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Center for Astrophysics Research and Technologies Seminar Series Information


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Monte Carlo Simulations of Awkward Actions

Tuesday April 4, 2017
2:00 pm

 Presenter:  David Amdahl (UNM)
 Series:  Nuclear, Particle, Astroparticle and Cosmology (NUPAC) Seminars
 Abstract:  Time derivatives of scalar elds occur quadratically in textbook actions. A simple Legendre
transformation turns the lagrangian into a hamiltonian that is quadratic in the momenta. The
path integral over the momenta is gaussian. Mean values of operators are euclidean path integrals
of the classical counterparts with positive weight functions. Monte Carlo simulations can estimate
such mean values.
This familiar framework falls apart when the time derivatives do not occur quadratically. The
Legrende transformation becomes dicult or so intractable that one can't nd the hamiltonian.
Even if one nds the hamiltonian, it usually is so complicated that one can't path-integrate over
the momenta and get a euclidean path integral with a positive weight function. Monte Carlo
simulations don't work when the weight function assumes negative or complex values.
This talks shows how to make path integrals without knowing the hamiltonian. It also shows
how to estimate complex path integrals by combining the Monte Carlo method with numerical
integration and a look-up table. This new method lets one estimate the energy densities of theories
that, unlike those with quadratic time derivatives, may have nite energy densities.
 Host:  Kevin Cahill
 Location:  Room 190, Physics & Astronomy

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