PD Dr. Oliver Bär

Profil

Zusammenfassung

Oliver Bär entwickelt theoretische Methoden zur Beschreibung von Quantenchromodynamik (QCD) auf dem Rechengitter, insbesondere durch chirale Störungstheorie. Seine Expertise liegt darin, systematische Fehler in Gitterrechnungen zu verstehen und zu korrigieren — etwa durch die Konstruktion effektiver Lagrangians für verschiedene Fermion-Formulierungen und die Berechnung von Kontaminationen durch Mehrteilchenzustände. Diese Arbeiten ermöglichen präzisere numerische Simulationen von Kernphysik und Hadronenstrukturen.

Skills

Name

PD Dr. Oliver Bär

Titel

PD Dr.

Fakultät

Mathematisch-Naturwissenschaftliche Fakultät

Institut

Institut für Physik

Arbeitsgruppe

Theoretische Physik (Phänomenologie der Elementarteilchenphysik jenseits des Standardmodells)

E-Mail

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HU-FIS-Profil

Quelle ↗

Zuletzt gescrapt

28.6.2026, 01:02:44

• Beiträge von Mehrteilchenzuständen zu hadronischen Korrelationsfunktionen mittels chiraler Störungstheorie

  Quelle ↗

  Förderer: DFG Eigene Stelle (Sachbeihilfe) Zeitraum: 02/2017 - 02/2020 Projektleitung: PD Dr. Oliver Bär

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• Chiral perturbation theory at<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="script">O</mml:mi><mml:mrow><mml:msup><mml:mrow><mml:mo>(</mml:mo><mml:mi>a</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mo>)</mml:mo></mml:math>for lattice QCD

  2004

  Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D, Particles, fields, gravitation, and cosmology · 137 Zitationen · DOI

  We construct chiral effective Lagrangian for two lattice theories: one with Wilson fermions and the other with Wilson sea fermions and Ginsparg-Wilson valence fermions. For each of these theories we construct the Symanzik action through $\mathcal{O}{(a}^{2}).$ The chiral Lagrangian is then derived, including terms of $\mathcal{O}{(a}^{2}),$ which have not been calculated before. We find that there are only few new terms at this order. Corrections to existing coefficients in the continuum chiral Lagrangian are proportional to ${a}^{2}$ and appear in the Lagrangian at $\mathcal{O}{(a}^{2}{p}^{2})$ or higher. Similarly, O(4) symmetry-breaking terms enter the Symanzik action at $\mathcal{O}{(a}^{2}),$ but contribute to the chiral Lagrangian at $\mathcal{O}{(a}^{2}{p}^{4})$ or higher. We calculate the light meson masses in chiral perturbation theory for both lattice theories. At next-to-leading order, we find that there are no $\mathcal{O}{(a}^{2})$ corrections to the valence-valence meson mass in the mixed theory due to the enhanced chiral symmetry of the valence sector.

• Chiral perturbation theory for staggered sea quarks and Ginsparg-Wilson valence quarks

  2005

  Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D, Particles, fields, gravitation, and cosmology · 102 Zitationen · DOI

  We study lattice QCD with staggered sea and Ginsparg-Wilson valence quarks. The Symanzik effective action for this mixed lattice theory, including the lattice spacing contributions of $\mathcal{O}({a}^{2})$, is derived. Using this effective theory we construct the leading-order chiral Lagrangian. The masses and decay constants of pseudoscalars containing two Ginsparg-Wilson valence quarks are computed at one-loop order.

• Simulations with different lattice Dirac operators for valence and sea quarks

  2003

  Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields · 91 Zitationen · DOI

  We discuss simulations with different lattice Dirac operators for sea and valence quarks. A goal of such a ``mixed'' action approach is to probe deeper the chiral regime of QCD by enabling simulations with light valence quarks. This is achieved by using chiral fermions as valence quarks while computationally inexpensive fermions are used in the sea sector. Specifically, we consider Wilson sea quarks and Ginsparg-Wilson valence quarks. The local Symanzik action for this mixed theory is derived to $\mathcal{O}(a),$ and the appropriate low energy chiral effective Lagrangian is constructed, including the leading $\mathcal{O}(a)$ contributions. Using this Lagrangian one can calculate expressions for physical observables and determine the Gasser-Leutwyler coefficients by fitting them to the lattice data.

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