S-matrix studies of resonances in A=3,4,5,6, and 12 nucleon systems

Resonances of certain light nuclei are explored by studying the complex pole structures of the scattering matrices. Among other results we predict the existence of three-neutron and three-proton resonances, a small spin-orbit splitting in the low-lying He-5 and Li-5 states and the nonexistence of the soft dipole resonance in He-6.Comment: Talk given at the XVth International Conference on Few-Body Problems in Physics (22-26 July, 1997, Groningen, The Netherlands). To be published in the conference proceedings in Nucl. Phys. A. 5 pages with 2 figures. The postscript file and more information are available at http://qmc.lanl.gov/~csot

Effects of B-8 size on the low-energy Be7(p,gamma)B8 cross section

We calculate several "size-like" B-8 observables within the microscopic three-cluster model and study their potential constraints on the zero-energy astrophysical S_{17}(0) factor of the Be7(p,gamma)B8 reaction. We find within our three-cluster model that a simultaneous reproduction of the experimental data for the B-8 radius and quadrupole moment and of the B8-Li8 Coulomb displacement energy implies S_{17}(0)=(23-25) eVb.Comment: 8 pages with 1 figure. The original version with further details and more information are available at http://qmc.lanl.gov/~csot

Időben változó finomszerkezeti állandó az asztrofizikában = Temporally varying fine-structure constant in astrophysics

Tanulmálnyoztuk a csillagokbeli szén- és oxigéntermelés 3-alfa-rátától való függését. A C-12 magbeli 0+_2 állapot energiáját változtatva meghatároztuk a kis-, közepes- és nagytömegű csillagokban termelődött szén és oxigén mennyiségét. Eredményeink azt mutatják, hogy a nagytömegű csillagokbeli szén- és oxigéntermelés erősen függ a kezdeti tömegtől, és alapvető fontosságú a teljes evolúciós folyamat végigkövetése. A finomszerkezeti állandónak a közelmúltban megfigyelt kozmológiai léptékű változása azt eredményezi, hogy a C-12 atommag 0+_2 energiaszintjének helye időben változik. Ez a fentiek szerint izotóparány-eltolódáshoz vezet. Ennek eredményeként például módosulhattak a korai, fémben szegény csillagok által létrehozott gázfelhők izotóparányai, illetve a kozmológiai távolságmérésben használt Ia-típusú szupernovák szén-oxigén törzse, és így fényessége. Kifejlesztettünk egy primordiális nukleoszintézist modellező programot, és vizsgáltuk a keletkező elemgyakoriságok fizikai konstansoktól való függését. Megállapítottuk, hogy a kvarktömegek változására a Li-7 gyakorisága a leginkább érzékeny, ami esetleg oka lehet a megfigyelt primordiális litium anomáliának. A primordiális magreakcióknak az erős kölcsönhatás csatolási állandójától való függését vizsgálva azt találtuk, hogy a kritikus d(t,alfa)n reakcióbeli rezonancia poziciójára a vártnál sokkal kevésbé érzékenyek a gyakoriságok. | We have studied the dependence of the stellar carbon and oxygen production on the triple-alpha rate. By varying the 0+_2 state of C-12, we determined the amounts of carbon and oxygen, produced in low-, medium-, and high-mass stars. Our results show that the carbon- and oxygen production in massive stars strongly depend on the initial mass, and the full description of the complete stellar evolution is essential. The recently observed variation of the fine structure constant on cosmological scales leads to a temporal variation of the position of the 0+_2 state of carbon. This results in changes in the stellar isotope ratios. This may lead to changes in the isotope ratios in gas clouds produced in early metal-poor stars, or in the core and thus the brightness of type Ia supernovae, used in cosmological distance measurements. We have developed a computer model of primordial nucleosynthesis, and studied the dependence of the produced elemental abundances on the physical constants. We found that the Li-7 abundance is the most sensitive to changes in the quark masses, which may help to explain the primordial lithium anomaly. By studying the dependence of the primordial nuclear reactions on the coupling constant of the strong interaction, we have found that the elemental abundances are much less sensitive to the resonance position of the critical d(t,alpha)n reaction than expected

Parity-violating alpha-decay of the 3.56-MeV J,T=0+,1 state of Li-6

We study the parity-violating alpha+d decay of the lowest 0+ state of Li-6 in a microscopic three-cluster model. The initial bound and the final scattering states are described consistently within the same model. The parity-violating decay width is calculated in perturbation theory using the parity-nonconserving nucleon-nucleon interaction of Desplanques, Donoghue, and Holstein (DDH). We find that the decay width is sensitive to dynamical degrees of freedom which are beyond the alpha+p+n model, for example, alpha excitation and breakup. In our full model, which contains breathing excitations of the alpha particle and H-3 + He-3 rearrangement, the parity-nonconserving decay width is Gamma=3.97x10^{-9} eV, using the DDH coupling constants.Comment: LaTex with RevTe

Low-lying continuum structures in B8 and Li8 in a microscopic model

We search for low-lying resonances in the B8 and Li8 nuclei using a microscopic cluster model and a variational scattering method, which is analytically continued to complex energies. After fine-tuning the nucleon-nucleon interaction to get the known 1+ state of B8 at the right energy, we reproduce the known spectra of the studied nuclei. In addition, our model predicts a 1+ state at 1.3 MeV in B8, relative to the Be7+p threshold, whose corresponding pair is situated right at the Li7+n threshold in Li8. Lacking any experimental evidence for the existence of such states, it is presently uncertain whether these structures really exist or they are spurious resonances in our model. We demonstrate that the predicted state in B8, if it exists, would have important consequences for the understanding of the astrophysically important Be7(p,gamma)B8 reaction.Comment: 6 pages with 1 figure. The postscript file and more information are available at http://nova.elte.hu/~csot

Large-space cluster model calculations for the He3(He3,2p)He4 and H3(H3,2n)He4 reactions

The He3(He3,2p)He4 and H3(H3,2n)He4 reactions are studied in a microscopic cluster model. We search for resonances in the He3+He3 and He4+p+p channels using methods that treat the two- and three-body resonance asymptotics correctly. Our results show that the existence of a low-energy resonance or virtual state, which could influence the Be-7 and B-8 solar neutrino fluxes, is rather unlikely. Our calculated He3(He3,2p)He4 and H3(H3,2n)He4 cross sections are in a good general agreement with the experimental data.Comment: 12 pages with 3 figures. The postscript file and more information are available at http://nova.elte.hu/~csot

Comment on ``Large-space shell-model calculations for light nuclei''

In a recent publication Zheng, Vary, and Barrett reproduced the negative quadrupole moment of Li-6 and the low-lying positive-parity states of He-5 by using a no-core shell model. In this Comment we question the meaning of these results by pointing out that the model used is inadequate for the reproduction of these properties.Comment: Latex with Revtex, 1 postscript figure in separate fil

Localization of shadow poles by complex scaling

Through numerical examples we show that the complex scaling method is suited to explore the pole structure in multichannel scattering problems. All poles lying on the multisheeted Riemann energy surface, including shadow poles, can be revealed and the Riemann sheets on which they reside can be identified.Comment: 6 pages, Latex with Revtex, 3 figures (not included) available on reques

A galaxisok kialakulásának asztrofizikája és kozmológiája = Astrophysics and Cosmology of galaxy Formation

Az ELTE Atomfizika Tanszékén dolgozó kutatók elméleti asztrofizikai kutatásaiból egységes kutatási programot hoztunk létre, hosszú évekre meghatározva a Fizikai Intézeten belül az asztrofizikai alapkutatás irányát. Többek között megalkottunk egy ún. "merger tree" programot, amellyel a nagyskálás szerkezet időbeli fejlődése az eddigieknél jobban modellezhető. Elvégeztük a Sunyaev-Zel'dovich effektuson alapuló, a galaxishalmazokban várt lökéshullámok kimutathatóságának vizsgálatát (a galaxishamazok megfigyelésére adtunk új módszert). Megbecsültük, hogy az összeolvadó galaxismagok (fekete lyukak) optikai megfelelője is megtalálható a gravitációs hullámok detektálása nyomán. Mindezek jelentős eredmények a galaxisok feljődésének területén. Kimutattuk, hogy a 12C atommag energiaszintjeinek helye időben változik. Ez izotóparány-eltolódáshoz vezet, és ennek eredményeként módosulhattak a korai, fémben szegény csillagok által létrehozott gázfelhők izotóparányai, illetve a kozmológiai távolságmérésben használt Ia-típusú szupernovák szén-oxigén törzse, és így fényessége. Ezzel pontosítottuk a távoli (azaz korai) galaxisok megfigyelésére szolgáló legfontosabb módszert. Elkészült egy szemirelativisztikus magnetohidrodinamikai program, amley a kialakulás körülményeit szimulálja. Fotometrikus vöröseltolódás segítségével választottuk szét az alacsony és magas vöröseltolódású galaxis mintákat az SDSS adathalmazában, és ezzel hozzájárultunk a nagy minták elemzésének technikájához. | We have created a uniform research activity out of the previous work of the researchers at the Departmant of Atomic Physics, Eötvös University. At the same time we have defined the long term research direction in Astrophysics within the Physics Institute. Among the many results: we have created a merger-tree code to symulate the evolution of large scale structure in the Universe. We have shown that based on the Sunyaev-Zel'dovich effect we can observe the shock waves within large galaxy clusters (we effectively gave a new method to observe clusters). We also estimated that the optical counterparts of merging black hole (in galaxy centers) gravity wave events can be identified and observed. All of these are important contributions to the science of galaxy evolution. We have also shown that positions of energy levels in 12C atoms change with time. This results in a shift in isotope-ratios, and isotope-ratios in gas clouds created by early metal-poor stars can also change as a result. Similarly, this can change the ratios in type Ia supernovae, resulting in a magnitude change. We have enhanced the method of measuring galaxy distances on cosmological scales. We have written a semi-relativistic magnetohydrodynamics code that can help in understanding galaxy formation. We have separated high- and low-redshift galaxies in the SDSS sample, contributing to the development of data reduction techniques

Three-body resonances in He-6, Li-6, and Be-6, and the soft dipole mode problem of neutron halo nuclei

Using the complex scaling method, the low-lying three-body resonances of $^6$He, $^6$Li, and $^6$Be are investigated in a parameter-free microscopic three-cluster model. In $^6$He a 2$^+$, in $^6$Li a 2$^+$ and a 1$^+$, and in $^6$Be the 0$^+$ ground state and a 2$^+$ excited state is found. The other experimentally known 2$^+$ state of $^6$Li cannot be localized by our present method. We have found no indication for the existence of the predicted 1$^-$ soft dipole state in $^6$He. We argue that the sequential decay mode of $^6$He through the resonant states of its two-body subsystem can lead to peaks in the excitation function. This process can explain the experimental results in the case of $^{11}$Li, too. We propose an experimental analysis, which can decide between the soft dipole mode and the sequential decay mode.Comment: REVTEX, Submitted to Phys. Rev. C, 12 pages, 2 postscript figures are available upon request. CALTECH, MAP-16