We construct a Bayesian inference deep learning machine for parameter estimation of gravitational wave events of binaries of black hole coalescence. The structure of our deep Bayseian machine adopts the conditional variational autoencoder scheme by c
onditioning both the gravitational wave strains and the variations of amplitude spectral density of the detector noise. We show that our deep Bayesian machine is capable of yielding the posteriors compatible with the ones from the nest sampling method, and of fighting against the noise outliers. We also apply our deep Bayesian machine to the LIGO/Virgo O3 events, and find that conditioning detector noise to fight against its drifting is relevant for the events with medium signal-to-noise ratios.
It is known that a trained Restricted Boltzmann Machine (RBM) on the binary Monte Carlo Ising spin configurations, generates a series of iterative reconstructed spin configurations which spontaneously flow and stabilize to the critical point of physi
cal system. Here we construct a variety of Neural Network (NN) flows using the RBM and (variational) autoencoders, to study the q-state Potts and clock models on the square lattice for q = 2, 3, 4. The NN are trained on Monte Carlo spin configurations at various temperatures. We find that the trained NN flow does develop a stable point that coincides with critical point of the q-state spin models. The behavior of the NN flow is nontrivial and generative, since the training is unsupervised and without any prior knowledge about the critical point and the Hamiltonian of the underlying spin model. Moreover, we find that the convergence of the flow is independent of the types of NNs and spin models, hinting a universal behavior. Our results strengthen the potential applicability of the notion of the NN flow in studying various states of matter and offer additional evidence on the connection with the Renormalization Group flow.
We construct few deep generative models of gravitational waveforms based on the semi-supervising scheme of conditional autoencoders and their variational extensions. Once the training is done, we find that our best waveform model can generate the ins
piral-merger waveforms of binary black hole coalescence with more than $97%$ average overlap matched filtering accuracy for the mass ratio between $1$ and $10$. Besides, the generation time of a single waveform takes about one millisecond, which is about $10$ to $100$ times faster than the EOBNR algorithm running on the same computing facility. Moreover, these models can also help to explore the space of waveforms. That is, with mainly the low-mass-ratio training set, the resultant trained model is capable of generating large amount of accurate high-mass-ratio waveforms. This result implies that our generative model can speed up the waveform generation for the low latency search of gravitational wave events. With the improvement of the accuracy in future work, the generative waveform model may also help to speed up the parameter estimation and can assist the numerical relativity in generating the waveforms of higher mass ratio by progressively self-training.
Motivated by the recent discoveries of compact objects from LIGO/Virgo observations, we study the possibility of identifying some of these objects as compact stars made of dark matter called dark stars, or the mix of dark and nuclear matters called h
ybrid stars. In particular, in GW190814, a new compact object with 2.6 $M_{odot}$ is reported. This could be the lightest black hole, the heaviest neutron star, and a dark or hybrid star. In this work, we extend the discussion on the interpretations of the recent LIGO/Virgo events as hybrid stars made of various self-interacting dark matter (SIDM) in the isotropic limit. We pay particular attention to the saddle instability of the hybrid stars which will constrain the possible SIDM models.
We examine the weak cosmic censorship conjecture (WCCC) for the extremal charged black hole in possible generalizations of Einstein-Maxwell theory due to the higher order corrections, up to fourth-derivative terms. Our derivation is based on Walds ge
danken experiment to destroy an extremal black hole. We find that, provided the null energy condition for the falling matter, the WCCC is preserved for all possible generalizations. Thus, the WCCC cannot serve as a constraint to the higher order effective theories. We also show that up to first order variations of black hole mass and charge, WCCC is preserved for non-rotating extremal black holes in all $n$-dimensional diffeomorphism-covariant theories of gravity and $U(1)$ gauge field.
We study the Hawking flux from a black hole with soft hair by the anomaly cancellation method proposed by Robinson and Wilczek. Unlike the earlier studies considering the black hole with linear supertranslation hair, our study takes into account the
supertranslation hair to the quadratic order, which then yields the angular dependent horizon. As a result, highly nontrivial kinetic-mixings appear among the spherical Kaluza-Klein modes of the (1+1)d near-horizon reduced theory, which obscures the traditional derivation of the Hawking flux. However, after a series of field re-definitions, we can disentangle the mode-mixings into canonical normal modes, but the reduced metrics for these normal modes are mode-dependent. Despite of this, the resultant Hawking flux turns out to be mode-independent and remains the same as the Schwarzschilds one. Thus, one cannot tell the black holes with nonlinear supertranslation hairs from the Schwarzschilds one by examining the Hawking flux, so that the nonlinear soft hairs can be thought as the microstates.
We propose three scenarios for compact hybrid stars consisting of nuclear and dark matters which could possibly serve as alternative interpretations to the LIGO/Virgo events GW170817 and GW190425. To demonstrate our proposal, we adopt the SLy4 equati
on of state (EoS) for nuclear matter, and an EoS for a bosonic self-interacting dark matter (SIDM), which is simple and capable of yielding both reasonable halo density and compact stars. We study the mass-radius and tidal Love number (TLN)-mass relations for these compact hybrid stars, and also generalize the Bardeen-Thorne-Meltzer (BTM) criteria to discuss in details the possible saddle instability due to the nature of two-fluid model. Our results show that it is possible for our hybrid star scenarios to explain GW170817 and GW190425. Some of the hybrid stars can have compact neutron or mixed cores around 10km while possessing thick dark matter shells, which can then explain the astrophysical observations of neutron stars with compact photon radius and mass higher than 2 solar masses. Reversely, we also infer the dark matter model from the parameter estimation of GW190425. Our scenarios of compact hybrid stars can be further tested by the coming LIGO/Virgo O3 events.
Optomechanical interaction can be a platform for converting quantum optical sates at different frequencies. In this work, we propose to combine the idea of optomechanical frequency conversion and the dual-use of laser interferometer, for the purpose
of improving the broadband sensitivity of laser interferometer gravitational wave detectors by filtering the light field. We found that compare to the previous schemes of implementing the optomechanical devices in gravitational wave detectors, this frequency converter scheme will have less stringent requirement on the thermal noise dilution.
We consider gedanken experiments to destroy an extremal or near-extremal BTZ black hole by throwing matter into the horizon. These black holes are vacuum solutions to (2+1)-dimensional gravity theories, and are asymptotically $mathrm{AdS}_3$. Provide
d the null energy condition for the falling matter, we prove the following---(i) in a Mielke-Baekler model without ghost fields, when torsion is present, an extremal BTZ black hole can be overspun and becomes a naked conical singularity; (ii) in 3-dimensional Einstein gravity and chiral gravity, which both live in torsionless limits of Mielke-Baekler model, an extremal BTZ black hole cannot be overspun; and (iii) in both Einstein gravity and chiral gravity, a near-extremal BTZ black hole cannot be overspun, leaving the weak cosmic censorship preserved. To obtain these results, we follow the analysis of Sorce and Wald on their gedanken experiments to destroy a Kerr-Newman black hole, and calculate the second order corrections to the black hole mass. Furthermore, Walds type of gedanken experiment provides an operational procedure of proving the third law of black hole mechanics. Through the AdS/CFT correspondence, our results on BTZ black holes also indicate that a third law of thermodynamics holds for the holographic conformal field theories dual to 3-dimensional Einstein gravity and chiral gravity.
In the AdS$_3$/CFT$_2$ correspondence, we find some conformal field theory (CFT) states that have no bulk description by the Ba~nados geometry. We elaborate the constraints for a CFT state to be geometric, i.e., having a dual Ba~nados metric, by comp
aring the order of central charge of the entanglement/Renyi entropy obtained respectively from the holographic method and the replica trick in CFT. We find that the geometric CFT states fulfill Bohrs correspondence principle by reducing the quantum KdV hierarchy to its classical counterpart. We call the CFT states that satisfy the geometric constraints geometric states, and otherwise non-geometric states. We give examples of both the geometric and non-geometric states, with the latter case including the superposition states and descendant states.
