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In recent years, the formation and evolution of rapidly accreting supermassive stars has received significant attention in the hope of better understanding the origin of high redshift quasars. It is often taken for granted that once formed, these supermassive stars will encounter the general relativistic radial instability and collapse to form massive black holes. Here, we present the first ever general relativistic hydrodynamical simulations of the collapse of rapidly accreting supermassive stars. We find that black hole formation is in many cases prevented by nuclear burning due to the long timescales of the collapse of these stars ($10^6$ s). Consequently, this is a novel astrophysical site for hot CNO burning and hydrogen burning via proton captures. For Pop III accreting supermassive stars, we find that only stars with very high (100 $\rm{M_\odot}/$yr) or low (0.1 $\rm{M_\odot}/$yr) accretion rates can form black holes, with models in between undergoing energetic thermonuclear pulsations. The final fate of these pulsating models may be to undergo subsequent pulsations or explosions or to collapse to black holes. For metal rich accreting supermassive stars ($Z\geq 0.1 \rm{Z_\odot}$), we do not find any black hole formation, with some models undergoing extremely energetic explosions ($10^{55}$ ergs). Our results invite further study on the formation of massive black holes from rapidly accreting supermassive stars which have reached the general relativistic radial instability., Comment: Accepted to PRD

SN2018ibb is a recently observed hydrogen poor super-luminous supernova which appears to be powered by the decay of $30\;\rm{M_\odot}$ of radioactive nickel. This supernova has been suggested to show hybrid signatures of a pair instability supernova and an interacting supernova. In a previous paper, we found that rotating, metal enriched pair instability supernova progenitors appeared to check both of these boxes. In this paper, we model the lightcurves of the pair instability supernovae using STELLA. We find that the STELLA models can explain the overall shape of the bolometric lightcurve of SN2018ibb, though not specific morphological features such as the luminosity peak or the bump at roughly three hundred days after the peak. We also estimate the contribution from interaction, and find that with relatively low wind velocities, the circum-stellar medium originating from the stellar winds is consistent with the evidence for interaction in the spectra. The observed values of the photosphere velocity in the hundred days after peak luminosity are similar to the STELLA models, but the deceleration is lower. This leads to the biggest inconsistency which is the black body temperature of SN2018ibb being much hotter than any of the STELLA models. We note that this high temperature (and the flat velocity) may be difficult to reconcile with the long rise time of SN2018ibb, but nevertheless conclude that if it is accurate, this discrepancy represents a challenge for SN2018ibb being a robust PISN candidate. This result is noteworthy given the lack of other scenarios for this supernova., Comment: Accepted to APJ

In this paper we revisit metal-enriched rotating pair instability supernovae (PISNe) models for metallicities consistent with the Small Magellanic Cloud (SMC), the Large Magellanic Cloud (LMC) and 0.1$Z_\odot$. By calculating multiple models, we intend to clarify mass ranges and the ejected $^{56}$Ni masses from the PISNe, and mass loss histories for progenitors. We find the choice of the Wolf-Rayet (WR) mass-loss rates are important and we adopt the recently proposed rate of Sander & Vink (2020), which covers the mass ranges for PISNe progenitors. We show that slow rotation lowers the PISN range due to the increase in core mass by rotational mixing. On the other hand, if we assume typical rotation speed for observed OB stars, the mass loss increase becomes more significant and the final stellar masses are smaller than non-rotating models. As a result, typical mass range for bright SNe, with $^{56}$Ni mass more than 10${ M}_\odot$ for such fast rotating models are more than 400, 350 ${ M}_\odot$, for LMC and 0.1$Z_\odot$ metallicities, respectively. It is interesting that, unlike previous works, we find Oxygen rich progenitors for most cases. This O-rich progenitor may be consistent with the recently identified PISN candidate SN2018ibb. He-rich progenitors are seen only for relatively dim and metal poor ($Z \lesssim 0.1 Z_\odot$) PISNe. We also discuss the black hole mass gap for metal-enriched PISNe, and show that the upperbound for the gap is lower than in the Pop III case.

GN-z11 is an unusually luminous high redshift galaxy which was recently observed to have strong nitrogen lines while at the same time lacking traditional signatures of AGN activity. These observations have been interpreted as a super-solar nitrogen abundance which is challenging to explain with standard stellar evolution and supernovae enrichment. We present simulations of four models of metal enriched supermassive stars after the zero age main sequence which produce super-solar nitrogen consistent with the observations of GN-z11. We then show that the most massive model ends its life in a violent explosion which results in even greater nitrogen pollution., Comment: Accepted to APJL

The assembly of supermassive black holes poses a challenge primarily because of observed quasars at high redshift, but additionally because of the current lack of observations of intermediate mass black holes. One plausible scenario for creating supermassive black holes is direct collapse triggered by the merger of two gas rich galaxies. This scenario allows the creation of supermassive stars with solar metallicity, where the enhanced metallicity is enabled by extremely rapid accretion. We investigate the behavior of metal enriched supermassive stars which collapse due to the general relativistic radial instability during hydrogen burning. These stars contain both hydrogen and metals and thus may explode due to the CNO cycle (carbon-nitrogen-oxygen) and the rp process (rapid proton capture). We perform a suite of stellar evolution simulations for a range of masses and metallicities, both including and neglecting mass loss. We evaluate the stability of these supermassive stars by solving the pulsation equation in general relativity. When the stars becomes unstable, we perform 1D general relativistic hydrodynamical simulations coupled to a 153 isotope nuclear network with cooling from neutrino reactions, in order to determine if the stars explode. If the stars do explode, we post process the nucleosynthesis using a 514 isotope network which includes additional proton rich isotopes. These explosions are characterized by enhanced nitrogen and intermediate mass elements ($16\geq\rm{A}\geq25$), and suppressed light elements ($8\geq\rm{A}\geq14$), and we comment on recent observations of super-solar nitrogen in GN-z11.

The conditions under which galactic nuclear regions become active are largely unknown, although it has been hypothesized that secular processes related to galaxy morphology could play a significant role. We investigate this question using optical i-band images of 3096 SDSS quasars and galaxies at 0.3

The origin of high-redshift quasars and their supermassive black hole engines is unclear. One promising solution is the collapse of a primordial supermassive star. Observational confirmation of this scenario may be challenging, but a general relativistic instability supernova provides one avenue for such. Previous studies have found that a general relativistic instability supernova has a potentially decades-long plateau phase visible to JWST at high redshift. In this work, we examine stars with mass just below the general relativistic instability supernova mass range. These stars pulsate, ejecting a portion of their envelopes. They then contract quasi-statically back to an equilibrium temperature, at which point they again become unstable and pulsate once more. Because each pulse consumes a small amount of the available nuclear fuel, there exists the possibility of multiple pulsations. We present simulations of the contracting phase, the pulsation, and the light-curve phase. We find that the lower mass pulsating models are even brighter than the higher mass supernovae because the pulsations occur in the late helium burning phase when the stars have extremely large radii. The fact that the pulsations are more luminous and occur in a wider mass range than the supernovae bodes well for observation.

Observed supermassive black holes in the early universe have several proposed formation channels, in part because most of these channels are difficult to probe. One of the more promising channels, the direct collapse of a supermassive star, has several possible probes including the explosion of a helium-core supermassive star triggered by a general relativistic instability. We develop a straightforward method for evaluating the general relativistic radial instability without simplifying assumptions and apply it to population III supermassive stars taken from a post Newtonian stellar evolution code. This method is more accurate than previous determinations and it finds that the instability occurs earlier in the evolutionary life of the star. Using the results of the stability analysis, we perform 1D general relativistic hydrodynamical simulations and we find two general relativistic instability supernovae fueled by alpha capture reactions as well as several lower mass pulsations, analogous to the puslational pair instability process. The mass range for the events (2.6-3.0 $\times 10^4$ ${\rm M}_\odot$) is lower than had been suggested by previous works (5.5 $\times 10^4$ ${\rm M}_\odot$) because the instability occurs earlier in the star's evolution. The explosion may be visible to, among others, JWST, while the discovery of the pulsations opens up additional possibilities for observation.

Relative phases of atomic above-threshold ionization wavepackets have been investigated in a recent experiment [L. J. Zipp, A. Natan, and P. H. Bucksbaum, Optica \textbf{1}, 361-364 (2014)] exploiting interferences between different pathways in a weak probe field at half the frequency of the strong ionization pulse. In this work we theoretically explore the extraction of phase delays and time delays of attosecond wavepackets formed in strong-field ionization. We perform simulations solving the time-dependent Schr\"odinger equation and compare these results with the strong-field and Coulomb-Volkov approximations. In order to disentangle short- from long- ranged effects of the atomic potential we also perform simulations for atomic model potentials featuring a Yukawa-type short-range potential. We find significant deviations of the \textit{ab-initio} phase delays between different photoelectron pathways from the predictions by the strong-field approximation even at energies well above the ionization threshold. We identify similarities but also profound differences to the well-known interferometric extraction of phase- and time delays in one-photon ionization., Comment: 27 pages, 8 figures

We calculate the neutrino signal from Population III supermassive star collapse using a neutrino transfer code originally developed for core collapse supernovae and massive star collapse. Using this code, we are able to investigate the supermassive star mass range thought to undergo neutrino trapping ($\sim 10^4$ M$_\odot$), a mass range which has been neglected by previous works because of the difficulty of neutrino transfer. For models in this mass range, we observe a neutrino-sphere with a large radius and low density compared to typical massive star neutrino-spheres. We calculate the neutrino light-curve emitted from this neutrino-sphere. The resulting neutrino luminosity is significantly lower than the results of a previous analytical model. We briefly discuss the possibility of detecting a neutrino burst from a supermassive star or the neutrino background from many supermassive stars and conclude that the former is unlikely with current technology, unless the SMS collapse is located as close as 1 Mpc, while the latter is also unlikely even under very generous assumptions. However, the supermassive star neutrino background is still of interest as it may serve as a source of noise in proposed dark matter direct detection experiments.

Since the discovery of GW190521, several proposals have been put forward to explain the formation of a black hole in the mass gap caused by (pulsational) pair-instability, $M = 65-130 M_\odot$. We calculate the mass ejection of Pop III stars by the pulsational pair-instability (PPI) process using a stellar evolution and hydrodynamical code. If a relatively small, but reasonable value is adopted for the overshooting parameter, the stars do not become red super giants during the PPI phase. We show that in this case most of the hydrogen envelope remains after the mass ejection by PPI. We find that the BH mass could be at most $M = 109 M_\odot$ below the mass range of pair-instability supernovae.

We study quantum decoherence numerically in a system consisting of a relativistic quantum field theory coupled to a measuring device that is itself coupled to an environment. The measuring device and environment are treated as quantum, non-relativistic particles. We solve the Schr\"odinger equation for the wave function of this tripartite system using exact diagonalization. Although computational limitations on the size of the Hilbert space prevent us from exploring the regime where the device and environment consist of a truly macroscopic number of degrees of freedom, we nevertheless see clear evidence of decoherence: after tracing out the environment, the density matrix describing the system and measuring device evolves quickly towards a matrix that is close to diagonal in a subspace of pointer states., Comment: 11+3 pages

We investigate the possibility of a supernova in supermassive ($5 \times 10^4 \;M_\odot$) population III stars induced by a general relativistic instability occurring in the helium burning phase. This explosion could occur via rapid helium burning during an early contraction of the isentropic core. Such an explosion would be visible to future telescopes and could disrupt the proposed direct collapse formation channel for early universe supermassive black holes. We simulate first the stellar evolution from hydrogen burning using a 1D stellar evolution code with a post Newtonian approximation; at the point of dynamical collapse, we switch to a 1D (general relativistic) hydrodynamics code with the Misner-Sharpe metric. In opposition to a previous study, we do not find an explosion in the non rotating case, although our model is close to exploding for a similar mass to the explosion in the previous study. When we include slow rotation, we find one exploding model, and we conclude that there likely exist additional exploding models, though they may be rare.

In the blockchain-based, distributed computing platform Ethereum, programs called smart contracts are compiled to bytecode and executed on the Ethereum Virtual Machine (EVM). Executing EVM bytecode is subject to monetary fees---a clear optimization target. Our aim is to superoptimize EVM bytecode by encoding the operational semantics of EVM instructions as SMT formulas and leveraging a constraint solver to automatically find cheaper bytecode. We implement this approach in our EVM Bytecode SuperOptimizer ebso and perform two large scale evaluations on real-world data sets., Comment: 15 pages

We present two methods for proving confluence of left-linear term rewrite systems. One is hot-decreasingness, combining the parallel/development closedness theorems with rule labelling based on a terminating subsystem. The other is critical-pair-closing system, allowing to boil down the confluence problem to confluence of a special subsystem whose duplicating rules are relatively terminating., Comment: Added a reference to the conference version

We present ab-initio calculations of the electronic differential energy transfer (DET) cross-sections for antiprotons with energies between $3$keV and $1$MeV interacting with helium. By comparison with simulations employing the mean-field description based on the single-active electron approximation we are able to identify electron correlation effects in the stopping and straggling cross sections. Most remarkably, we find that straggling exceeds the celebrated Bohr straggling limit when correlated shake-up processes are included.

We study the dynamics of the massive Schwinger model on a lattice using exact diagonalization. When periodic boundary conditions are imposed, analytic arguments indicate that a non-zero electric flux in the initial state can "unwind" and decrease to a minimum value equal to minus its initial value, due to the effects of a pair of charges that repeatedly traverse the spatial circle. Our numerical results support the existence of this flux unwinding phenomenon, both for initial states containing a charged pair inserted by hand, and when the charges are produced by Schwinger pair production. We also study boundary conditions where charges are confined to an interval and flux unwinding cannot occur, and the massless limit, where our results agree with the predictions of the bosonized description of the Schwinger model., Comment: 8 pages, 7 figures

The entanglement swapping protocol is analyzed in a relativistic setting, where shortly after the entanglement swapping is performed, a Bell violation measurement is performed. From an observer in the laboratory frame, a Bell violation is observed due to entanglement swapping taking place, but in a moving frame the order of the measurements is reversed, and a Bell violation is observed even though no entanglement is present. Although the measurement results are identical, the wavefunctions for the two frames are different--- one is entangled and the other is not. Furthermore, for boosts in a perpendicular direction, in the presence of decoherence, we show that a maximum Bell violation can occur across non-simultaneous points in time. This is a signature of entanglement that is spread across both space and time, showing both the non-local and non-simultaneous feature of entanglement.

We study the extent to which the outcomes of a quantum measurement can be manipulated by changing the state of the measurement apparatus. The measurement process is modeled as decoherence induced by the experimenter, to gain knowledge about a particular system. The measurement apparatus is assumed to contain a large number of degrees of freedom, and the measurement outcomes are obtained by looking at the long interaction time limit. We study two cases which show contrasting behaviour. With a fixed axis coupling, the measurement is performed along the pointer basis with a high degree of robustness, for a wide variety of bath states. In a second model with Heisenberg interactions, the measurement outcomes can be altered considerably by changing the state of the bath.

Let a cluster be a term with a number of patterns occurring in it. We give two accounts of clusters, a geometric one as sets of (node and edge) positions, and an inductive one as pairs of terms with gaps (2nd order variables) and pattern-substitutions for the gaps. We show both notions of cluster and the corresponding refinement/coarsening orders on them, to be isomorphic. This equips clusters with a lattice structure which we lift to (parallel/multi) steps to yield an alternative account of the notion of critical peak., Comment: 6th International Workshop on Confluence

We present a useful web interface for tools that participate in the annual confluence competition., Comment: 6th International Workshop on Confluence

The rule labeling heuristic aims to establish confluence of (left-)linear term rewrite systems via decreasing diagrams. We present a formalization of a confluence criterion based on the interplay of relative termination and the rule labeling in the theorem prover Isabelle. Moreover, we report on the integration of this result into the certifier CeTA, facilitating the checking of confluence certificates based on decreasing diagrams. The power of the method is illustrated by an experimental evaluation on a (standard) collection of confluence problems.