@article{17534, abstract = {We propose a space-based interferometer surveying the gravitational wave (GW) sky in the milli-Hz to μ-Hz frequency range. By the 2040s, the μ-Hz frequency band, bracketed in between the Laser Interferometer Space Antenna (LISA) and pulsar timing arrays, will constitute the largest gap in the coverage of the astrophysically relevant GW spectrum. Yet many outstanding questions related to astrophysics and cosmology are best answered by GW observations in this band. We show that a μ-Hz GW detector will be a truly overarching observatory for the scientific community at large, greatly extending the potential of LISA. Conceived to detect massive black hole binaries from their early inspiral with high signal-to-noise ratio, and low-frequency stellar binaries in the Galaxy, this instrument will be a cornerstone for multimessenger astronomy from the solar neighbourhood to the high-redshift Universe.}, author = {Sesana, Alberto and Korsakova, Natalia and Sedda, Manuel Arca and Baibhav, Vishal and Barausse, Enrico and Barke, Simon and Berti, Emanuele and Bonetti, Matteo and Capelo, Pedro R. and Caprini, Chiara and Garcia-Bellido, Juan and Haiman, Zoltán and Jani, Karan and Jennrich, Oliver and Johansson, Peter H. and Khan, Fazeel Mahmood and Korol, Valeriya and Lamberts, Astrid and Lupi, Alessandro and Mangiagli, Alberto and Mayer, Lucio and Nardini, Germano and Pacucci, Fabio and Petiteau, Antoine and Raccanelli, Alvise and Rajendran, Surjeet and Regan, John and Shao, Lijing and Spallicci, Alessandro and Tamanini, Nicola and Volonteri, Marta and Warburton, Niels and Wong, Kaze and Zumalacarregui, Miguel}, issn = {0922-6435}, journal = {Experimental Astronomy}, number = {3}, pages = {1333--1383}, publisher = {Springer Science and Business Media LLC}, title = {{Unveiling the gravitational universe at μ-Hz frequencies}}, doi = {10.1007/s10686-021-09709-9}, volume = {51}, year = {2021}, } @article{17574, abstract = {As weak lensing surveys are becoming deeper and cover larger areas, information will be available on small angular scales down to the arcmin level. To extract this extra information, accurate modelling of baryonic effects is necessary. In this work, we adopt a baryonic correction model, which includes gas both bound inside and ejected from dark matter (DM) haloes, a central galaxy, and changes in the DM profile induced by baryons. We use this model to incorporate baryons into a large suite of DM-only N-body simulations, covering a grid of 75 cosmologies in the Ωm–σ8 parameter space. We investigate how baryons affect Gaussian and non-Gaussian weak lensing statistics and the cosmological parameter inferences from these statistics. Our results show that marginalizing over baryonic parameters degrades the constraints in Ωm–σ8 space by a factor of 2–5 compared to those with baryonic parameters fixed. We also find that combining the lensing power spectrum and peak counts can break the degeneracy between cosmological and baryonic parameters and mitigate the impact of the uncertainty in baryonic physics.}, author = {Lu, Tianhuan and Haiman, Zoltán}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {3}, pages = {3406--3417}, publisher = {Oxford University Press}, title = {{The impact of baryons on cosmological inference from weak lensing statistics}}, doi = {10.1093/mnras/stab1978}, volume = {506}, year = {2021}, } @article{17577, abstract = {The Legacy Survey of Space and Time (LSST) by the Vera C. Rubin Observatory is expected to discover tens of millions of quasars. A significant fraction of these could be powered by coalescing massive black hole (MBH) binaries, since many quasars are believed to be triggered by mergers. We show that under plausible assumptions about the luminosity functions, lifetimes, and binary fractions of quasars, we expect the full LSST quasar catalogue to contain between 20 and 100 million compact MBH binaries with masses M = 105–9M⊙, redshifts z = 0–6, and orbital periods P = 1–70 d. Their light-curves are expected to be distinctly periodic, which can be confidently distinguished from stochastic red-noise variability, because LSST will cover dozens, or even hundreds of cycles. A very small subset of 10–150 ultracompact (P ≲ 1 d) binary quasars among these will, over ∼5–15 yr, evolve into the mHz gravitational-wave frequency band and can be detected by LISA. They can therefore be regarded as ‘LISA verification binaries’, analogous to short-period Galactic compact-object binaries. The practical question is how to find these handful of ‘needles in the haystack’ among the large number of quasars: this will likely require a tailored co-adding analysis optimized for this purpose.}, author = {Xin, Chengcheng and Haiman, Zoltán}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {2}, pages = {2408--2417}, publisher = {Oxford University Press}, title = {{Ultra-short-period massive black hole binary candidates in LSST as LISA ‘verification binaries’}}, doi = {10.1093/mnras/stab1856}, volume = {506}, year = {2021}, } @article{17578, abstract = {If primordial black holes (PBHs) seeded the supermassive black holes (SMBHs) at the centers of high-redshift quasars, then the gas surrounding these black holes may reveal nucleosynthetic clues to their primordial origins. We present predictions of altered primordial abundances around PBHs massive enough to seed SMBHs at 𝑧≈6–7.5. We find that if PBHs with initial masses of ∼105  M⊙ are responsible for such SMBHs, they may produce primordial deuterium and Helium fractions enhanced by ≥10%, and lithium abundance depleted by ≥10%, at distances of up to ≈ a comoving kiloparsec away from the black hole after decoupling. We estimate that ∼108  M⊙ of gas is enhanced (or depleted) by at least one percent. Evidence of these modified primordial deuterium, helium, and lithium abundances could still be present if this circum-PBH gas remains unaccreted by the SMBH and in or near the host galaxies of high-redshift quasars. Measuring the abundance anomalies will be challenging, but could offer a novel way to reveal the primordial origin of such SMBH seeds.}, author = {Sanderbeck, Phoebe Upton and Bird, Simeon and Haiman, Zoltán}, issn = {2470-0010}, journal = {Physical Review D}, number = {10}, publisher = {American Physical Society}, title = {{Nucleosynthetic signatures of primordial origin around supermassive black holes}}, doi = {10.1103/physrevd.104.103022}, volume = {104}, year = {2021}, } @article{17583, abstract = {The astrophysical origin of gravitational wave transients is a timely open question in the wake of discoveries by the Laser Interferometer Gravitational-Wave Observatory (LIGO)/Virgo. In active galactic nuclei (AGNs), binaries form and evolve efficiently by interaction with a dense population of stars and the gaseous AGN disk. Previous studies have shown that stellar-mass black hole (BH) mergers in such environments can explain the merger rate and the number of suspected hierarchical mergers observed by LIGO/Virgo. The binary eccentricity distribution can provide further information to distinguish between astrophysical models. Here we derive the eccentricity distribution of BH mergers in AGN disks. We find that eccentricity is mainly due to binary–single (BS) interactions, which lead to most BH mergers in AGN disks having a significant eccentricity at 0.01 Hz, detectable by the Laser Interferometer Space Antenna. If BS interactions occur in isotropic-3D directions, then 8%–30% of the mergers in AGN disks will have eccentricities at 10 Hz above e10 Hz ≳ 0.03, detectable by LIGO/Virgo/Kamioka Gravitational Wave Detector, while 5%–17% of mergers have e10 Hz ≥ 0.3. On the other hand, if BS interactions are confined to the AGN–disk plane due to torques from the disk, with 1–20 intermediate binary states during each interaction, or if BHs can migrate to ≲ 10−3 pc from the central supermassive BH, then 10%–70% of the mergers will be highly eccentric (e10 Hz ≥ 0.3), consistent with the possible high eccentricity in GW190521.}, author = {Tagawa, Hiromichi and Kocsis, Bence and Haiman, Zoltán and Bartos, Imre and Omukai, Kazuyuki and Samsing, Johan}, issn = {2041-8205}, journal = {The Astrophysical Journal Letters}, number = {1}, publisher = {American Astronomical Society}, title = {{Eccentric black hole mergers in active galactic nuclei}}, doi = {10.3847/2041-8213/abd4d3}, volume = {907}, year = {2021}, } @article{17585, abstract = {Recent gravitational wave (GW) observations by LIGO/Virgo show evidence for hierarchical mergers, where the merging BHs are the remnants of previous BH merger events. These events may carry important clues about the astrophysical host environments of the GW sources. In this paper, we present the distributions of the effective spin parameter (χeff), the precession spin parameter (χp), and the chirp mass (mchirp) expected in hierarchical mergers. Under a wide range of assumptions, hierarchical mergers produce (i) a monotonic increase of the average of the typical total spin for merging binaries, which we characterize with χ¯typ≡(χ2eff+χ2p)1/2¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯, up to roughly the maximum mchirp among first-generation (1g) BHs, and (ii) a plateau at χ¯typ∼0.6 at higher mchirp. We suggest that the maximum mass and typical spin magnitudes for 1g BHs can be estimated from χ¯typ as a function of mchirp. The GW data observed in LIGO/Virgo O1--O3a prefers an increase in χ¯typ at low mchirp, which is consistent with the growth of the BH spin magnitude by hierarchical mergers, at ∼2σ confidence. A Bayesian analysis suggests that 1g BHs have the maximum mass of ∼15--30M⊙ if the majority of mergers are of high-generation BHs (not among 1g-1g BHs), which is consistent with mergers in active galactic nucleus disks and/or nuclear star clusters, while if mergers mainly originate from globular clusters, 1g BHs are favored to have non-zero spin magnitudes of ∼0.3. We also forecast that signatures for hierarchical mergers in the χ¯typ distribution can be confidently recovered once the number of GW events increases to ≳O(100).}, author = {Tagawa, Hiromichi and Haiman, Zoltán and Bartos, Imre and Kocsis, Bence and Omukai, Kazuyuki}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {3}, pages = {3362--3380}, publisher = {Oxford University Press}, title = {{Signatures of hierarchical mergers in black hole spin and mass distribution}}, doi = {10.1093/mnras/stab2315}, volume = {507}, year = {2021}, } @article{17586, abstract = {Variable active galactic nuclei showing periodic light curves have been proposed as massive black hole binary (MBHB) candidates. In such scenarios, the periodicity can be due to relativistic Doppler-boosting of the emitted light. This hypothesis can be tested through the timing of scattered polarized light. Following the results of polarization studies in type I nuclei and of dynamical studies of MBHBs with circumbinary discs, we assume a coplanar equatorial scattering ring, whose elements contribute differently to the total polarized flux, due to different scattering angles, levels of Doppler boost, and line-of-sight time delays. We find that in the presence of an MBHB, both the degree of polarization and the polarization position angle have periodic modulations. The polarization angle oscillates around the semiminor axis of the projected MBHB orbital ellipse, with a frequency equal either to the binary’s orbital frequency (for large scattering screen radii), or twice this value (for smaller scattering structures). These distinctive features can be used to probe the nature of periodic MBHB candidates and to compile catalogues of the most promising sub-pc MBHBs. The identification of such polarization features in gravitational-wave (GW) detected MBHBs would enormously increase the amount of physical information about the sources, allowing the measurement of the individual masses of the binary components, and the orientation of the line of nodes on the sky, even for monochromatic GW signals.}, author = {Dotti, Massimo and Bonetti, Matteo and D’Orazio, Daniel J and Haiman, Zoltán and Ho, Luis C}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {1}, pages = {212--223}, publisher = {Oxford University Press}, title = {{Binary black hole signatures in polarized light curves}}, doi = {10.1093/mnras/stab2893}, volume = {509}, year = {2021}, } @article{17589, abstract = {The origin of the black hole mergers detected by LIGO and Virgo remains an open question. While the unusual mass and spin of a few events constrain their possible astrophysical formation mechanisms, it is difficult to classify the bulk of the observed mergers. Here we consider the distribution of masses and spins in LIGO/Virgo's first and second observing catalogs, and find that for a significant fraction (25%) of these detected events, an AGN-disk origin model is preferred over a parametric mass-spin model fit to the full GWTC-2 merger sample (Bayes factor B>10). We use this to estimate the black hole merger rate in AGNs to be about 2.8±1.8\, Gpc−3yr−1, comparable to theoretical expectations. We find that AGNs can explain the rate and mass distribution of the observed events with primary black hole mass in the pair-instability mass gap (M≳50\, M⊙).}, author = {Gayathri, V. and Yang, Y. and Tagawa, H. and Haiman, Zoltán and Bartos, I.}, issn = {2041-8205}, journal = {The Astrophysical Journal Letters}, number = {2}, publisher = {American Astronomical Society}, title = {{Black hole mergers of AGN origin in LIGO–Virgo’s O1–O3a observing periods}}, doi = {10.3847/2041-8213/ac2cc1}, volume = {920}, year = {2021}, } @article{17592, abstract = {Using high-resolution hydrodynamics simulations, we show that equal-mass binaries accreting from a circumbinary disk evolve toward an orbital eccentricity of e ≃ 0.45, unless they are initialized on a nearly circular orbit with e ≲ 0.08, in which case they further circularize. The implied bi-modal eccentricity distribution resembles that seen in post-AGB stellar binaries. Large accretion spikes around periapse impart a tell-tale, quasiperiodic, bursty signature on the light curves of eccentric binaries. We predict that intermediate-mass and massive black hole binaries at z ≲ 10 entering the LISA band will have measurable eccentricities in the range of e ≃ 10−3 − 10−2, if they have experienced a gas-driven phase. On the other hand, GW190521 would have entered the LIGO/Virgo band with undetectable eccentricity ∼10−6 if it had been driven into the gravitational-wave regime by a gas disk.}, author = {Zrake, Jonathan and Tiede, Christopher and MacFadyen, Andrew and Haiman, Zoltán}, issn = {2041-8213}, journal = {The Astrophysical Journal Letters}, number = {1}, publisher = {American Astronomical Society}, title = {{Equilibrium eccentricity of accreting binaries}}, doi = {10.3847/2041-8213/abdd1c}, volume = {909}, year = {2021}, } @article{17593, abstract = {The science objectives of the LISA mission have been defined under the implicit assumption of a 4-years continuous data stream. Based on the performance of LISA Pathfinder, it is now expected that LISA will have a duty cycle of ≈0.75 , which would reduce the effective span of usable data to 3 years. This paper reports the results of a study by the LISA Science Group, which was charged with assessing the additional science return of increasing the mission lifetime. We explore various observational scenarios to assess the impact of mission duration on the main science objectives of the mission. We find that the science investigations most affected by mission duration concern the search for seed black holes at cosmic dawn, as well as the study of stellar-origin black holes and of their formation channels via multi-band and multi-messenger observations. We conclude that an extension to 6 years of mission operations is recommended.}, author = {Amaro Seoane, Pau and Arca Sedda, Manuel and Babak, Stanislav and Berry, Christopher P. L. and Berti, Emanuele and Bertone, Gianfranco and Blas, Diego and Bogdanović, Tamara and Bonetti, Matteo and Breivik, Katelyn and Brito, Richard and Caldwell, Robert and Capelo, Pedro R. and Caprini, Chiara and Cardoso, Vitor and Carson, Zack and Chen, Hsin-Yu and Chua, Alvin J. K. and Dvorkin, Irina and Haiman, Zoltán and Heisenberg, Lavinia and Isi, Maximiliano and Karnesis, Nikolaos and Kavanagh, Bradley J. and Littenberg, Tyson B. and Mangiagli, Alberto and Marcoccia, Paolo and Maselli, Andrea and Nardini, Germano and Pani, Paolo and Peloso, Marco and Pieroni, Mauro and Ricciardone, Angelo and Sesana, Alberto and Tamanini, Nicola and Toubiana, Alexandre and Valiante, Rosa and Vretinaris, Stamatis and Weir, David J. and Yagi, Kent and Zimmerman, Aaron}, issn = {0001-7701}, journal = {General Relativity and Gravitation}, number = {1}, publisher = {Springer Science and Business Media LLC}, title = {{The effect of mission duration on LISA science objectives}}, doi = {10.1007/s10714-021-02889-x}, volume = {54}, year = {2021}, } @article{17598, abstract = {The successive discoveries of binary merger events by Advanced LIGO-Virgo have been revealing the statistical properties of binary black hole (BBH) populations. A stochastic gravitational wave background (GWB) is a useful tool to probe the cosmological evolution of those compact mergers. In this paper, we study the upper bound on a GWB produced by BBH mergers, whose stellar progenitors dominate the reionization process at the cosmic dawn. Since early reionization by those progenitors yields a high optical depth of the universe inconsistent with the {\it Planck} measurements, the cumulative mass density is limited to ρ⋆≲107 M⊙ Mpc−3. Even with this upper bound, the amplitude of a GWB owing to the high-z BBH mergers is expected to be as high as Ωgw≃1.48+1.80−1.27×10−9 at f≃25 Hz, while their merger rate at the present-day is consistent or lower than the observed GW event rate. This level of GWB is detectable at the design sensitivity of Advanced LIGO-Virgo and would indicate a major contribution of the high-z BBH population to the local GW events. The spectral index is expected to be substantially flatter than the canonical value of ≃2/3 generically produced by lower-redshift and less massive BBHs. Moreover, if their mass function is more top-heavy than in the local universe, the GWB spectrum is even more skewed toward lower frequencies, which would allow us to extract information on the mass function of merging BBHs at high redshifts.}, author = {Inayoshi, Kohei and Kashiyama, Kazumi and Visbal, Eli and Haiman, Zoltán}, issn = {0004-637X}, journal = {The Astrophysical Journal}, number = {1}, publisher = {American Astronomical Society}, title = {{Gravitational wave backgrounds from coalescing black hole binaries at cosmic dawn: An upper bound}}, doi = {10.3847/1538-4357/ac106d}, volume = {919}, year = {2021}, } @article{17610, abstract = {The presence of massive black holes (BHs) with masses of order 109M⊙, powering bright quasars when the Universe was less than 1 Gyr old, poses strong constraints on their formation mechanism. Several scenarios have been proposed to date to explain massive BH formation, from the low-mass seed BH remnants of the first generation of stars to the massive seed BHs resulting from the rapid collapse of massive gas clouds. However, the plausibility of some of these scenarios to occur within the progenitors of high-z quasars has not yet been thoroughly explored. In this work, we investigate, by combining dark-matter only N-body simulations with a semi-analytic framework, whether the conditions for the formation of massive seed BHs from synchronised atomic-cooling halo pairs and/or dynamically-heated mini-haloes are fulfilled in the overdense regions where the progenitors of a typical high-redshift quasar host form and evolve. Our analysis shows that the peculiar conditions in such regions, i.e. strong halo clustering and high star formation rates, are crucial to produce a non-negligible number of massive seed BH host candidates: we find ≈1400 dynamically heated metal-free mini-haloes, including one of these which evolves to a synchronised pair and ends up in the massive quasar-host halo by z=6. This demonstrates that the progenitors of high-redshift quasar host haloes can harbour early massive seed BHs. Our results further suggest that multiple massive seed BHs may form in or near the quasar host's progenitors, potentially merging at lower redshifts and yielding gravitational wave events.}, author = {Lupi, Alessandro and Haiman, Zoltán and Volonteri, Marta}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {4}, pages = {5046--5060}, publisher = {Oxford University Press}, title = {{Forming massive seed black holes in high-redshift quasar host progenitors}}, doi = {10.1093/mnras/stab692}, volume = {503}, year = {2021}, } @article{17899, abstract = {Designing highly insulating sub-nanometer molecules is difficult because tunneling conductance increases exponentially with decreasing molecular length. This challenge is further enhanced by the fact that most molecules cannot achieve full conductance suppression with destructive quantum interference. Here, we present results for a series of small saturated heterocyclic alkanes where we show that conductance is suppressed due to destructive interference. Using the STM-BJ technique and density functional theory calculations, we confirm that their single-molecule junction conductance is lower than analogous alkanes of similar length. We rationalize the suppression of conductance in the junctions through analysis of the computed ballistic current density. We find there are highly symmetric ring currents, which reverse direction at the antiresonance in the Landauer transmission near the Fermi energy. This pattern has not been seen in earlier studies of larger bicyclic systems exhibiting interference effects and constitutes clear-cut evidence of destructive σ-interference. The finding of heterocyclic alkanes with destructive quantum interference charts a pathway for chemical design of short molecular insulators using organic molecules.}, author = {Zhang, Boyuan and Garner, Marc H. and Li, Liang and Campos, Luis M. and Solomon, Gemma C. and Venkataraman, Latha}, issn = {2041-6539}, journal = {Chemical Science}, number = {30}, pages = {10299--10305}, publisher = {Royal Society of Chemistry}, title = {{Destructive quantum interference in heterocyclic alkanes: The search for ultra-short molecular insulators}}, doi = {10.1039/d1sc02287c}, volume = {12}, year = {2021}, } @article{18192, abstract = {Current quantum simulation experiments are starting to explore nonequilibrium many-body dynamics in previously inaccessible regimes in terms of system sizes and timescales. Therefore, the question emerges as to which observables are best suited to study the dynamics in such quantum many-body systems. Using machine learning techniques, we investigate the dynamics and, in particular, the thermalization behavior of an interacting quantum system that undergoes a nonequilibrium phase transition from an ergodic to a many-body localized phase. We employ supervised and unsupervised training methods to distinguish nonequilibrium from equilibrium data, using the network performance as a probe for the thermalization behavior of the system. We test our methods with experimental snapshots of ultracold atoms taken with a quantum gas microscope. Our results provide a path to analyze highly entangled large-scale quantum states for system sizes where numerical calculations of conventional observables become challenging.}, author = {Bohrdt, A. and Kim, S. and Lukin, A. and Rispoli, M. and Schittko, R. and Knap, M. and Greiner, M. and Leonard, Julian}, issn = {0031-9007}, journal = {Physical Review Letters}, number = {15}, publisher = {American Physical Society}, title = {{Analyzing nonequilibrium quantum states through snapshots with artificial neural networks}}, doi = {10.1103/physrevlett.127.150504}, volume = {127}, year = {2021}, } @article{18193, abstract = {Topological states of matter, such as fractional quantum Hall states, are an active field of research due to their exotic excitations. In particular, ultracold atoms in optical lattices provide a highly controllable and adaptable platform to study such new types of quantum matter. However, finding a clear route to realize non-Abelian quantum Hall states in these systems remains challenging. Here we use the density-matrix renormalization-group (DMRG) method to study the Hofstadter-Bose-Hubbard model at filling factor 𝜈=1 and find strong indications that at 𝛼=1/6 magnetic flux quanta per plaquette the ground state is a lattice analog of the continuum non-Abelian Pfaffian. We study the on-site correlations of the ground state, which indicate its paired nature at 𝜈=1, and find an incompressible state characterized by a charge gap in the bulk. We argue that the emergence of a charge density wave on thin cylinders and the behavior of the two- and three-particle correlation functions at short distances provide evidence for the state being closely related to the continuum Pfaffian. The signatures discussed in this letter are accessible in current cold atom experiments and we show that the Pfaffian-like state is readily realizable in few-body systems using adiabatic preparation schemes.}, author = {Palm, F. A. and Buser, M. and Leonard, Julian and Aidelsburger, M. and Schollwöck, U. and Grusdt, F.}, issn = {2469-9969}, journal = {Physical Review B}, number = {16}, publisher = {American Physical Society}, title = {{Bosonic Pfaffian state in the Hofstadter-Bose-Hubbard model}}, doi = {10.1103/physrevb.103.l161101}, volume = {103}, year = {2021}, } @article{18233, abstract = {Neural network quantization enables the deployment of large models on resource-constrained devices. Current post-training quantization methods fall short in terms of accuracy for INT4 (or lower) but provide reasonable accuracy for INT8 (or above). In this work, we study the effect of quantization on the structure of the loss landscape. We show that the structure is flat and separable for mild quantization, enabling straightforward post-training quantization methods to achieve good results. We show that with more aggressive quantization, the loss landscape becomes highly non-separable with steep curvature, making the selection of quantization parameters more challenging. Armed with this understanding, we design a method that quantizes the layer parameters jointly, enabling significant accuracy improvement over current post-training quantization methods. Reference implementation is available at https://github.com/ynahshan/nn-quantization-pytorch/tree/master/lapq.}, author = {Nahshan, Yury and Chmiel, Brian and Baskin, Chaim and Zheltonozhskii, Evgenii and Banner, Ron and Bronstein, Alexander and Mendelson, Avi}, issn = {1573-0565}, journal = {Machine Learning}, number = {11-12}, pages = {3245--3262}, publisher = {Springer Nature}, title = {{Loss aware post-training quantization}}, doi = {10.1007/s10994-021-06053-z}, volume = {110}, year = {2021}, } @article{18235, abstract = {Recently, great progress has been made in the field of Few-Shot Learning (FSL). While many different methods have been proposed, one of the key factors leading to higher FSL performance is surprisingly simple. It is the backbone network architecture used to embed the images of the few-shot tasks. While first works on FSL resorted to small architectures with just a few convolution layers, recent works show that large architectures pre-trained on the training portion of FSL datasets produce strong features that are more easily transferable to novel few-shot tasks, thus attaining significant gains to methods using them. Despite these observations, little to no work has been done towards finding the right backbone for FSL. In this paper we propose MetAdapt that not only meta-searches for an optimized architecture for FSL using Network Architecture Search (NAS), but also results in a model that can adaptively ‘re-wire’ itself predicting the better architecture for a given novel few-shot task. Using the proposed approach we observe strong results on two popular few-shot benchmarks: miniImageNet and FC100.}, author = {Doveh, Sivan and Schwartz, Eli and Xue, Chao and Feris, Rogerio and Bronstein, Alexander and Giryes, Raja and Karlinsky, Leonid}, issn = {0167-8655}, journal = {Pattern Recognition Letters}, pages = {130--136}, publisher = {Elsevier}, title = {{MetAdapt: Meta-learned task-adaptive architecture for few-shot classification}}, doi = {10.1016/j.patrec.2021.05.010}, volume = {149}, year = {2021}, } @article{18237, abstract = {We present a novel method for neural network quantization. Our method, named UNIQ, emulates a non-uniform k-quantile quantizer and adapts the model to perform well with quantized weights by injecting noise to the weights at training time. As a by-product of injecting noise to weights, we find that activations can also be quantized to as low as 8-bit with only a minor accuracy degradation. Our non-uniform quantization approach provides a novel alternative to the existing uniform quantization techniques for neural networks. We further propose a novel complexity metric of number of bit operations performed (BOPs), and we show that this metric has a linear relation with logic utilization and power. We suggest evaluating the trade-off of accuracy vs. complexity (BOPs). The proposed method, when evaluated on ResNet18/34/50 and MobileNet on ImageNet, outperforms the prior state of the art both in the low-complexity regime and the high accuracy regime. We demonstrate the practical applicability of this approach, by implementing our non-uniformly quantized CNN on FPGA.}, author = {Baskin, Chaim and Liss, Natan and Schwartz, Eli and Zheltonozhskii, Evgenii and Giryes, Raja and Bronstein, Alexander and Mendelson, Avi}, issn = {1557-7333}, journal = {ACM Transactions on Computer Systems}, number = {1-4}, pages = {1--15}, publisher = {Association for Computing Machinery}, title = {{UNIQ: Uniform Noise Injection for Non-Uniform Quantization of neural networks}}, doi = {10.1145/3444943}, volume = {37}, year = {2021}, } @article{18238, abstract = {The demand for running NNs in embedded environments has increased significantly in recent years due to the significant success of convolutional neural network (CNN) approaches in various tasks, including image recognition and generation. The task of achieving high accuracy on resource-restricted devices, however, is still considered to be challenging, which is mainly due to the vast number of design parameters that need to be balanced. While the quantization of CNN parameters leads to a reduction of power and area, it can also generate unexpected changes in the balance between communication and computation. This change is hard to evaluate, and the lack of balance may lead to lower utilization of either memory bandwidth or computational resources, thereby reducing performance. This paper introduces a hardware performance analysis framework for identifying bottlenecks in the early stages of CNN hardware design. We demonstrate how the proposed method can help in evaluating different architecture alternatives of resource-restricted CNN accelerators (e.g., part of real-time embedded systems) early in design stages and, thus, prevent making design mistakes.}, author = {Karbachevsky, Alex and Baskin, Chaim and Zheltonozhskii, Evgenii and Yermolin, Yevgeny and Gabbay, Freddy and Bronstein, Alexander and Mendelson, Avi}, issn = {2071-1050}, journal = {Sustainability}, number = {2}, publisher = {MDPI}, title = {{Early-stage neural network hardware performance analysis}}, doi = {10.3390/su13020717}, volume = {13}, year = {2021}, } @inproceedings{18239, abstract = {Nowadays, there is an abundance of data involving images and surrounding free-form text weakly corresponding to those images. Weakly Supervised phrase-Grounding (WSG) deals with the task of using this data to learn to localize (or to ground) arbitrary text phrases in images without any additional annotations. However, most recent SotA methods for WSG assume an existence of a pre-trained object detector, relying on it to produce the ROIs for localization. In this work, we focus on the task of Detector-Free WSG (DF-WSG) to solve WSG without relying on a pre-trained detector. The key idea behind our proposed Grounding by Separation (GbS) method is synthesizing ‘text to image-regions’ associations by random alpha-blending of arbitrary image pairs and using the corresponding texts of the pair as conditions to recover the alpha map from the blended image via a segmentation network. At test time, this allows using the query phrase as a condition for a non-blended query image, thus interpreting the test image as a composition of a region corresponding to the phrase and the complement region. Our GbS shows an 8.5% accuracy improvement over previous DF-WSG SotA, for a range of benchmarks including Flickr30K, Visual Genome, and ReferIt, as well as a complementary improvement (above 7%) over the detector-based approaches for WSG.}, author = {Arbelle, Assaf and Doveh, Sivan and Alfassy, Amit and Shtok, Joseph and Lev, Guy and Schwartz, Eli and Kuehne, Hilde and Levi, Hila Barak and Sattigeri, Prasanna and Panda, Rameswar and Chen, Chun-Fu and Bronstein, Alexander and Saenko, Kate and Ullman, Shimon and Giryes, Raja and Feris, Rogerio and Karlinsky, Leonid}, booktitle = {IEEE/CVF International Conference on Computer Vision}, location = {Montreal, Canada}, publisher = {Institute of Electrical and Electronics Engineers}, title = {{Detector-free weakly supervised grounding by separation}}, doi = {10.1109/iccv48922.2021.00182}, volume = {15}, year = {2021}, }