We study varyious ways in which machine learning can be applied to physics simulations. A central aspect is to preserve symmetries of the underlying theory also in the neural network.
For lattice gauge theory, we propose Lattice gauge equivariant Convolutional Neural Networks (L-CNNs) that preserve gauge equivariance. We demonstrate that L-CNNs can learn and generalize gauge invariant quantities that traditional convolutional neural networks are incapable of finding.
This work has been supported by the Austrian Science Fund FWF, project number P32446-N27.
Generalization capabilities of translationally equivariant neural networks
Srinath Bulusu, Matteo Favoni, Andreas Ipp, David Müller, Daniel Schuh
(arXiv:2103.14686)
Lattice gauge equivariant convolutional neural networks
Matteo Favoni, Andreas Ipp, David Müller, Daniel Schuh
(arXiv:2012.12901)
Jet momentum broadening from the Glasma
Jets are important probes of heavy ion collisions. They can provide information on the interaction of a highly energetic parton with the expanding quark-gluon plasma.
Transverse momentum broadening quantifies the modification of a hard probe in the medium.
We calculate the momentum broadening contribution from the Glasma phase, which is the initial stage right after a heavy-ion collision. We find strong time-dependence and an intrinsic anisotropy of momentum broadening in the directions transverse to the jet propagation direction.
Jet momentum broadening in the pre-equilibrium Glasma
Andreas Ipp, David Müller, Daniel Schuh
Phys.Lett.B 810 (2020) 135810
(PLB,
arXiv:2009.14206)
Anisotropic momentum broadening in the 2+1D Glasma: analytic weak field approximation and lattice simulations
Andreas Ipp, David Müller, Daniel Schuh
Phys.Rev.D 102 (2020) 7, 074001
(PRD,
arXiv:2001.10001)
Glasma simulation using colored particle-in-cell method
The Glasma is a precursor state to the quark-gluon plasma. It is created when
two highly Lorentz-contracted nuclei collide at ultra-relativistic energies.
We have created the OpenPixi open-source framework
for the simulation of the initial stages of heavy ion collisions.
This framework is inspired by the particle-in-cell method which is used for
simulating electromagnetic plasmas. In our case, we apply this method
to the strong nuclear force, also called color force, with concepts borrowed
from lattice gauge theory.
We could show that a finite nucleus thickness along the longitudinal collision direction
leads to a Gaussian rapidity profile of observables like the Glasma energy density.
This work has been supported by the Austrian Science Fund FWF, project number P26582-N27.
Progress on 3+1D Glasma simulations
Andreas Ipp, David Müller
Eur.Phys.J.A 56 (2020) 9, 243
(EPJA,
arXiv:2009.02044)
Implicit schemes for real-time lattice gauge theory
Andreas Ipp, David Müller
Eur.Phys.J. C78 (2018) no.11, 884
(EPJC,
arXiv:1804.01995)
Broken boost invariance in the Glasma via finite nuclei thickness
Andreas Ipp, David Müller
Phys.Lett. B771 (2017) 74-79
(PLB,
arXiv:1703.00017)
Simulating collisions of thick nuclei in the color glass condensate framework
Daniil Gelfand, Andreas Ipp, David Müller
Phys.Rev. D94 (2016) no.1, 014020
(PRD,
arXiv:1605.07184)
Yoctosecond photon emission from quark-gluon plasmas
High-energy heavy ion collisions at CERN LHC or RHIC can be a source of light flashes with very interesting properties.
The quark-gluon plasma produced in such collisions is a state of matter at extremely
high temperatures which consists of deconfined, but strongly interacting quarks and gluons.
Due to the extremely short time of collision, photons can be emitted at yoctoseconds (10^{-24} s) duration.
Non-trivial expansion dynamics right after the collision of two heavy ion nuclei lead to the possibility of creating double flashes at the yoctosecond scale under certain conditions.
Another aspect we studied is the polarization of photons. In non-central collisions, photons may be circularly polarized.
Yoctosecond photon pulses from quark-gluon plasmas
Andreas Ipp, Christoph H. Keitel, Jörg Evers
Phys. Rev. Lett. 103, 152301 (2009)
(PRL,
arXiv:0904.4503)
see also Media reports
Photon polarization as a probe for quark-gluon plasma dynamics
Andreas Ipp, Antonino Di Piazza, Jörg Evers, Christoph H. Keitel
Phys.Lett.B666:315-319,2008
(Phys.Lett.B,
arXiv:0710.5700)
Zeptosecond streak imaging through vacuum pair creation
We recently proposed a new concept for characterizing extremely short photon pulses down to zeptosecond (10^{-21} s) resolution. This is achieved by applying the widely used femto- and attosecond scheme of streak imaging to the high energy process of electron-positron pair creation in strong fields. Conventional streak imaging would not work at GeV energies, because the non-linear conversion material usually used would be simply destroyed by the high-intensity laser. The solution is not to use any material at all, but provide the non-linear conversion through electron-positron pair creation from vacuum in intense laser fields. We called this new method Streaking at High Energies with Electrons and Positrons ("SHEEP"). This method could provide unprecedented detection capabilities of extremely fast high-energy processes at future laser facilities like the upcoming Extreme Light Infrastructure (ELI).
Streaking at high energies with electrons and positrons
Andreas Ipp, Jörg Evers, Christoph H. Keitel, Karen Z. Hatsagortsyan
Phys. Lett. B 702:383–387, 2011
(Phys.Lett.B, arXiv:1008.0355)
Quark-Gluon plasma instabilitites
An important process on the yoctosecond timescale is QGP plasma instabilities that emerge in the expanding quark-gluon plasma in heavy ion collisions. These instabilities are the non-abelian analog of Weibel instabilities in ordinary electromagnetic plasmas. Such plasma instabilities could provide an explanation for the still not fully understood fast apparent thermalization of the plasma. A study of these instabilities requires extensive numerical simulations. The computations were performed on the Vienna Scientific Cluster (VSC).
Non-Abelian plasma instabilities: SU(3) vs. SU(2)
Andreas Ipp, Anton Rebhan, Michael Strickland
Phys. Rev. D 84, 056003 (2011)
(Phys.Rev.D, arXiv:1012.0298)
see also Media reports
QCD thermodynamics
The quark-gluon plasma is a state of matter of which the universe consisted right after the big bang. In this state, the temperatures are so high that protons and neutrons are split into their constituents, the quarks and gluons. Such a state of matter can be realized in heavy ion colliders like RHIC at Brookhaven, at the LHC at CERN near Geneva, and in a few years also at FAIR, GSI Darmstadt. An important scientific goal is to explore the phase diagram of quantum chromo-dynamics (QCD) for various temperatures and densities. We have calculated the pressure for weakly interacting, deconfined QCD up to and including forth order in a perturbative expansion in the strong coupling.
The pressure of deconfined QCD for all temperatures and quark chemical potentials
A. Ipp, K. Kajantie, A. Rebhan, A. Vuorinen
Phys.Rev. D74 (2006) 045016
(Phys.Rev. D74 (2006) 045016,
arXiv:hep-ph/0604060)
Functional renormalization group
The functional or non-perturbative renormalization group is a promising tool to describe non-perturbative phenomena, including the strong coupling limit of QCD. This method has been applied successfully to various fields of physics, for example in the description of critical exponents. We have adapted the tool for calculating thermodynamic properties like the pressure or the thermal mass of a scalar field theory and extended it to be applied to an improved truncation scheme. The improved scheme will allow to describe dynamical properties of the plasma, like decay rates or transport coefficients using the non-perturbative renormalization group.
Calculation of the pressure of a hot scalar theory within the Non-Perturbative Renormalization Group
Jean-Paul Blaizot, Andreas Ipp, Nicolás Wschebor
Nucl.Phys.A849:165-181,2011
(Nucl.Phys.A,
arXiv:1007.0991)
Perturbation theory and non-perturbative renormalization flow in scalar field theory at finite temperature
Jean-Paul Blaizot, Andreas Ipp, Ramon Mendez-Galain, Nicolas Wschebor
Nucl.Phys.A784:376-406,2007
(Nucl.Phys.A,
arXiv:hep-ph/0610004)
Non-Fermi-Liquid behavior of QCD
Anomalous contributions to the specific heat beyond the classical Landau-Fermi liquid theory are caused by long-range quasi-static transverse gauge bosons. While in ultrarelativistic quantum electrodynamics (QED) the effect is tiny, in QCD it is much more pronounced. Using a formalism based on the large flavor number limit, we could complete the argument of the leading logarithm of the specific heat and go beyond leading order to find a series in the temperature involving fractional powers. These results have direct application in the calculation of the cooling of proto-neutron-stars.
Non-Fermi-Liquid Specific Heat of Normal Degenerate Quark Matter
A. Gerhold, A. Ipp, A. Rebhan
Phys.Rev. D70 (2004) 105015
(Phys.Rev. D,
arXiv:hep-ph/0406087)
Anomalous specific heat in high-density QED and QCD
A. Ipp, A. Gerhold, A. Rebhan
Phys.Rev. D69 (2004) 011901
(Phys.Rev. D,
arXiv:hep-ph/0309019)
Larger flavor number limit of QCD
At large number of flavors (N_{f}), thermodynamic quantities like the pressure or entropy can be calculated exactly for weak and strong couplings at next-to-leading order in a 1/N_{f} expansion. It is therefore an ideal testbed for various resummation techniques that try to overcome the poor convergence properties of strict perturbation theory.
This limit turns out to be straightforwardly applicable to finite chemical potential.
It was also used to successfully test a nonperturbative expression for the entropy obtained from a Phi-derivable two-loop approximation which resums the physics of hard thermal loops.
Asymptotic thermal quark masses and the entropy of QCD in the large-N_{f} limit
Jean-Paul Blaizot, Andreas Ipp, Anton Rebhan, Urko Reinosa
Phys.Rev. D72 (2005) 125005
(Phys.Rev. D,
arXiv:hep-ph/0509052)
Study of the gluon propagator in the large-N_{f} limit at finite temperature and chemical potential for weak and strong couplings
Jean-Paul Blaizot, Andreas Ipp, Anton Rebhan
Annals Phys. 321 (2006) 2128-2155
(Annals Phys.,
arXiv:hep-ph/0508317)
Quantum Corrections to Thermodynamic Properties in the Large N_{f} Limit of the Quark Gluon Plasma
Andreas Ipp
Ph.D. thesis
(arXiv:hep-ph/0405123)
Perturbative QCD at non-zero chemical potential: Comparison with the large-N_{f} limit and apparent convergence
A. Ipp, A. Rebhan, A. Vuorinen
Phys.Rev. D69 (2004) 077901
(Phys.Rev. D69 (2004) 077901,
arXiv:hep-ph/0311200)
Thermodynamics of Large N_{f} QCD at Finite Chemical Potential
Andreas Ipp, Anton Rebhan
Journal of High Energy Physics 06 (2003) 032
(JHEP,
arXiv:hep-ph/0305030)
Data tables: Data
Comment on and erratum to "Pressure of Hot QCD at Large N_{f}"
Andreas Ipp, Guy D. Moore, Anton Rebhan
Journal of High Energy Physics 01 (2003) 037
(JHEP,
arXiv:hep-ph/0301057)
Data tables: Data