Big Bang nucleosynthesis(BBN)theory predicts the primordial abundances of the light elements^(2) H(referred to as deuterium,or D for short),^(3)He,^(4)He,and^(7) Li produced in the early universe.Among these,deuterium...Big Bang nucleosynthesis(BBN)theory predicts the primordial abundances of the light elements^(2) H(referred to as deuterium,or D for short),^(3)He,^(4)He,and^(7) Li produced in the early universe.Among these,deuterium,the first nuclide produced by BBN,is a key primordial material for subsequent reactions.To date,the uncertainty in predicted deuterium abundance(D/H)remains larger than the observational precision.In this study,the Monte Carlo simulation code PRIMAT was used to investigate the sensitivity of 11 important BBN reactions to deuterium abundance.We found that the reaction rate uncertainties of the four reactions d(d,n)^(3)He,d(d,p)t,d(p,γ)^(3)He,and p(n,γ)d had the largest influence on the calculated D/H uncertainty.Currently,the calculated D/H uncertainty cannot reach observational precision even with the recent LUNA precise d(p,γ)^(3) He rate.From the nuclear physics aspect,there is still room to largely reduce the reaction-rate uncertainties;hence,further measurements of the important reactions involved in BBN are still necessary.A photodisintegration experiment will be conducted at the Shanghai Laser Electron Gamma Source Facility to precisely study the deuterium production reaction of p(n,γ)d.展开更多
In our original paper, we outlined a new model of nucleosynthesis which began when a small percentage of the vacuum energy was converted primarily into neutron-antineutron pairs but with a very small excess of neutron...In our original paper, we outlined a new model of nucleosynthesis which began when a small percentage of the vacuum energy was converted primarily into neutron-antineutron pairs but with a very small excess of neutrons. In this paper, we present a detailed study of that original idea. We show that immediately after their inception, annihilation and charge exchange reactions proceeded at a very high rate and after an interval of no more than 10<sup>-12</sup> s, the matter/antimatter asymmetry of the universe and the present-day abundance of baryons had been established. The annihilations produced the high density of leptons critical for the weak interactions and the photons that make up the CMB. The model predicts a photon temperature in agreement with the present-day CMB value and also explains the origin of the CMB anisotropy spectrum. We also show how the nucleosynthesis density variations needed to explain all cosmic structures can resolve the difficulties that arise when trying to explain observed primordial element abundances in terms of a single-density universal model of nucleosynthesis.展开更多
We investigate nucleosynthesis inside the gamma-ray burst （GRB） accre- tion disks formed by the Type II collapsars. In these collapsars, the core collapse of massive stars first leads to the formation of a proto-neu...We investigate nucleosynthesis inside the gamma-ray burst （GRB） accre- tion disks formed by the Type II collapsars. In these collapsars, the core collapse of massive stars first leads to the formation of a proto-neutron star. After that, an out- ward moving shock triggers a successful supernova. However, the supernova ejecta lacks momentum and within a few seconds the newly formed neutron star gets trans- formed to a stellar mass black hole via massive fallback. The hydrodynamics of such an accretion disk formed from the fallback material of the supernova ejecta has been studied extensively in the past. We use these well-established hydrodynamic models for our accretion disk in order to understand nucleosynthesis, which is mainly ad- vection dominated in the outer regions. Neutrino cooling becomes important in the inner disk where the temperature and density are higher. The higher the accretion rate （M） is, the higher the density and temperature are in the disks. We deal with accre- tion disks with relatively low accretion rates： 0.001 Mo s-1 ~ 3）/~ 0.01 Mo S--1 and hence these disks are predominantly advection dominated. We use He-rich and Si- rich abundances as the initial condition of nucleosynthesis at the outer disk, and being equipped with the disk hydrodynamics and the nuclear network code, we study the abundance evolution as matter inflows and falls into the central object. We investigate the variation in the nucleosynthesis products in the disk with the change in the initial abundance at the outer disk and also with the change in the mass accretion rate. We report the synthesis of several unusual nuclei like 31p, 39K, 43Sc＇ 35C1 and various isotopes of titanium, vanadium, chromium, manganese and copper. We also confirm that isotopes of iron, cobalt, nickel, argon, calcium, sulphur and silicon get synthe- sized in the disk, as shown by previous authors. Much of these heavy elements thus synthesized are ejected from the disk via outflows and hence they should leave their signature in observed data.展开更多
We study the finite temperature and density effects on beta decay rates to compute their contributions to nucleosynthesis. QED type corrections to beta decay from the hot and dense background are estimated in terms of...We study the finite temperature and density effects on beta decay rates to compute their contributions to nucleosynthesis. QED type corrections to beta decay from the hot and dense background are estimated in terms of the statistical corrections to the self-mass of an electron. For this purpose, we re-examine the hot and dense background contributions to the electron mass and compute its effect to the beta decay rate, helium yield, energy density of the universe as well as the change in neutrino temperature from the first order contribution to the self-mass of electrons during these processes. We explicitly show that the thermal contribution to the helium abundance at T = m of a cooling universe (0.045 percent) is higher than the corresponding contribution to helium abundance of a heating universe (0.031 percent) due to the existence of hot fermions before the beginning of nucleosynthesis and their absence after the nucleosynthesis, in the early universe. Thermal contribution to helium abundance was a simple quadratic function of temperature, before and after the nucleosynthesis. However, this quadratic behavior was not the same before the decoupling temperature due to weak interactions;so the nucleosynthesis did not even start before the universe had cooled down to the neutrino decoupling temperatures and QED became a dominant theory in the presence of a high concentration of charged fermions. It is also explicitly shown that the chemical potential in the core of supermassive and superdense stars affect beta decay and their helium abundance but the background contributions depend on the ratio between temperature and chemical potential and not the chemical potential or temperature only. We calculate the hot and dense background contributions for m = T = μ. It has been noticed that temperature plays a role in regulating parameter in an extremely dense systems. Therefore, for extremely dense systems, temperature has to be large enough to get the expected value of helium production in the stellar cores.展开更多
Nucleosynthesis in advection-dominated accretion flow （ADAF） onto a black hole is proposed to be an important role in chemical evolution around compact stars. We investigate the nucleosynthesis in ADAF relevant for ...Nucleosynthesis in advection-dominated accretion flow （ADAF） onto a black hole is proposed to be an important role in chemical evolution around compact stars. We investigate the nucleosynthesis in ADAF relevant for a black hole of low mass, different from that of the self-similar solution. In particular, the presence of supersolar metal mass fractions of some isotopes seems to be associated with the known black hole nucleosynthesis in ADAF, which offers further evidence of diversity of the chemical enrichment.展开更多
The Carmeli Cosmological Special Relativity theory (CSR) is used to study the universe at early times after the big bang. The universe temperature vs. time relation is developed from the mass density relation. It is s...The Carmeli Cosmological Special Relativity theory (CSR) is used to study the universe at early times after the big bang. The universe temperature vs. time relation is developed from the mass density relation. It is shown that CSR is well suited to analyze the nucleosynthesis of the light elements up to beryllium, equivalent to the standard model.展开更多
During the past few decades, it has become clear that the distribution, sizes, and masses of cosmic structures are best described as fractal rather than homogeneous. This means that an entirely different formalism is ...During the past few decades, it has become clear that the distribution, sizes, and masses of cosmic structures are best described as fractal rather than homogeneous. This means that an entirely different formalism is needed to replace the standard perturbation model of structure formation. Recently, we have been developing a model of cosmology that accounts for a large number of the observed properties of the universe. A key component of this model is that fractal structures that later regulated the creation of both matter and radiation came into existence during the initial Planck-era inflation. Initially, the vacuum was the only existence and since time, distance, and energy were uncertain, its only property, the curvature (or energy), was most likely distributed randomly. Everything that happened after the Planck era can be described by the known laws of physics so the remaining fundamental problem is to discover how such a random beginning could organize itself into the hierarchy of highly non-random self-similar structures on all length scales that are necessary to explain the existence of all cosmic structures. In this paper, we present a variation of the standard sandpile model that points to a solution. Incidental to our review of the distributions of cosmic structures, we discovered that the apparent transition from a fractal to a homogeneous distribution of structures at a distance of about 150 Mpc is a consequence of the finite size of the universe rather than a change in the underlying statistics of the distributions.展开更多
Within the context of the proton-neutron quasi-particle random phase approximation(pn-QRPA)model and TALYS v1.96 code,the radiative capture(^(99)Tc(n,γ)^(100)Tc)and stellar weak interaction(^(99)Tc→^(99)Ru+e^(−)+ν_...Within the context of the proton-neutron quasi-particle random phase approximation(pn-QRPA)model and TALYS v1.96 code,the radiative capture(^(99)Tc(n,γ)^(100)Tc)and stellar weak interaction(^(99)Tc→^(99)Ru+e^(−)+ν_(e))rates were computed during thermal pulses operating in asymptotic giant branch stars.The Maxwellian average cross-section(MACS)and neutron capture rates for the^(99)Tc(n,γ)^(100)Tc process are analyzed within the context of statistical code TALYS v1.96.The effect of nuclear level density(NLD)andγ-strength functions on MACS and neutron capture rates has been examined.The model-based computations for MACS provided an insightful contrast to prior investigated findings.The sensitivity of stellar weak interaction rates to different densities and temperatures is investigated using the pn-QRPA model.The impact of thermally populated excited states on electron emission(β^(−))rates in^(99)Tc is extensively examined.Additionally,a comparison is made between the study of the stellarβ^(−)decay rates and the thermal neutron capture rates.It is found that at T_(9)=0.26 the thermal neutron capture rates(λ_((n,γ)))and the temperature dependent stellarβ^(−)decay rates( λ_(β-))cross each other.However,at higher temperatures,theλ(n,γ)are found to be higher than λ_(β-).展开更多
Object LAMOST J020623.21+494127.9(program star) in the thin disk of the Milky Way is reported as a highly r-process-enhanced r-II star with [Eu/Fe] = +1.32 and [Fe/H] =-0.54. The chemical profile of the star reflects ...Object LAMOST J020623.21+494127.9(program star) in the thin disk of the Milky Way is reported as a highly r-process-enhanced r-II star with [Eu/Fe] = +1.32 and [Fe/H] =-0.54. The chemical profile of the star reflects the intrinsic composition of the gas cloud present at its birth. Using an abundance decomposition method, we fit25 elements from the abundance data set, including 10 heavy neutron-capture elements. We explore the astrophysical origin of the elements in this star through its abundance ratios and component ratios. We find that the contributions from the massive stars played a significant role in the production of light elements in the program star. Our analysis reveals that the heavy neutron-capture elements are produced purely by the main r-process. However, the adopted main r-process model does not adequately fit the observed data, suggesting another main r-process pattern may exist.展开更多
A kilonova is an optical-infrared transient powered by the radioactive decay of heavy nuclei from a binary neutron star merger.Its observational characteristics depend on the mass and the nuclide composition of merger...A kilonova is an optical-infrared transient powered by the radioactive decay of heavy nuclei from a binary neutron star merger.Its observational characteristics depend on the mass and the nuclide composition of merger ejecta,which are sensitive to the equation of state(EoS)of the neutron star.We use astrophysical conditions derived from different EoSs as nucleosynthesis inputs to explore the impact of various EoS on the r-process nucleosynthesis and the kilonova emission.Our results show that both the abundance patterns of merger ejecta and kilonova light curves are strongly dependent on the neutron star EoSs.Given the mass of two neutron stars,the merger with a softer EoS tends to generate a larger amount of ejected material,and may lead to a brighter kilonova peak luminosity.The relationship between the neutron star EoS and the peak luminosity provides a probe for constraining the properties of EoS in multi-messenger observations of neutron star mergers.展开更多
基金supported by the National Key R&D Program of China(No.2022YFA1602401)by the National Natural Science Foundation of China(No.11825504)。
文摘Big Bang nucleosynthesis(BBN)theory predicts the primordial abundances of the light elements^(2) H(referred to as deuterium,or D for short),^(3)He,^(4)He,and^(7) Li produced in the early universe.Among these,deuterium,the first nuclide produced by BBN,is a key primordial material for subsequent reactions.To date,the uncertainty in predicted deuterium abundance(D/H)remains larger than the observational precision.In this study,the Monte Carlo simulation code PRIMAT was used to investigate the sensitivity of 11 important BBN reactions to deuterium abundance.We found that the reaction rate uncertainties of the four reactions d(d,n)^(3)He,d(d,p)t,d(p,γ)^(3)He,and p(n,γ)d had the largest influence on the calculated D/H uncertainty.Currently,the calculated D/H uncertainty cannot reach observational precision even with the recent LUNA precise d(p,γ)^(3) He rate.From the nuclear physics aspect,there is still room to largely reduce the reaction-rate uncertainties;hence,further measurements of the important reactions involved in BBN are still necessary.A photodisintegration experiment will be conducted at the Shanghai Laser Electron Gamma Source Facility to precisely study the deuterium production reaction of p(n,γ)d.
文摘In our original paper, we outlined a new model of nucleosynthesis which began when a small percentage of the vacuum energy was converted primarily into neutron-antineutron pairs but with a very small excess of neutrons. In this paper, we present a detailed study of that original idea. We show that immediately after their inception, annihilation and charge exchange reactions proceeded at a very high rate and after an interval of no more than 10<sup>-12</sup> s, the matter/antimatter asymmetry of the universe and the present-day abundance of baryons had been established. The annihilations produced the high density of leptons critical for the weak interactions and the photons that make up the CMB. The model predicts a photon temperature in agreement with the present-day CMB value and also explains the origin of the CMB anisotropy spectrum. We also show how the nucleosynthesis density variations needed to explain all cosmic structures can resolve the difficulties that arise when trying to explain observed primordial element abundances in terms of a single-density universal model of nucleosynthesis.
基金partly supported by the ISRO grant ISRO/RES/2/367/10-11
文摘We investigate nucleosynthesis inside the gamma-ray burst （GRB） accre- tion disks formed by the Type II collapsars. In these collapsars, the core collapse of massive stars first leads to the formation of a proto-neutron star. After that, an out- ward moving shock triggers a successful supernova. However, the supernova ejecta lacks momentum and within a few seconds the newly formed neutron star gets trans- formed to a stellar mass black hole via massive fallback. The hydrodynamics of such an accretion disk formed from the fallback material of the supernova ejecta has been studied extensively in the past. We use these well-established hydrodynamic models for our accretion disk in order to understand nucleosynthesis, which is mainly ad- vection dominated in the outer regions. Neutrino cooling becomes important in the inner disk where the temperature and density are higher. The higher the accretion rate （M） is, the higher the density and temperature are in the disks. We deal with accre- tion disks with relatively low accretion rates： 0.001 Mo s-1 ~ 3）/~ 0.01 Mo S--1 and hence these disks are predominantly advection dominated. We use He-rich and Si- rich abundances as the initial condition of nucleosynthesis at the outer disk, and being equipped with the disk hydrodynamics and the nuclear network code, we study the abundance evolution as matter inflows and falls into the central object. We investigate the variation in the nucleosynthesis products in the disk with the change in the initial abundance at the outer disk and also with the change in the mass accretion rate. We report the synthesis of several unusual nuclei like 31p, 39K, 43Sc＇ 35C1 and various isotopes of titanium, vanadium, chromium, manganese and copper. We also confirm that isotopes of iron, cobalt, nickel, argon, calcium, sulphur and silicon get synthe- sized in the disk, as shown by previous authors. Much of these heavy elements thus synthesized are ejected from the disk via outflows and hence they should leave their signature in observed data.
文摘We study the finite temperature and density effects on beta decay rates to compute their contributions to nucleosynthesis. QED type corrections to beta decay from the hot and dense background are estimated in terms of the statistical corrections to the self-mass of an electron. For this purpose, we re-examine the hot and dense background contributions to the electron mass and compute its effect to the beta decay rate, helium yield, energy density of the universe as well as the change in neutrino temperature from the first order contribution to the self-mass of electrons during these processes. We explicitly show that the thermal contribution to the helium abundance at T = m of a cooling universe (0.045 percent) is higher than the corresponding contribution to helium abundance of a heating universe (0.031 percent) due to the existence of hot fermions before the beginning of nucleosynthesis and their absence after the nucleosynthesis, in the early universe. Thermal contribution to helium abundance was a simple quadratic function of temperature, before and after the nucleosynthesis. However, this quadratic behavior was not the same before the decoupling temperature due to weak interactions;so the nucleosynthesis did not even start before the universe had cooled down to the neutrino decoupling temperatures and QED became a dominant theory in the presence of a high concentration of charged fermions. It is also explicitly shown that the chemical potential in the core of supermassive and superdense stars affect beta decay and their helium abundance but the background contributions depend on the ratio between temperature and chemical potential and not the chemical potential or temperature only. We calculate the hot and dense background contributions for m = T = μ. It has been noticed that temperature plays a role in regulating parameter in an extremely dense systems. Therefore, for extremely dense systems, temperature has to be large enough to get the expected value of helium production in the stellar cores.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11547041,11403007,11673007,11643007,11333004,U1531130,11673059,11390374 and 11521303the Chinese Academy of Sciences under Grant Nos KJZD-EW-M06-01and QYZDB-SSW-SYS001
文摘Nucleosynthesis in advection-dominated accretion flow （ADAF） onto a black hole is proposed to be an important role in chemical evolution around compact stars. We investigate the nucleosynthesis in ADAF relevant for a black hole of low mass, different from that of the self-similar solution. In particular, the presence of supersolar metal mass fractions of some isotopes seems to be associated with the known black hole nucleosynthesis in ADAF, which offers further evidence of diversity of the chemical enrichment.
文摘The Carmeli Cosmological Special Relativity theory (CSR) is used to study the universe at early times after the big bang. The universe temperature vs. time relation is developed from the mass density relation. It is shown that CSR is well suited to analyze the nucleosynthesis of the light elements up to beryllium, equivalent to the standard model.
文摘During the past few decades, it has become clear that the distribution, sizes, and masses of cosmic structures are best described as fractal rather than homogeneous. This means that an entirely different formalism is needed to replace the standard perturbation model of structure formation. Recently, we have been developing a model of cosmology that accounts for a large number of the observed properties of the universe. A key component of this model is that fractal structures that later regulated the creation of both matter and radiation came into existence during the initial Planck-era inflation. Initially, the vacuum was the only existence and since time, distance, and energy were uncertain, its only property, the curvature (or energy), was most likely distributed randomly. Everything that happened after the Planck era can be described by the known laws of physics so the remaining fundamental problem is to discover how such a random beginning could organize itself into the hierarchy of highly non-random self-similar structures on all length scales that are necessary to explain the existence of all cosmic structures. In this paper, we present a variation of the standard sandpile model that points to a solution. Incidental to our review of the distributions of cosmic structures, we discovered that the apparent transition from a fractal to a homogeneous distribution of structures at a distance of about 150 Mpc is a consequence of the finite size of the universe rather than a change in the underlying statistics of the distributions.
基金the financial support of the Higher Education Commission Pakistan through project number 20-15394/NRPU/R&D/HEC/2021.
文摘Within the context of the proton-neutron quasi-particle random phase approximation(pn-QRPA)model and TALYS v1.96 code,the radiative capture(^(99)Tc(n,γ)^(100)Tc)and stellar weak interaction(^(99)Tc→^(99)Ru+e^(−)+ν_(e))rates were computed during thermal pulses operating in asymptotic giant branch stars.The Maxwellian average cross-section(MACS)and neutron capture rates for the^(99)Tc(n,γ)^(100)Tc process are analyzed within the context of statistical code TALYS v1.96.The effect of nuclear level density(NLD)andγ-strength functions on MACS and neutron capture rates has been examined.The model-based computations for MACS provided an insightful contrast to prior investigated findings.The sensitivity of stellar weak interaction rates to different densities and temperatures is investigated using the pn-QRPA model.The impact of thermally populated excited states on electron emission(β^(−))rates in^(99)Tc is extensively examined.Additionally,a comparison is made between the study of the stellarβ^(−)decay rates and the thermal neutron capture rates.It is found that at T_(9)=0.26 the thermal neutron capture rates(λ_((n,γ)))and the temperature dependent stellarβ^(−)decay rates( λ_(β-))cross each other.However,at higher temperatures,theλ(n,γ)are found to be higher than λ_(β-).
基金supported by the National Key Basic R&D Program of China No. 2024YFA1611903the National Natural Science Foundation of China (NSFC, Grant No. 12173013)+2 种基金the project of Hebei provincial department of science and technology under the grant No. 226Z7604Gthe Hebei NSF (No. A2021205006)the China Manned Space Project for funding support of this study
文摘Object LAMOST J020623.21+494127.9(program star) in the thin disk of the Milky Way is reported as a highly r-process-enhanced r-II star with [Eu/Fe] = +1.32 and [Fe/H] =-0.54. The chemical profile of the star reflects the intrinsic composition of the gas cloud present at its birth. Using an abundance decomposition method, we fit25 elements from the abundance data set, including 10 heavy neutron-capture elements. We explore the astrophysical origin of the elements in this star through its abundance ratios and component ratios. We find that the contributions from the massive stars played a significant role in the production of light elements in the program star. Our analysis reveals that the heavy neutron-capture elements are produced purely by the main r-process. However, the adopted main r-process model does not adequately fit the observed data, suggesting another main r-process pattern may exist.
基金supported by the National Natural Science Foundation of China(NSFC,grant Nos.12403043,12347172,and 12133003)M.H.C.also acknowledges support from the China Postdoctoral Science Foundation(grant Nos.GZB20230029 and 2024M750057)supported by the Guangxi Talent Program(Highland of Innovation Talents).
文摘A kilonova is an optical-infrared transient powered by the radioactive decay of heavy nuclei from a binary neutron star merger.Its observational characteristics depend on the mass and the nuclide composition of merger ejecta,which are sensitive to the equation of state(EoS)of the neutron star.We use astrophysical conditions derived from different EoSs as nucleosynthesis inputs to explore the impact of various EoS on the r-process nucleosynthesis and the kilonova emission.Our results show that both the abundance patterns of merger ejecta and kilonova light curves are strongly dependent on the neutron star EoSs.Given the mass of two neutron stars,the merger with a softer EoS tends to generate a larger amount of ejected material,and may lead to a brighter kilonova peak luminosity.The relationship between the neutron star EoS and the peak luminosity provides a probe for constraining the properties of EoS in multi-messenger observations of neutron star mergers.
