PD Dr. Martin Hasenbusch

Die Forschung konzentriert sich auf theoretische Physik und Hochenergiephysik, insbesondere auf Gitter-QCD und statistische Modelle. Es werden Computersimulationen und numerische Methoden, vor allem Monte-Carlo-Simulationen, eingesetzt, um Phasenübergänge und kritische Phänomene zu untersuchen. Die Arbeit umfasst die Analyse von Spinmodellen, den Casimir-Effekt und Universitätsklassen innerhalb der Quantenfeldtheorie. Durch mathematische Modellierung und die Anwendung der Renormierungsgruppe werden präzise theoretische Schätzungen von kritischen Exponenten geliefert.

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• Algorithms for lattice QCD and related models

  Quelle ↗

  Förderer: DFG Eigene Stelle (Sachbeihilfe) Zeitraum: 10/2016 - 09/2018 Projektleitung: PD Dr. Martin Hasenbusch, Prof. Dr. rer. nat. Peter Uwer

• Kritische Casimirkraft zwischen Kugel und Ebenen: Monte-Carlo-Simulation von Spinmodellen

  Quelle ↗

  Förderer: DFG Eigene Stelle (Sachbeihilfe) Zeitraum: 10/2013 - 09/2015 Projektleitung: PD Dr. Martin Hasenbusch

• Kritischer Casimireffekt: Monte-Carlo-Simulationen verbesserter Modelle

  Quelle ↗

  Förderer: DFG Eigene Stelle (Sachbeihilfe) Zeitraum: 11/2008 - 10/2010 Projektleitung: PD Dr. Martin Hasenbusch

• Critical exponents and equation of state of the three-dimensional Heisenberg universality class

  2002

  Physical review. B, Condensed matter · DOI

  We improve the theoretical estimates of the critical exponents for the three-dimensional Heisenberg universality class. We find $\ensuremath{\gamma}=1.3960(9),$ $\ensuremath{\nu}=0.7112(5),$ $\ensuremath{\eta}=0.0375(5),$ $\ensuremath{\alpha}=\ensuremath{-}0.1336(15),$ $\ensuremath{\beta}=0.3689(3),$ and $\ensuremath{\delta}=4.783(3).$ We consider an improved lattice ${\ensuremath{\varphi}}^{4}$ Hamiltonian with suppressed leading scaling corrections. Our results are obtained by combining Monte Carlo simulations based on finite-size scaling methods and high-temperature expansions. The critical exponents are computed from high-temperature expansions specialized to the ${\ensuremath{\varphi}}^{4}$ improved model. By the same technique we determine the coefficients of the small-magnetization expansion of the equation of state. This expansion is extended analytically by means of approximate parametric representations, obtaining the equation of state in the whole critical region. We also determine a number of universal amplitude ratios.

• Critical behavior of the three-dimensional<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>XY</mml:mi></mml:math>universality class

  2001

  Physical review. B, Condensed matter · DOI

  We improve the theoretical estimates of the critical exponents for the three-dimensional $\mathrm{XY}$ universality class. We find $\ensuremath{\alpha}=\ensuremath{-}0.0146(8),$ $\ensuremath{\gamma}=1.3177(5),$ $\ensuremath{\nu}=0.67155(27),$ $\ensuremath{\eta}=0.0380(4),$ $\ensuremath{\beta}=0.3485(2),$ and $\ensuremath{\delta}=4.780(2).$ We observe a discrepancy with the most recent experimental estimate of $\ensuremath{\alpha};$ this discrepancy calls for further theoretical and experimental investigations. Our results are obtained by combining Monte Carlo simulations based on finite-size scaling methods, and high-temperature expansions. Two improved models (with suppressed leading scaling corrections) are selected by Monte Carlo computation. The critical exponents are computed from high-temperature expansions specialized to these improved models. By the same technique we determine the coefficients of the small-magnetization expansion of the equation of state. This expansion is extended analytically by means of approximate parametric representations, obtaining the equation of state in the whole critical region. We also determine the specific-heat amplitude ratio.