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Supercomputer simulations of field theories

English title Supercomputer simulations of field theories
Applicant de Forcrand Philippe
Number 137920
Funding scheme Project funding (Div. I-III)
Research institution Institut für Theoretische Physik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Theoretical Physics
Start/End 01.10.2011 - 30.09.2013
Approved amount 217'095.00
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Keywords (3)

Quantum Chromodynamics; Lattice Field Theory; Monte Carlo

Lay Summary (English)

Lead
Lay summary

Quantum Chromodynamics (QCD) describes the strong interactions of quarks
and gluons, the elementary constituents of matter.
The study of QCD by numerical Monte Carlo simulations on a lattice is
a well-established, successful approach. Thermodynamic properties of QCD
can be determined with reasonable accuracy, for an equilibrium system
where the net matter density is zero. When it is non-zero however, the
fermion determinant becomes complex, making its interpretation as
a sampling probability density impossible. Standard Monte Carlo techniques
cannot be applied. This is the notorious "sign problem".
We want to study three cases where the sign problem can be circumvented
or where interesting physics can be studied in the regime where this problem
is mild.


1) The chiral critical line of (2+1)-flavor QCD in the continuum limit.

In the mass plane of the strange quark and the up and down quarks, this
line separates the regime of first-order chiral transitions from that
of crossover, at zero baryon density. Its location turns out to be very
sensitive to cutoff effects, so that a careful continuum extrapolation
of lattice results must be performed, and is still lacking. The distance
of this chiral critical line to the physical quark mass values will tell us how deep QCD is in the crossover region, and thus give some
indication about a possible QCD chiral critical point, which is presently
the object of an experimental search in heavy ion collisions at the
colliders RHIC and LHC.

 
2) The phase diagram of lattice QCD in the strong coupling regime.

This is a follow-up to a very successful study of lattice QCD at
infinite coupling, where the complete phase diagram could be obtained,
as well as the nuclear potential and the masses of nuclei according to
their atomic number. We now want to obtain first corrections away from
the strong coupling limit, towards continuum QCD.


3) Numerical simulations of effective models of QCD at finite density.

Models of Nambu-Jona-Lasinio type have been used to understand possible
behaviours of QCD at low temperature and finite density, with analytic
approximate methods. We want to study such models with numerical
simulations, focusing in particular on a possible crystalline phase
already found in (1+1) dimension.

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Onset Transition to Cold Nuclear Matter from Lattice QCD with Heavy Quarks
Fromm Michael, Langelage Jens, Lottini Stefano, Neuman Mathias, Philipsen Owe (2013), Onset Transition to Cold Nuclear Matter from Lattice QCD with Heavy Quarks, in Physical Review Letters, 110, 122001.
Phase transitions in heavy-quark QCD from an effective theory
Fromm Michael, Langelage Jens, Lottini Stefano, Neuman Mathias, Philipsen Owe (2013), Phase transitions in heavy-quark QCD from an effective theory, in J.Phys.Conf.Ser., 432, 012033.
Numerical properties of staggered quarks with a taste-dependent mass term
de Forcrand Philippe, Kurkela Aleksi, Panero Marco (2012), Numerical properties of staggered quarks with a taste-dependent mass term, in Journal of High Energy Physics, 1204, 142-155.
A surprise with many-flavor staggered fermions in the strong coupling limit
de Forcrand Philippe, Kim Seyong, Unger Wolfgang (2012), A surprise with many-flavor staggered fermions in the strong coupling limit, in Proceedings of Science, LATTICE2012, 053.
Constraints on the two-flavor QCD phase diagram from imaginary chemical potential
Bonati Claudio, de Forcrand Philippe, D'Elia Massimo, Philipsen Owe, Sanfilippo Francesco (2012), Constraints on the two-flavor QCD phase diagram from imaginary chemical potential, in Proceedings of Science, Lattice2011, 189-195.
Continuous Time Monte Carlo for Lattice QCD in the Strong Coupling Limit
Unger Wolfgang, de Forcrand Philippe (2012), Continuous Time Monte Carlo for Lattice QCD in the Strong Coupling Limit, in Proceedings of Science, Lattice2011, 218-224.
Finite density QCD from an effective lattice theory
Philipsen Owe, Langelage Jens, Lottini Stefano, Neuman Mathias (2012), Finite density QCD from an effective lattice theory, in Proceedings of Science, ConfinementX, 218.
New algorithms and new results for strong coupling LQCD
Unger Wolfgang, de Forcrand Philippe (2012), New algorithms and new results for strong coupling LQCD, in Proceedings of Science, LATTICE2012, 194.
Towards corrections to the strong coupling limit of staggered lattice QCD
Fromm Michael, Langelage Jens, Philipsen Owe, de Forcrand Philippe, Unger Wolfgang, Miura Kotaroh (2012), Towards corrections to the strong coupling limit of staggered lattice QCD, in Proceedings of Science, Lattice2011, 212-218.
Walking near a conformal fixed point
de Forcrand Philippe, Pepe Michele, Wiese Uwe-Jens (2012), Walking near a conformal fixed point, in Proceedings of Science, LATTICE2012, 041.
Walking near a Conformal Fixed Point: the 2-d O(3) Model at theta near pi as a Test Case.
de Forcrand Philippe, Pepe Michele, Wiese Uwe-Jens (2012), Walking near a Conformal Fixed Point: the 2-d O(3) Model at theta near pi as a Test Case., in Physical Review D, 86, 075006-075010.
Continuous Time Monte Carlo for Lattice QCD in the Strong Coupling Limit
Unger Wolfgang, de Forcrand Philippe (2011), Continuous Time Monte Carlo for Lattice QCD in the Strong Coupling Limit, in Journal of Physics, 38(2011), 124190-124194.
Conformality in many-flavour lattice QCD at strong coupling
de Forcrand Philippe, Kim Seyong, Unger Wolfgang, Conformality in many-flavour lattice QCD at strong coupling, in Journal of High Energy Physics.

Collaboration

Group / person Country
Types of collaboration
Prof. Owe Philipsen, Frankfurt Univ. Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Summer School "Phase structure of gauge theories" Talk given at a conference 03.09.2013 National Taiwan University, Taipei, Taiwan de Forcrand Philippe;
Theory Seminar Individual talk 10.04.2013 University of Bern, Switzerland Langelage Jens;
Swansea Theory Group Seminar Individual talk 06.03.2013 Swansea University, Great Britain and Northern Ireland Langelage Jens;


Associated projects

Number Title Start Funding scheme
122117 Supercomputer simulations of field theories 01.10.2009 Project funding (Div. I-III)
149723 Supercomputer simulations of field theories 01.10.2013 Project funding (Div. I-III)

Abstract

Quantum Chromodynamics (QCD) describes the strong interactions of quarks and gluons, the elementary constituents of matter.The study of QCD by numerical Monte Carlo simulations on a lattice isa well-established, successful approach. Thermodynamic properties of QCDcan be determined with reasonable accuracy, for an equilibrium system where the net matter density is zero. When it is non-zero however, the fermion determinant becomes complex, making its interpretation as a sampling probability density impossible. This is the notorious ``sign problem''. We want to study three cases where the sign problem can be circumvented or where interesting physics can be studied in the regime where this problem is mild.* The chiral critical line of (2+1)-flavor QCD in the continuum limit.In the mass plane of the strange quark and the up and down quarks, thisline separates the regime of first-order chiral transitions from thatof crossover, at zero baryon density. Its location turns out to be very sensitive to cutoff effects, so that a careful continuum extrapolation of lattice results must be performed, and is still lacking. The distance of this chiral critical line to the physical quark mass values will tell us how deep QCD is in the crossover region, and thus give some indication about a possible QCD chiral critical point.* The phase diagram of lattice QCD in the strong coupling regime.This is a follow-up to a very successful study of lattice QCD at infinite coupling, where the complete phase diagram could be obtained, as well as the nuclear potential and the masses of nuclei according to their atomic number. We now want to obtain first corrections away from the strong coupling limit, toward continuum QCD.* Numerical simulations of effective models of QCD at finite density.Models of Nambu-Jona-Lasinio type have been used to understand possible behaviours of QCD at low temperature and finite density, with analytic approximate methods. We want to study such models with numerical simulations, focusing in particular on a possible crystalline phase already found in (1+1) dimension.Pursuing these three related subprojects requires the help of a postdoc, Dr. Wolfgang Unger, for whom I ask financial support for two years.
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