Bartl, Alexander (2016)
Neutrino Interactions with Supernova Matter.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung
Kurzbeschreibung (Abstract)
Massive stars end their life in an energetic explosion called a core-collapse supernova. In such a supernova, neutrinos are produced in copious number and their interactions with matter play a major role for the supernova dynamics, the observable neutrino signal, and the conditions for nucleosynthesis. In supernova simulations, neutrino reactions involving interacting nucleons (like bremsstrahlung, inelastic scattering, and the modified Urca process) are typically described by simple models, including the one-pion-exchange (OPE) approximation for nucleon-nucleon interactions, or not implemented in the case of inelastic scattering.
In this thesis, we extend the formalism to go beyond these approximations. We derive expressions for the structure factor considering neutral-current reactions in non-degenerate mixtures of neutrons and protons, an expression that combines the effect of nucleon-nucleon interactions and nuclear recoil in non-degenerate pure neutron matter, and a structure factor for charged-current processes involving interacting nucleons. In mixtures of neutrons and protons, our calculations based on chiral effective field theory (EFT) interactions show a reduction of neutrino interaction rates by a factor of two compared to the OPE approximation at typical neutrinosphere densities (10^12-10^13 g/cm^3) and beyond. This agrees with earlier work in pure neutron matter. Calculations beyond the Born approximation based on phase shifts extracted from experiment show a similar reduction at these densities, but a large enhancement at lower densities, especially for small energy transfer. We trace this effect to the large scattering lengths in the two-nucleon sector and the fact that supernova matter at subnuclear densities behaves similar to a resonant Fermi gas. In collaboration with astrophysicists, we have investigated the impact of our improved rates on the neutrino signal and the supernova dynamics using two different approaches: detailed rates to post-process profiles obtained in simulations as well as a simple approximation of our results that is directly implemented in a simulation. We find minor changes in the neutrino emission with a shift of luminosities from heavy-lepton to electron neutrinos, harder neutrino spectra, and somewhat delayed cooling of the proto-neutron star.
Three-body forces occur naturally in the framework of chiral EFT and were shown to be important in nuclear structure calculations. We present first results for neutrino rates in non-degenerate matter that include three-body interactions. In pure neutron matter, we find a significant increase of the rates and opacities compared to the chiral results only including two-body forces, both at next-to--next-to--leading order and (to a lesser extent) at next-to--next-to--next-to--leading order. Our results show smaller effects in mixtures. In addition, we look at scattering reactions, where the long-wavelength limit of the structure factor is found to work well when calculating opacities, but not the energy transfer. Compared to nuclear recoil, interactions have a significant impact on the energy transfer especially for low-energy neutrinos in high-density, high-temperature environments. Our first results for the charged-current spin relaxation rate show trends similar to the neutral-current case. Finally, we outline open questions and remaining steps towards a consistent description of neutrino-nucleon interactions based on modern nuclear forces.
Typ des Eintrags: | Dissertation | ||||
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Erschienen: | 2016 | ||||
Autor(en): | Bartl, Alexander | ||||
Art des Eintrags: | Erstveröffentlichung | ||||
Titel: | Neutrino Interactions with Supernova Matter | ||||
Sprache: | Englisch | ||||
Referenten: | Schwenk, Prof. Ph.D Achim ; Arcones Segovia, Prof. Dr. Almudena | ||||
Publikationsjahr: | Oktober 2016 | ||||
Ort: | Darmstadt | ||||
Datum der mündlichen Prüfung: | 2016 | ||||
URL / URN: | http://tuprints.ulb.tu-darmstadt.de/5713 | ||||
Kurzbeschreibung (Abstract): | Massive stars end their life in an energetic explosion called a core-collapse supernova. In such a supernova, neutrinos are produced in copious number and their interactions with matter play a major role for the supernova dynamics, the observable neutrino signal, and the conditions for nucleosynthesis. In supernova simulations, neutrino reactions involving interacting nucleons (like bremsstrahlung, inelastic scattering, and the modified Urca process) are typically described by simple models, including the one-pion-exchange (OPE) approximation for nucleon-nucleon interactions, or not implemented in the case of inelastic scattering. In this thesis, we extend the formalism to go beyond these approximations. We derive expressions for the structure factor considering neutral-current reactions in non-degenerate mixtures of neutrons and protons, an expression that combines the effect of nucleon-nucleon interactions and nuclear recoil in non-degenerate pure neutron matter, and a structure factor for charged-current processes involving interacting nucleons. In mixtures of neutrons and protons, our calculations based on chiral effective field theory (EFT) interactions show a reduction of neutrino interaction rates by a factor of two compared to the OPE approximation at typical neutrinosphere densities (10^12-10^13 g/cm^3) and beyond. This agrees with earlier work in pure neutron matter. Calculations beyond the Born approximation based on phase shifts extracted from experiment show a similar reduction at these densities, but a large enhancement at lower densities, especially for small energy transfer. We trace this effect to the large scattering lengths in the two-nucleon sector and the fact that supernova matter at subnuclear densities behaves similar to a resonant Fermi gas. In collaboration with astrophysicists, we have investigated the impact of our improved rates on the neutrino signal and the supernova dynamics using two different approaches: detailed rates to post-process profiles obtained in simulations as well as a simple approximation of our results that is directly implemented in a simulation. We find minor changes in the neutrino emission with a shift of luminosities from heavy-lepton to electron neutrinos, harder neutrino spectra, and somewhat delayed cooling of the proto-neutron star. Three-body forces occur naturally in the framework of chiral EFT and were shown to be important in nuclear structure calculations. We present first results for neutrino rates in non-degenerate matter that include three-body interactions. In pure neutron matter, we find a significant increase of the rates and opacities compared to the chiral results only including two-body forces, both at next-to--next-to--leading order and (to a lesser extent) at next-to--next-to--next-to--leading order. Our results show smaller effects in mixtures. In addition, we look at scattering reactions, where the long-wavelength limit of the structure factor is found to work well when calculating opacities, but not the energy transfer. Compared to nuclear recoil, interactions have a significant impact on the energy transfer especially for low-energy neutrinos in high-density, high-temperature environments. Our first results for the charged-current spin relaxation rate show trends similar to the neutral-current case. Finally, we outline open questions and remaining steps towards a consistent description of neutrino-nucleon interactions based on modern nuclear forces. |
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URN: | urn:nbn:de:tuda-tuprints-57138 | ||||
Sachgruppe der Dewey Dezimalklassifikatin (DDC): | 500 Naturwissenschaften und Mathematik > 530 Physik | ||||
Fachbereich(e)/-gebiet(e): | 05 Fachbereich Physik 05 Fachbereich Physik > Institut für Kernphysik 05 Fachbereich Physik > Institut für Kernphysik > Theoretische Kernphysik 05 Fachbereich Physik > Institut für Kernphysik > Theoretische Kernphysik > Kernphysik und Nukleare Astrophysik |
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Hinterlegungsdatum: | 06 Nov 2016 20:55 | ||||
Letzte Änderung: | 06 Nov 2016 20:55 | ||||
PPN: | |||||
Referenten: | Schwenk, Prof. Ph.D Achim ; Arcones Segovia, Prof. Dr. Almudena | ||||
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: | 2016 | ||||
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