Origin of the elements

What is the origin of the oxygen we breathe, the hydrogen and oxygen (in form of water H2O) in rivers and oceans, the carbon in all organic compounds, the silicon in electronic hardware, the calcium in our bones, the iron in steel, silver and gold in jewels, the rare earths utilized, e.g. in magnets or lasers, lead or lithium in batteries, and also of naturally occurring uranium and plutonium? The answer lies in the skies. Astrophysical environments from the Big Bang to stars and stellar explosions are the cauldrons where all these elements are made. The papers by Burbidge (Rev Mod Phys 29:547–650, 1957) and Cameron (Publ Astron Soc Pac 69:201, 1957), as well as precursors by Bethe, von Weizsäcker, Hoyle, Gamow, and Suess and Urey provided a very basic understanding of the nucleosynthesis processes responsible for their production, combined with nuclear physics input and required environment conditions such as temperature, density and the overall neutron/proton ratio in seed material. Since then a steady stream of nuclear experiments and nuclear structure theory, astrophysical models of the early universe as well as stars and stellar explosions in single and binary stellar systems has led to a deeper understanding. This involved improvements in stellar models, the composition of stellar wind ejecta, the mechanism of core-collapse supernovae as final fate of massive stars, and the transition (as a function of initial stellar mass) from core-collapse supernovae to hypernovae and long duration gamma-ray bursts (accompanied by the formation of a black hole) in case of single star progenitors. Binary stellar systems give rise to nova explosions, X-ray bursts, type Ia supernovae, neutron star, and neutron star–black hole mergers. All of these events (possibly with the exception of X-ray bursts) eject material with an abundance composition unique to the specific event and lead over time to the evolution of elemental (and isotopic) abundances in the galactic gas and their imprint on the next generation of stars. In the present review, we want to give a modern overview of the nucleosynthesis processes involved, their astrophysical sites, and their impact on the evolution of galaxies.

Unequal-mass boson-star binaries: initial data and merger dynamics

We present a generalisation of the curative initial data construction derived for equal-mass compact binaries in Helferet al(2019Phys. Rev.D99044046; 2022Class. Quantum Grav.39074001) to arbitrary mass ratios. We demonstrate how these improved initial data avoid substantial spurious artifacts in the collision dynamics of unequal-mass boson-star binaries in the same way as has previously been achieved with the simpler method restricted to the equal-mass case. We employ the improved initial data to explore in detail the impact of phase offsets in the coalescence of equal- and unequal-mass boson star binaries.

Different Types of Compactness and Their Importance in Causality

The notions of different types of compactness in a spacetime manifold has reviewed in this article. Also, their relations with Cauchy hypersurfaces, which play very important role in globally hyperbolic spacetimes has been discussed. For example, A be a closed subset of a spacetime M having a compact intersection with all the Cauchy hypersurfaces of it, then A⊂J(C) for some compact set C⊂M and conversely. Past and future compact sets in a spacetime and their interrelations with spacelike and timelike compactness are also discussed here by introducing necessary definitions, propositions, and diagrams wherever necessary, for the sake of understanding. Also, it is shown that, a closed advanced set is strictly future compact set. The relations among those compact sets themselves has been mentioned elaborately.

Anisotropic charged stellar models with modified Van der Waals EoS in f(Q) gravity

This paper is based on the study of compact stars in the context of electric fields and the nonmetricity effects of gravity. Due to this, we are motivated to build stellar models based on spherically symmetric space-time in f(Q) gravity. The space-time solution is obtained by Durgapal and Bannerji (Phys Rev D 27:328–331,1983) potential along with modified Van der Waals equation of state (EoS) $$p_r=\eta \rho ^2+ \frac{\beta \rho }{\gamma \rho +1}$$ p r = η ρ 2 + β ρ γ ρ + 1 by introducing a specific form of electric charge function $$q(r)=kr^3$$ q ( r ) = k r 3 . In order to validate our charge model, we used observational data from the literature for celestial objects like Her X-1, 4U 1538-52, SAX J1808.4-3658, and SMC X-1. Furthermore, we have also retrieved the uncharged effects of gravity for the model SMC X-1 by taking $$k=0$$ k = 0 . Our present physical analysis shows that all the obtained features for the present solution are in excellent agreement with the viable model as far as observational data is concerned.

Hidden conformal symmetry for dyonic Kerr-Sen black hole and its gauged family

Motivated by advanced progress in the holographic theory between rotating black holes and CFT, we explore the conformal invariance on dyonic Kerr-Sen black hole and its gauged family. We consider a neutral massless scalar probe on the black holes’ background within the low-frequency limit and exhibit that the solution space possesses $$SL(2,R)\times SL(2,R)$$ S L ( 2 , R ) × S L ( 2 , R ) isometry. The periodic identification of the azimuthal angle corresponds to the spontaneous conformal symmetry breaking by temperatures $$T_L,T_R$$ T L , T R . Using the computation of the central charges on Sakti and Burikham (Phys Rev D 106:106006, 2022) that we recalculate by considering the contributions of all associated fields, we successfully derive the Bekenstein-Hawking entropy from Cardy entropy formula. Furthermore, we also calculate the absorption cross-section from gravity side for generic non-extremal dyonic Kerr-Sen black hole and near-extremal gauged dyonic Kerr-Sen black hole. Our calculations show that those quantities are in a perfect match with the calculation from CFT. Therefore, our findings further support the duality between rotating black holes and CFTs.

Fundamental quantum limit for linear measurements with instability

The fundamental quantum limit, or the quantum Cramér-Rao bound, defines the sensitivity limit for quantum measurements. For linear measurement systems, such as gravitational-wave detectors, it is inversely proportional to the noise spectrum of the dynamical variable that couples to the measured signal. Defining a physically meaningful spectrum, however, requires that the system is stable and a steady state exists. We relax such a stability requirement and prove that the fundamental quantum limit can be derived simply by considering the open-loop dynamics in the Fourier domain.

Acoustic Metric and Planck Constants

Based on Akama–Diakonov (AD) theory of emergent tetrads, it was suggested that one can introduce two Planck constants, $$\hbar $$ and $$\not h$$, which are the parameters of the corresponding components of Minkowski metric, $$g_{{{\text{Mink}}}}^{{\mu \nu }}$$ = diag(−$${{\hbar }^{2}}$$, $${{\not h}^{2}}$$, $${{\not h}^{2}}$$, $${{\not h}^{2}}$$). In the Akama–Diakonov theory, the interval ds is dimensionless, as a result the metric elements and thus the Planck constants have nonzero dimensions. The Planck constant $$\hbar $$ has dimension of time, and the Planck constant $$\not h$$ has dimension of length. It is natural to compare $$\not h$$ with the Planck length lP. However, this connection remains an open question, because the microscopic (trans-Planckian) physics of the quantum vacuum is not known. Here we study this question using the effective gravity emerging for sound wave quanta (phonons) in superfluid Bose liquid, where the microscopic physics is known, and the elements of the effective acoustic metric are determined by the parameters of the Bose liquid. Since the acoustic interval is dimensionless, one may introduce the effective “acoustic Planck constants”. The acoustic Planck constant $${{\not h}_{\text{ac}}}$$ has dimension of length and is on the order of the interatomic distance. This supports the scenario in which $$\not h$$ ~ lP. We also use the acoustic metric for consideration of dependence of $$\hbar $$ on the Hubble parameter in expanding Universe.

Observable features of charged Kiselev black hole with non-commutative geometry under various accretion flow

The light passing near the black hole (BH) is deflected due to the gravitational effect, producing the BH shadow, a dark inner region that is often surrounded by a bright ring, whose optical appearance comes directly from BH’s mass and its angular momentum. We mainly study the shadow and observable features of non-commutative (NC) charged Kiselev BH, surrounded by various profiles of accretions. To obtain the BH shadow profile, we choose specific values of the model parameters and concluded that the variations of each parameter directly vary the light trajectories and size of BH. For thin disk accretion, which includes direct lensing and photon rings emissions, we analyze that the profile of BH contains the dark interior region and bright photon ring. However, their details depends upon the emissions, generally, direct emission plays significant role in the total observed luminosity, while lensing ring has a small contribution and the photon ring makes a negligible contribution, as usual, the latter can be ignored safely. Moreover, we also consider the static and infalling accretion matters and found that the location of the photon sphere is almost the same for both cases. However, the specific intensity which is observed from BH profile found to be darker for infalling accretion case due to the Doppler effect of the infalling motion as compared to the static one.

Bouncing cosmology in modified gravity with higher-order curvature terms

A bouncing scenario of a flat homogeneous and isotropic universe is explored by using the reconstruction technique for the power-law parametrization of the Hubble parameter in a modified gravity theory with higher-order curvature and trace of the energy-momentum tensor terms. It is demonstrated that bouncing criteria are satisfied so that the cosmological initial singularity can be avoided. In addition, it is shown that the equation of state parameter crosses the line of the phantom divide. In the present scenario, the universe is filled with perfect fluid around the bouncing point, in which the universe becomes highly unstable and a big bounce can be realized. Furthermore, it is found that extremal acceleration occurs at the bouncing point.

Mathematical Reflections on Locality

Starting from the principle of locality in quantum field theory, which states that an object is influenced directly only by its immediate surroundings, we review some features of the notion of locality arising in physics and mathematics. We encode these in locality relations, given by symmetric binary relations, and locality morphisms, namely maps that factorise on products of pairs in the graph of such locality relations. This factorisation is a key property in the context of renormalisation, as illustrated on the factorisation of an exponential sum on convex cones, discussed at the end of the paper. The subject of locality is so vast and the issues it raises are so subtle, that this brief and modest presentation can only offer a small glimpse into this fascinating topic.

Shielding of Penrose superradiance in optical black holes

We investigate the effect of superradiance shielding for the analogue rotating black holes simulated by optical vortices by calculating the radial motion of massless particles in such spacetime background. We add the conditions $$E<L\Omega _{r_{e}}$$ E < L Ω r e and $$L>0$$ L > 0 to judge the classically forbidden region of superradiance. It is found that the superradiance forbidden region exists near the static limit inside the ergosphere, which will limit the classical Penrose process for the particles with some specific energies and angular momenta. Once these particles satisfying the superradiance conditions are measured at the outside of the ergosphere, this shows that the Penrose process can be quantum.

Supercomputers against strong coupling in gravity with curvature and torsion

Many theories of gravity are spoiled by strongly coupled modes: the high computational cost of Hamiltonian analysis can obstruct the identification of these modes. A computer algebra implementation of the Hamiltonian constraint algorithm for curvature and torsion theories is presented. These non-Riemannian or Poincaré gauge theories suffer notoriously from strong coupling. The implementation forms a package (the ‘Hamiltonian Gauge Gravity Surveyor’ – HiGGS) for the xAct tensor manipulation suite in Mathematica. Poisson brackets can be evaluated in parallel, meaning that Hamiltonian analysis can be done on silicon, and at scale. Accordingly HiGGS is designed to survey the whole Lagrangian space with high-performance computing resources (clusters and supercomputers). To demonstrate this, the space of ‘outlawed’ Poincaré gauge theories is surveyed, in which a massive parity-even/odd vector or parity-odd tensor torsion particle accompanies the usual graviton. The survey spans possible configurations of teleparallel-style multiplier fields which might be used to kill-off the strongly coupled modes, with the results to be analysed in subsequent work. All brackets between the known primary and secondary constraints of all theories are made available for future study. Demonstrations are also given for using HiGGS – on a desktop computer – to run the Dirac–Bergmann algorithm on specific theories, such as Einstein–Cartan theory and its minimal extensions.

Ringing and echoes from black bounces surrounded by the string cloud

In the string theory, the fundamental blocks of nature are not particles but one-dimensional strings. Therefore, a generalization of this idea is to think of it as a cloud of strings. Rodrigues et al. embedded the black bounces spacetime into the string cloud, which demonstrates that the existence of the string cloud makes the Bardeen black hole singular, while the black bounces spacetime remains regular. On the other hand, the echoes are the correction to the late stage of the quasinormal ringing for a black hole, which is caused by the deviation of the spacetime relative to the initial black hole spacetime geometry in the near-horizon region. In this work, we study the gravitational wave echoes of black bounces spacetime surrounded by a cloud of strings under scalar field and electromagnetic field perturbation to explore the effects caused by a string cloud in the near-horizon region. The ringing of the regular black hole and traversable wormhole with string cloud are presented. Our results demonstrate that the black bounce spacetime with strings cloud is characterized by gravitational wave echoes as it transitions from regular black holes to wormholes, i.e. the echoes signal will facilitate us to distinguish between black holes and the wormholes in black bounces surrounded by the string cloud.

A New Perspective on Doubly Special Relativity

Doubly special relativity considers a deformation of the special relativistic kinematics parametrized by a high-energy scale, in such a way that it preserves a relativity principle. When this deformation is assumed to be applied to any interaction between particles, one faces some inconsistencies. In order to avoid them, we propose a new perspective where the deformation affects only the interactions between elementary particles. A consequence of this proposal is that the deformation cannot modify the special relativistic energy–momentum relation of a particle.

Beat-Notes Acquisition of Laser Heterodyne Interference Signal for Space Gravitational Wave Detection

In space gravitational wave detection missions, the laser heterodyne interference signal (LHI signal) has a high-dynamic characteristic due to the Doppler shift. Therefore, the three beat-notes frequencies of the LHI signal are changeable and unknown. This may further lead to the unlocking of the digital phase-locked loop (DPLL). Traditionally, fast Fourier transform (FFT) has been used as a method for frequency estimation. However, the estimation accuracy cannot meet the requirement of space missions because of the limited spectrum resolution. In order to improve the multi-frequency estimation accuracy, a method based on center of gravity (COG) is proposed. The method improves the estimation accuracy by using the amplitude of the peak points and the neighboring points of the discrete spectrum. For different windows that may be used for signal sampling, a general expression for multi-frequency correction of the windowed signal is derived. Meanwhile, a method based on error integration to reduce the acquisition error is proposed, which solves the problem of acquisition accuracy degradation caused by communication codes. The experimental results show that the multi-frequency acquisition method is able to accurately acquire the three beat-notes of the LHI signal and meet the requirement of space missions.

3D radiative transfer kilonova modelling for binary neutron star merger simulations

The detection of GW170817 and the accompanying electromagnetic counterpart, AT2017gfo, have provided an important set of observational constraints for theoretical models of neutron star mergers, nucleosynthesis, and radiative transfer for kilonovae. We apply the three-dimensional (3D) Monte Carlo radiative transfer code artis to produce synthetic light curves of the dynamical ejecta from a neutron star merger, which has been modelled with 3D smooth particle hydrodynamics and included neutrino interactions. Nucleosynthesis calculations provide the energy released from radioactive decays of r-process nuclei, and radiation transport is performed using grey opacities given as functions of the electron fraction. We present line-of-sight-dependent bolometric light curves, and find the emission along polar lines of sight to be up to a factor of ∼2 brighter than that along equatorial lines of sight. Instead of a distinct emission peak, our bolometric light curve exhibits a monotonic decline, characterized by a shoulder at the time when the bulk ejecta becomes optically thin. We show approximate band light curves based on radiation temperatures and compare these to the observations of AT2017gfo. We find that the rapidly declining temperatures lead to a blue to red colour evolution similar to that shown by AT2017gfo. We also investigate the impact of an additional, spherically symmetric secular ejecta component, and we find that the early light curve remains nearly unaffected, while after about $1\,$ d the emission is strongly enhanced and dominated by the secular ejecta, leading to the shift of the shoulder from ∼1–2 to 6–10 d.

N3LO quadratic-in-spin interactions for generic compact binaries

We derive the third subleading (N3LO) corrections of the quadratic-in-spin sectors via the EFT of spinning objects in post-Newtonian (PN) gravity. These corrections consist of contributions from 4 sectors for generic compact binaries, that enter at the fifth PN order. One of these contributions is due to a new tidal interaction, that is unique to the sectors with spin, and complements the first tidal interaction that also enters at this PN order in the simple point-mass sector. The evaluation of Feynman graphs is carried out in a generic dimension via advanced multi-loop methods, and gives rise to dimensional-regularization poles in conjunction with logarithms. At these higher-spin sectors the reduction of generalized Lagrangians entails redefinitions of the position beyond linear order. We provide here the most general Lagrangians and Hamiltonians. We then specify the latter to simplified configurations, and derive the consequent gauge-invariant relations among the binding energy, angular momentum, and frequency. We end with a derivation of all the scattering angles that correspond to an extension of our Hamiltonians to the scattering problem in the simplified aligned-spins configuration, as a guide to scattering-amplitudes studies.

Astrophysics with the Laser Interferometer Space Antenna

The Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy, and, as such, it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and space-born instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA’s first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed; ultra-compact stellar-mass binaries, massive black hole binaries, and extreme or interme-diate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help making progress in the different areas. New research avenues that LISA itself, or its joint exploitation with upcoming studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe.

Kantowski–Sachs cosmology in scalar-torsion theory

In the context of scalar-torsion theory we investigate the evolution of the cosmological anisotropies for a Kantowski–Sachs background geometry. We study the phase-space of the gravitational field equations by determining the admitted stationary points and study their stability properties. For the potential function of the non-minimally coupled scalar field we assume the exponential and the power-law functions. Finally, we make use of Poincare variables in order to investigate the existence of stationary points at the infinity regime of the dynamics.

Gradient flow of Einstein-Maxwell theory and Reissner-Nordström black holes

Ricci flow is a natural gradient flow of the Einstein-Hilbert action. Here we consider the analog for the Einstein-Maxwell action, which gives Ricci flow with a stress tensor contribution coupled to a Yang-Mills flow for the Maxwell field. We argue that this flow is well-posed for static spacetimes with pure electric or magnetic potentials and show it preserves both non-extremal and extremal black hole horizons. In the latter case we find the flow of the near horizon geometry decouples from that of the exterior. The Schwarzschild black hole is an unstable fixed point of Ricci flow for static spacetimes. Here we consider flows of the Reissner-Nordström (RN) fixed point. The magnetic RN solution becomes a stable fixed point of the flow for sufficient charge. However we find that the electric RN black hole is always unstable. Numerically solving the flow starting with a spherically symmetric perturbation of a non-extremal RN solution, we find similar behaviour in the electric case to the Ricci flows of perturbed Schwarzschild, namely the horizon shrinks to a singularity in finite time or expands forever. In the magnetic case, a perturbed unstable RN solution has a similar expanding behaviour, but a perturbation that decreases the horizon size flows to a stable black hole solution rather than a singularity. For extremal RN we solve the near horizon flow for spherical symmetry exactly, and see in the electric case two unstable directions which flow to singularities in finite flow time. However, even turning these off, and fixing the near horizon geometry to be that of RN, we numerically show that the flows appear to become singular in the vicinity of its horizon.