Theoretical
Nuclear Physics ++

 
Prof. Dr. Robert Roth
Institut für Kernphysik - Theoriezentrum
Schlossgartenstr. 2 - Gebäude S211
 
Welcome to the TNP++ web site. You will find information about the group, our research program, our teaching activities, and much more on these pages.
        
  • New Paper on the Hypernuclear No-Core Shell Model
    December 2017
    R. Wirth
    The No-Core Shell Model is a powerful many-body method for light nuclei. Our initial Letter, in which we presented the extension of the NCSM methodology to hypernuclei along with a first survey of light hypernuclei, omitted the details of the method and the steps needed to include hyperons into the calculation for brevity. We just submitted a longer paper to Physical Review C, which contains these missing details. There, we present the NCSM for hypernuclei in two formulations, giving the steps needed to set up a calculation. We also show precision calculations of ground- and excited-state energies of the four-body system, as well as a short survey of helium hypernuclei in the p shell.
  • Letter on Light Neutron-Rich Hypernuclei
    October 2017
    R. Wirth
    Adding a hyperon to a nucleus changes the structure of the nucleus, e.g., by lowering the ground-state energy and creating new excited states. These changes can create stable hypernuclei with unbound nucleonic cores and hypernuclei may be able to bind more neutrons than their nucleonic analogs. We submitted a study of neutron-rich helium and lithium hypernuclei to Physics Letters B, which is the first time these hypernuclei have been addressed in a calculation with a similarity-transformed chiral Hamiltonian. The transformed Hamiltonian allows us to reliably extract hypernuclear ground-state energies. With these, we investigate whether the neutron drip line of the helium and lithium hyperisotopic chains is changed compared to the nucleonic analogs.
  • Physical Review Letter on the In-Medium No-Core Shell Model
    April 2017
    R. Wirth
    Ab initio many-body methods have different strengths and weaknesses. The No-Core Shell Model (NCSM), for example, can handle odd-mass systems and excited states but is limited in particle number. Medium-mass methods like the In-Medium Similarity Renormalization Group (IM-SRG) can handle higher particle numbers but are restricted to ground-states of even nuclei. With this Physical Review Letter we present a hybrid of the two methods that has the merits of both: the In-Medium No-Core Shell Model (IM-NCSM). The IM-NCSM uses the IM-SRG to decouple a small NCSM model space from higher excitations, dramatically improving convergence of NCSM calculations. This way, the IM-NCSM enables access to excited states and electromagnetic observables of medium-mass nuclei. Check out the publication for more information.
  • hoch3 FORSCHEN - Pieces of Cosmic Puzzles
    April 2017
    R. Roth
    Based on our recent back-to-back publications in Physics Review Letters on the tetraneutron and the hyperon puzzle in neutrons stars, the TU Darmstadt has produced a little news piece for our hoch3 FORSCHEN magazine entitled 'Pieces of Cosmic Puzzles'. You can download the english version of the complete issue here and the german version here.
  • Physical Review Letter on the Tetraneutron
    October 2016
    R. Roth
    Simultaneously with our letter on hypernuclei a second letter on an equally exotic nuclear system appeared: the tetraneutron, i.e., a systems composed of 4 neutrons. In collaboration with researchers from Russia and the US we have explored the existence of a low-lying resonance in the tetraneutron and we have predicted its energy and lifetime using novel ab initio methods including continuum degrees of freedom. Our results for the resonance energy are remarkably close to a recent experimental claim by a group from RIKEN. We will certainly continue to study this elusive system, which provides a sensitive probe for the neutron-neutron interaction. Several groups within the SFB 1245, both theory and experiment, will hunt for further insights into these systems beyond the neutron dripline.
  • Physical Review Letter on Induced Hyperon-Nucleon-Nucleon Interactions
    October 2016
    R. Roth
    Unitary transformations are a key component for accelerating convergence of many-body calculations in order to reliably compute observables. These transformations induce many-body terms that have to be included in the calculation. We worked out the Similarity Renormalization Group (SRG) transformation of hyperon-nucleon interactions at the three-body level and can now precisely compute binding and excitation energies of hypernuclei. The induced three-body terms are stronger than expected and their appearance links into a long-standing puzzle in the physics of neutron stars. Check out the publications section...
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