The astrophysical rapid neutron capture process or 'r process' of nucleosynthesis is believed to be responsible for the production of approximately half the heavy element abundances found in nature. This multifaceted problem remains one of the greatest open challenges in all of physics. Knowledge of nuclear physics properties such as masses, β-decay and neutron capture rates, as well as β-delayed neutron emission probabilities are critical inputs that go into calculations of r-process nucleosynthesis. While properties of nuclei near stability have been established, much still remains unknown regarding neutron-rich nuclei far from stability that may participate in the r process. Sensitivity studies gauge the astrophysical response of a change in nuclear physics input(s) which allows for the isolation of the most important nuclear properties that shape the final abundances observed in nature. This review summarizes the extent of recent sensitivity studies and highlights how these studies play a key role in facilitating new insight into the r process. The development of these tools promotes a focused effort for state-of-the-art measurements, motivates construction of new facilities and will ultimately move the community towards addressing the grand challenge of 'How were the elements from iron to uranium made?'. IntroductionOne of the major open questions in all of physics is the identification of the sites responsible for the production of the heaviest elements [1,2]. It has been understood since the 1950s that the solar system abundances of nuclei heavier than iron can be divided roughly in half based on the nucleosynthesis processes that create them. Slow neutron capture process, or s-process, nuclei lie along the middle of the valley of stability, and rapid neutron capture process, or r-process, nuclei are found on the neutron-rich side, with a third process, the p process, responsible for the significantly less abundant nuclei on the proton-rich side of stability [3,4]. Since that time much progress has been made, e.g. [5], and the basic mechanisms of and astrophysical sites for the creation of the s-process [6] and heavy p-process [7,8] nuclei are on a firm footing. The site or sites of the r process still evade definitive determination [9,10,11].The r-process pattern is extracted from the solar system abundances by subtracting the s-process and p-process contributions [12,13]. The residual pattern consists of three main abundance peaks at A ∼ 80, 130, and 195, associated with the N = 50, 82, and 126 closed shells. Building up to the heaviest r-process elements requires on the order of 100 neutrons per seed nucleus. Additional constraints come from meteoritic data, e.g. [14], and observations of r-process elements in old stars in the galactic halo, e.g. [15,16]. This data points to distinct origins for the light A < 120 ('weak') and heavy A > 120 ('main') r-process nuclei. The pattern of main r-process elements is remarkably similar among r-process enhanced halo stars and is a match to the solar residuals. Thi...

We examine the nucleosynthesis products that are produced in the outflow from rapidly accreting disks. We find that the type of element synthesis varies dramatically with the degree of neutrino trapping in the disk and therefore the accretion rate of the disk. Disks with relatively high accretion rates such asṀ ¼ 10 M s À1 can produce very neutron-rich nuclei that are found in the r-process. Disks with more moderate accretion rates can produce copious amounts of nickel, as well as the light elements such as lithium and boron. Disks with lower accretion rates such aṡ M ¼ 1 M s À1 produce large amounts of nickel, as well as some unusual nuclei such as 49 Ti, 45 Sc, 64 Zn, and 92 Mo. This wide array of potential nucleosynthesis products is due to the varying influence of electron neutrinos and antineutrinos emitted from the disk on the neutron-to-proton ratio in the outflow. We use a parameterization for the outflow and discuss our results in terms of entropy and outflow acceleration.

We consider hot accretion disk outflows from black hole-neutron star mergers in the context of the nucleosynthesis they produce. We begin with a three-dimensional numerical model of a black hole-neutron star merger and calculate the neutrino and antineutrino fluxes emitted from the resulting accretion disk. We then follow the element synthesis in material outflowing the disk along parameterized trajectories. We find that at least a weak r-process is produced, and in some cases a main r-process as well. The neutron-rich conditions required for this production of r-process nuclei stem directly from the interactions of the neutrinos emitted by the disk with the free neutrons and protons in the outflow.

We discuss how matter-enhanced active-sterile neutrino transformation in the e s and e s channels could enable the production of the rapid neutron capture (r-process͒ nuclei in neutrino-heated supernova ejecta. In this scheme the lightest sterile neutrino would be heavier than the e and split from it by a vacuum mass-squared difference of 3 eV 2 Շ␦m es 2 Շ70 eV 2 with vacuum mixing angle sin 2 2 es Ͼ10 Ϫ4 .

We present the first calculations with three flavors of collective and shock wave effects for neutrino propagation in core-collapse supernovae using hydrodynamical density profiles and the S matrix formalism. We explore the interplay between the neutrino-neutrino interaction and the effects of multiple resonances upon the time signal of positrons in supernova observatories. A specific signature is found for the inverted hierarchy and a large third neutrino mixing angle and we predict, in this case, a dearth of lower energy positrons in Cherenkov detectors midway through the neutrino signal and the simultaneous revelation of valuable information about the original fluxes. We show that this feature is also observable with current generation neutrino detectors at the level of several sigmas.