Narrow Results

Neutrinos play the critical roles in nucleosyntheses of light-to-heavy mass elements in core-collapse supernovae (SNe). The light element synthesis is affected strongly by neutrino oscillations (MSW effect) through the ν-process in outer layers of supernova explosions. Specifically the ⁷Li and ¹¹B yields increase by factors of 1.9 and 1.3 respectively in the case of large mixing angle solution, normal mass hierarchy, and sin² 2θ₁₃ = 2 × 10⁻³ compared to those without the oscillations. In the case of inverted mass hierarchy or nonadiabatic 13-mixing resonance, the increment of their yields is much smaller. We thus propose that precise constraint on mass hierarchy and sin² 2θ₁₃ is given by future observations of Li/B ratio or Li abundance in stars and presolar grains which are made from supernova ejecta. Gamma ray burst (GRB) nucleosynthesis in contrast is not affected strongly by thermal neutrinos from the central core which culminates in black hole (BH), although the effect of neutrinos from proto-neutron star prior to black hole formation is still unknown. We calculate GRB nucleosynthesis by turning off the thermal neutrinos and find that the abundance pattern is totally different from ordinary SN nucleosynthesis which satisfies the universality to the solar abundance pattern.

We construct the error distribution of ${}^7\mathrm{\text{Li}}$ abundance measurements for 66 observations (with error bars) used by Spite et al. (2012) that give $\mathrm{\text{A(Li)}}=2.21\pm 0.065$ (median and $1\sigma$ symmetrized error). This error distribution is somewhat non-Gaussian, with larger probability in the tails than is predicted by a Gaussian distribution. The 95.4% confidence limits are $3.0\sigma$ in terms of the quoted errors. We fit the data to four commonly used distributions: Gaussian, Cauchy, Student’s t and double exponential with the center of the distribution found with both weighted mean and median statistics. It is reasonably well described by a widened $n=8$ Student’s t distribution. Assuming Gaussianity, the observed A(Li) is $6.5\sigma$ away from that expected from standard Big Bang Nucleosynthesis (BBN) given the Planck observations. Accounting for the non-Gaussianity of the observed A(Li) error distribution reduces the discrepancy to $4.9\sigma$, which is still significant.

We briefly review the physics of Big Bang Nucleosynthesis (BBN). We present, moreover, some recent results on active-sterile neutrino oscillations in the early universe and on their effects on BBN.

Dirac showed that the existence of one magnetic pole in the universe could offer an explanation of the discrete nature of the electric charge. Magnetic poles appear naturally in most grand unified theories. Their discovery would be of greatest importance for particle physics and cosmology. The intense experimental search carried thus far has not met with success. I propose a universe with magnetic poles which are not observed free because they hide in deeply bound monopole–antimonopole states named monopolium. I discuss the realization of this proposal and its consistency with known cosmological features. I furthermore analyze its implications and the experimental signatures that confirm the scenario.

The importance of nuclear reactions in low-density astrophysical plasmas with ion temperatures T ≥10¹⁰ K has been recognized for more than thirty years. However, the lack of comprehensive data banks of relevant nuclear reactions and the limited computational power have not previously allowed detailed theoretical studies. Recent developments in these areas make it timely to conduct comprehensive studies on the nuclear properties of very hot plasmas formed around compact relativistic objects such as black holes and neutron stars. Such studies are of great interest in the context of scientific programs of future low-energy cosmic γ-ray spectrometry. In this work, using the publicly available code TALYS, we have built a large nuclear network relevant for temperatures exceeding 10¹⁰ K. We have studied the evolution of the chemical composition and accompanying prompt gamma-ray emission of such high-temperature plasmas. We present the results on the abundances of light elements D, T, ³He, ⁴He, ⁶Li, ⁷Li, ⁹Be, ¹⁰B, ¹¹B, and briefly discuss their implications on the astrophysical abundances of these elements.

In the last decade, enormous progress has been achieved in the understanding of the various facets of coalescing double neutron star and neutron black hole binary systems. One hopes that the mergers of such compact binaries can be routinely detected with the advanced versions of the ground-based gravitational wave detector facilities, maybe as early as in 2016. From the theoretical side, there has also been mounting evidence that compact binary mergers could be major sources of heavy elements and these ideas have gained recent observational support from the detection of an event that has been interpreted as a "macronova", an electromagnetic transient powered by freshly produced, radioactively decaying heavy elements. In addition, compact binaries are the most plausible triggers of short gamma-ray bursts (sGRBs) and the last decade has witnessed the first detection of a sGRB afterglow and subsequent observations have delivered a wealth of information on the environments in which such bursts occur. To date, compact binary mergers can naturally explain most — though not all — of the observed sGRB properties. This paper reviews major recent developments in various areas related to compact binary mergers.

After the big bang, production of heavy elements in the early universe takes place starting from the formation of the first (Pop III) stars, their evolution, and explosion. The Pop III supernova (SN) explosions have strong dynamical, thermal, and chemical feedback on the formation of subsequent stars and evolution of galaxies. However, the nature of Pop III stars/supernovae (SNe) have not been well-understood. The signature of nucleosynthesis yields of the first SN can be seen in the elemental abundance patterns observed in extremely metal-poor (EMP) stars. We show that the abundance patterns of EMP stars, e.g. the excess of C, Co, Zn relative to Fe, are in better agreement with the yields of hyper-energetic explosions (Hypernovae, (HNe)) rather than normal supernovae. We note the large variation of the abundance patterns of EMP stars propose that such a variation is related to the diversity of the GRB-SNe and posssibly superluminous supernovae (SLSNe). For example, the carbon-enhanced metal-poor (CEMP) stars may be related to the faint SNe (or dark HNe), which could be the explosions induced by relativistic jets. Finally, we examine the various mechanisms of SLSNe.

This review focuses on nuclear reactions in astrophysics and, more specifically, on reactions with light ions (nucleons and α particles) proceeding via the strong interaction. It is intended to present the basic definitions essential for studies in nuclear astrophysics, to point out the differences between nuclear reactions taking place in stars and in a terrestrial laboratory, and to illustrate some of the challenges to be faced in theoretical and experimental studies of those reactions. The discussion revolves around the relevant quantities for astrophysics, which are the astrophysical reaction rates. The sensitivity of the reaction rates to the uncertainties in the prediction of various nuclear properties is explored and some guidelines for experimentalists are also provided.

The collapsar scenario for long-duration gamma ray bursts (GRBs) has been proposed as a possible astrophysical site for r-process nucleosynthesis. We summarize the status of r-process nucleosynthesis calculations of our group and others in the context of a magnetohydrodynamics + neutrino-heated collapsar model. In the simulations of our group, we begin with a relativistic magnetohydrodynamic model including ray-tracing neutrino transport to describe the development of the black hole accretion disk and the neutrino heating of the funnel region above the black hole. The late-time evolution of the associated jet was then followed using axisymmetric special relativistic hydrodynamics. We utilized representative test particles to follow the temperature, entropy, electron fraction and density for material flowing within the jet from ejection from the accretion disk until several thousand kilometer above the black hole as temperatures fall from 9×10⁹ to 3×10⁸ K. The evolution of nuclear abundances from nucleons to heavy nuclei for ejected test particle trajectories has been solved in a large nuclear reaction network. It was found that an r-process-like abundance distribution forms in material ejected in the collapsar jet.

Primordial nucleosynthesis remains as one of the pillars of modern cosmology. It is the testing ground upon which many cosmological models must ultimately rest. It is our only probe of the universe during the important radiation-dominated epoch in the first few minutes of cosmic expansion. This paper reviews the basic equations of space-time, cosmology, and big bang nucleosynthesis. We also summarize the current state of observational constraints on primordial abundances along with the key nuclear reactions and their uncertainties. We summarize which nuclear measurements are most crucial during the big bang. We also review various cosmological models and their constraints. In particular, we analyze the constraints that big bang nucleosynthesis places upon the possible time variation of fundamental constants, along with constraints on the nature and origin of dark matter and dark energy, long-lived supersymmetric particles, gravity waves, and the primordial magnetic field.

This paper examines nucleosynthesis in a low-mass neutron star crust that loses mass due to accretion in a close binary system and reaching a hydrodynamically unstable configuration explodes. The r-process proceeds mainly in the inner crust. Nucleosynthesis in the outer crust is an explosive process with a sharp increase in temperature caused by an outward-propagating shockwave. The number of heavy elements produced in a low-mass neutron star crust during the explosion is approximately 0.041 $M_{\odot }$, which exceeds the number of heavy elements ejected as jets in the neutron star merger scenario.

²⁶Al is a long-life radioactive isotope with a half lifetime of near 1 Myr. The origin of Galactic ²⁶Al is dominated by massive stars and their core-collapse supernovae. Detections of 1809 keV emission from ²⁶Al provide direct evidence that nucleosynthesis is ongoing in the Galaxy. The gamma-ray line shapes reflect the dynamics of the ejected isotopes in the interstellar medium and then probe properties of ISM and Galactic rotation effect. Gamma-ray emissions of ²⁶Al in the Galaxy are studied with the high spectral resolution INTEGRAL spectrometer (SPI). We carry out the first spectral survey of ²⁶Al gamma-ray line emission along the Galactic plane. The ²⁶Al line energy shifts reflect the large-scale Galactic rotation. The ²⁶Al intensity is brighter in the 4th than in the 1st quadrant (ratio ~ 1.3); the ²⁶Al line toward the direction of the Aquila region appears somewhat broadened; a latitudinal scale height of pc for ²⁶Al in the inner Galaxy is determined. Strong ²⁶Al emission signal is detected in the nearby star-formation regions Sco-Cen and Cygnus. The ²⁶Al line shapes in star-formation regions provide a clue to constrain the kinematic properties of ISM. In addition, we derive the flux ratio of ⁶⁰Fe/²⁶Al ~ 15% which can be directly compared with theoretical predictions. More theoretical work on nuclear reactions, massive star evolution models deserves improvements.

Cross sections of nuclear reactions relevant for astrophysics are crucial ingredients to understand the energy generation inside stars and the synthesis of the elements. At astrophysical energies, nuclear cross sections are often too small to be measured in laboratories on the Earth surface, where the signal would be overwhelmed by the cosmic-ray induced background.

LUNA is a unique Nuclear Astrophysics experiment located at Gran Sasso National Laboratories. The extremely low background achieved at LUNA allows to measure nuclear cross sections directly at the energies of astrophysical interest. Over the years, many crucial reactions involved in stellar hydrogen burning as well as Big Bang nucleosynthesis have been measured at LUNA.

The present contribution provides an overview on underground Nuclear Astrophysics as well as the latest results and future perspectives of the LUNA experiment.

In the last years the ${}^{19}\mathrm{\text{F}}{(\mathrm{\text{p}},\alpha )}^{16}$O and the ${}^{19}$F($\alpha$,p)${}^{22}$Ne reactions have been studied via the Trojan Horse Method in the energy range of interest for astrophysics. These are the first experimental data available for the main channels of ${}^{19}$F destruction that entirely cover the energy regions typical of the stellar H- and He- burning. In both cases the reaction rates are significantly larger than the previous estimations available in the literature. We present here a re-analysis of the fluorine nucleosynthesis in Asymptotic Giant Branch stars by employing in state-of-the-art models of stellar nucleosynthesis the THM reaction rates for ${}^{19}$F destruction.

Big Bang Nucleosynthesis (BBN) requires several nuclear physics inputs and nuclear reaction rates. An up-to-date compilation of direct cross sections of $\mathrm{\text{d(d, p)t}}$, ${\mathrm{\text{d(d, n)}}}^3$He and ${}^3\mathrm{\text{He}}{(\mathrm{\text{d, p}})}^4$He reactions is given, being these ones among the most uncertain bare-nucleus cross sections. An intense experimental effort has been carried on in the last decade to apply the Trojan Horse Method (THM) to study reactions of relevance for the BBN and measure their astrophysical S(E)-factor. The reaction rates and the relative error for the four reactions of interest are then numerically calculated in the temperature ranges of relevance for BBN $(0.01<{\mathrm{\text{T}}}_9<10)$. These value were then used as input physics for primordial nucleosynthesis calculations in order to evaluate their impact on the calculated primordial abundances and isotopical composition for H, He and Li. New results on the ${}^7\mathrm{\text{Be}}{(\mathrm{\text{n}},\alpha )}^4$He reaction rate were also taken into account.These were compared with the observational primordial abundance estimates in different astrophysical sites. Reactions to be studied in perspective will also be discussed.

The ⁶Li(p,γ)⁷Be reaction is involved in many astrophysical scenario, ranging from Big Bang Nucleosynthesis to pre-main sequence stellar evolution and solar neutrino.

At astrophysical energies, proton capture on ⁶Li proceeds through the ⁶Li(p,α)³He and the ⁶Li(p,γ)⁷Be reactions. A recent measurement of the ⁶Li(p,γ)⁷Be cross section revealed a possible resonance-like structure at center of mass energy of 195 keV. The observed S-factor could be reproduced introducing a new ⁷Be excited state with E ≈ 5800 keV and J^π = (1/2⁺, 3/2⁺). If confirmed, such excited state might also correspond to a resonance in the ³He(⁴He,γ)⁷Be reaction.

A new measurement of the ⁶Li(p,γ)⁷Be cross section at proton energies between 80 and 400 keV has been performed at the Laboratory for Underground Nuclear Astrophysics. A description of the experimental setup and preliminary results of the data analysis is provided.

In the present report the influence of fission mass distribution model on the final abundance of heavy elements in the matter, ejected during neutron star mergers is discussed. Different models of fission fragment mass distribution for exotic nuclei were applied to the r-process, calculated for the scenario of neutron star mergers, and the significant influence of fission fragment mass distribution model on the abundance of heavy nuclei was shown. We have found that fission fragment mass distribution model is most important for fissioning nuclei with A > 260 from the region near to neutron drip-line and for superheavy nuclei. It was shown that tri-partition or ternary fission, the role of which can strongly rise in neutron rich hot dense matter, strongly affected on the abundance of heavy nuclei.

In present report we explore the appearance of light very neutron-rich clusters at high densities of collapsing stellar cores. Special attention is devoted to the superheavy hydrogen isotopes and dineutron and tetraneutron as well, which were not considered in previous studies. We have found that for light nuclei it is important to use exact information about its properties (values of spins and energies of known excited states) to obtain a reliable EoS. In our analysis we consider the influence of nuclear parameters, binding energy in first turn, on the abundances of nuclei under consideration. We discuss the domains in supernova where the light nuclei influence on the isotope abundances can have most important consequences.

There has recently been an increasing interest in a possible population of type Ia supernovae (SNe Ia) triggered by helium detonation on the surface of a massive white dwarf. In this paper, we first summarize possible observational signatures of the He detonationtriggered SNe Ia, emphasizing the new diagnostics of the He detonation mode potentially seen in the SN light within the first few days since the explosion. We then argue that observational properties of a peculiar SN Ia, MUSSES1604D as discovered by the Hyper Suprime-Cam (HSC) attached with the Subaru telescope, are best explained by the He-detonation scenario. We then discuss possible origins, including the He detonation scenario, of the diversity seen in the photometric properties of SNe Ia in the first few days. While the He detonation could reproduce observational properties of a fraction of SNe Ia showing the excessive emission in the first few days, it is likely that a bulk of them are linked to a different explosion mechanism where the early excess would arise due to an extensive mixing of ⁵⁶Ni during the explosion. A combined analysis of the very early phase observations and the maximum-phase observations will be key in mapping the diverse SN Ia zoo into different populations reflecting different progenitors and/or different explosion modes.

The first detection of gravitational waves a binary neutron star merger GW170817 by the LIGO-Virgo Collaboration has provided fundamental new insights into the astrophysical site for r-process nucleosynthesis and on the nature of dense neutron-star matter. The detected gravitational wave signal depends upon the tidal distortion of the neutron stars as they approach merger. We examine how the detected chirp depends the adopted equation of state. This places new constrains on the properties of nuclear matter. The detected evidence of heavy-element nucleosynthesis also provides insight into the nature of the r-process and the fission properties of the heaviest nuclei. Parametrically, one can divide models for the r-process into three scenarios roughly characterized by the number of neutron captures per seed nucleus (n/s). In addition to neutron-star mergers, these include magneto-hydrodynamic jets from supernovae and the neutrino heated wind above the proto neutron star in core-collapse supernovae. Insight from GW170817 allows one to better quantify the relative contributions of each astrophysical site and the fission termination of the r-process recycling.