chromodynamics in a finite box from first principles. Most experimentally observable hadrons however appear as unstable resonances in scattering amplitudes and are hence not directly accessible through Euclidean time simulations in a finite volume. Fortunately the stationary-state energies in finite volume can be related to scattering phase shifts, hence allowing us to extract infinite-volume physics from Lattice QCD computations. 
These so-called Lüscher methods open exciting prospects for the study of resonant processes from first principles. In this talk I will outline the stochastic LapH method for lattice spectroscopy, which enables us to systematically carry out this program. I will present results on pion-pion scattering from simulations at a single lattice spacing with m_pi = 240 MeV. In the isovector channel, the large L = 3.8 fm volume enables good resolution of the rho resonance shape. Preliminary results from a different ensemble are also shown, including a first-principles determination of the low-energy contribution to the hadronic vacuum polarization.

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CEBAF Center, Room F113
Monday, January 11th

10:00am - Jose Manuel Alarcon Soriano (Bonn U.)
Chiral effective field theory for hadron and nuclear physics
Abstract: In this talk I will show some recent applications of chiral effective field theory to the study of some fundamental hadronic processes, and the contribution of these results to searches of physics beyond the standard model. Finally, I will comment briefly on the combination of lattice techniques and chiral effective field theory to address many-body nuclear problems from first principles.
Nucleon strange electromagnetic form factors from lattice QCD 

10:45am - Jacobo Ruiz de Rivera (Bonn U.)
Roy-Steiner-equation analysis of pion-nucleon scattering
Abstract: A precise understanding of low-energy pion-nucleon interactions is central for many areas in nuclear and hadronic physics, ranging from the scalar couplings of the nucleon to the long-range part of two-pion-exchange potentials and three-nucleon forces in Chiral Effective Field Theory. We present a calculation that combines the general principles of analyticity, unitarity, and crossing symmetry with modern high-precision data of hadronic atoms, leading to a phenomenological description of the pion-nucleon amplitude with unprecedented rigor and accuracy. Consequences for the pion-nucleon sigma-term and the matching to Chiral Perturbation Theory will be discussed.  

11:30am - Johannes Kirscher (Hebrew U.)
Effective nuclear theories and lattice QCD
Nucleons are composite objects. Their constituents, quarks and gluons, are described by quantum chromodymanics, a theory that can be solved in discretized space time. I will outline a program to relate this solution in the multi-baryon sector to effective field theories for nuclei. The goal is a fundamental derivation of the nuclear theory, thereby parameterizing the nuclear landscape with relatively few constants of the Standard Model. After introducing this program, I will give an overview of the existing lattice-QCD data base before presenting the results for characteristic few-nucleon observables which emerge from this data. I will detail my personal contribution including the application of the pionless effective field theory and the assessment of the pion-mass dependence of nuclear peculiarities like the Phillips and Tjon correlations. The outlook on imminent projects focuses on the pion-mass-dependence of electromagnetic properties of nuclei (moments and constituent Coulomb interaction). 

12:15pm - Francesca Aceti (Valencia U.)
TBA