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Charged Higgs boson signatures via $pp \rightarrow H^\pm bj$ in 2HDM type-I

We show here that the suggested signatures can have sizable rates, reaching the pb level, when the top quark is produced on-shell and $\tan\beta$ is small. In this study, we investigate the light charged Higgs boson production via $pp \rightarrow H^\pm bj$ in the type-I configuration of the Two-Higgs Doublet Model (2HDM). In the viable parameter space, assuming either $h$ or $H$ is the SM-like Higgs boson observed at the Large Hadron Collider (LHC), we focus on the bosonic decays $H^\pm \rightarrow W^\pm A/h$ and examine the final states arising from the above charged Higgs production and decay. We show here that the suggested signatures can have sizable rates, reaching the pb level, when the top quark is produced on-shell and $\tan\beta$ is small.

Authors: R. Benbrik, M. Krab, B. Manaut, M. Ouchemhou.

Dynamical simulations of carotenoid photoexcited states using density matrix renormalization group techniques

Chem. A}$ (2023).

We present a dynamical simulation scheme to model the highly correlated excited state dynamics of linear polyenes. We apply it to investigate the internal conversion processes of carotenoids following their photoexcitation. We use the extended Hubbard-Peierls model, $\hat{H}_{\textrm{UVP}}$, to describe the $\pi$-electronic system coupled to nuclear degrees of freedom supplemented by a Hamiltonian, $\hat{H}_{\epsilon}$, that explicitly breaks both the particle-hole and two-fold rotation symmetries of idealized carotenoids. The electronic degrees of freedom are treated quantum mechanically by solving the time-dependent Schr\"odinger equation using the adaptive time-dependent DMRG (tDMRG) method, while nuclear dynamics are treated via the Ehrenfest equations of motion. By defining adiabatic excited states as the eigenstates of the full Hamiltonian, $\hat{H}=\hat{H}_{\textrm{UVP}}+\hat{H}_{\epsilon}$, and diabatic excited states as eigenstates of $\hat{H}_{\textrm{UVP}}$, we present a computational framework to monitor the internal conversion process from the initial photoexcited state to the singlet triplet-pair states of carotenoids. We further incorporate Lanczos-DMRG to the tDMRG-Ehrenfest method to calculate transient absorption spectra from the evolving photoexcited state. We describe the accuracy and convergence criteria for DMRG, and show that this method accurately describes the dynamics of carotenoid excited states. We also discuss the effect of $\hat{H}_{\epsilon}$ on the internal conversion process, and show that its effect on the extent of internal conversion can be described by a Landau-Zener-type transition. This methodological paper is a companion to our more explanatory discussion of carotenoid excited state dynamics in, $\textit{Photoexcited state dynamics and singlet fission in carotenoids}$, D. Manawadu, T. N. Georges and W. Barford, $\textit{J. Phys. Chem. A}$ (2023).

Authors: Dilhan Manawadu, Darren J. Valentine, William Barford.

Foot-Sorting for Socks

If your socks come out of the laundry all mixed up, how should you sort them? We give an enumeration involving Fibonacci numbers for the $1$-foot-sortable sock orderings within a naturally-arising class. If your socks come out of the laundry all mixed up, how should you sort them? We introduce and study a novel foot-sorting algorithm that uses feet to attempt to sort a sock ordering; one can view this algorithm as an analogue of Knuth's stack-sorting algorithm for set partitions. The sock orderings that can be sorted using a fixed number of feet are characterized by Klazar's notion of set partition pattern containment. We give an enumeration involving Fibonacci numbers for the $1$-foot-sortable sock orderings within a naturally-arising class. We also prove that if you have socks of $n$ different colors, then you can always sort them using at most $\left\lceil\log_2(n)\right\rceil$ feet, and we use a Ramsey-theoretic argument to show that this bound is tight.

Authors: Colin Defant, Noah Kravitz.

Sensitivity of Bayesian Casual Forests to Modeling Choices: A Re-analysis of the 2022 ACIC Data Challenge

We demonstrate how Hahn et al.

We demonstrate how Hahn et al.'s Bayesian Causal Forests model (BCF) can be used to estimate conditional average treatment effects for the longitudinal dataset in the 2022 American Causal Inference Conference Data Challenge. Unfortunately, existing implementations of BCF do not scale to the size of the challenge data. Therefore, we developed flexBCF -- a more scalable and flexible implementation of BCF -- and used it in our challenge submission. We investigate the sensitivity of our results to two ad hoc modeling choices we made during our initial submission: (i) the choice of propensity score estimation method and (ii) the use of sparsity-inducing regression tree priors. While we found that our overall point predictions were not especially sensitive to these modeling choices, we did observe that running BCF with flexibly estimated propensity scores often yielded better-calibrated uncertainty intervals.

Authors: Ajinkya H. Kokandakar, Hyunseung Kang, Sameer K. Deshpande.

Extending the analogy between intracellular motion in mammalian cells and glassy dynamics

In mammalian cells, in particular, cellular vesicles move across the cell using motor proteins that carry the vesicle down the cytoskeleton to their destination. Analysing this motion quantitatively, we observe a displacement distribution that is roughly Gaussian for shorter distances ($\lesssim$ 0.05 $\mu$m) but which exhibits exponentially decaying tails at longer distances (up to 0.40 $\mu$m). We show that this behaviour is well-described by a model originally developed to describe the motion in glassy systems. Overall, we demonstrate the ubiquity of glass-like motion in mammalian cells, providing a different perspective on intracellular motion. The physics of how molecules, organelles, and foreign objects move within living cells has been extensively studied in organisms ranging from bacteria to human cells. In mammalian cells, in particular, cellular vesicles move across the cell using motor proteins that carry the vesicle down the cytoskeleton to their destination. We have recently noted several similarities between the motion of such vesicles and that in disordered, "glassy", systems, but it remains unclear whether that is a general observation or something specific to certain vesicles in one particular cell type. Here we follow the motion of mitochondria, the organelles responsible for cell energy production, in several mammalian cell types over timescales ranging from 50 ms up to 70 s. Qualitative observations show that single mitochondria remain stalled, remaining within a spatially limited region, for extended periods of time, before moving longer distances relatively quickly. Analysing this motion quantitatively, we observe a displacement distribution that is roughly Gaussian for shorter distances ($\lesssim$ 0.05 $\mu$m) but which exhibits exponentially decaying tails at longer distances (up to 0.40 $\mu$m). We show that this behaviour is well-described by a model originally developed to describe the motion in glassy systems. These observations are extended to in total 3 different objects (mitochondria, lysosomes and nano-sized beads enclosed in vesicles), 3 different mammalian cell types, from 2 different organisms (human and mouse). We provide further evidence that supports glass-like characteristics of the motion by showing a difference between the time it takes to move a longer distance for the first time and subsequent times, as well as a weak ergodicity breaking of the motion. Overall, we demonstrate the ubiquity of glass-like motion in mammalian cells, providing a different perspective on intracellular motion.

Authors: B. Corci, O. Hooiveld, A. M. Dolga, C. Åberg.

A unconditionally energy dissipative, adaptive IMEX BDF2 scheme and its error estimates for Cahn-Hilliard equation on generalized SAV approach

It is proved that the modified energy dissipation law is unconditionally preserved at discrete levels. The proof involves the tools of discrete orthogonal convolution (DOC) kernels and inequality zoom. Finally, numerical examples are provided to verify our theoretical analysis and the algorithm efficiency.

An adaptive implicit-explicit (IMEX) BDF2 scheme is investigated on generalized SAV approach for the Cahn-Hilliard equation by combining with Fourier spectral method in space. It is proved that the modified energy dissipation law is unconditionally preserved at discrete levels. Under a mild ratio restriction, i.e., \Ass{1}: $0<r_k:=\tau_k/\tau_{k-1}< r_{\max}\approx 4.8645$, we establish a rigorous error estimate in $H^1$-norm and achieve optimal second-order accuracy in time. The proof involves the tools of discrete orthogonal convolution (DOC) kernels and inequality zoom. It is worth noting that the presented adaptive time-step scheme only requires solving one linear system with constant coefficients at each time step. In our analysis, the first-consistent BDF1 for the first step does not bring the order reduction in $H^1$-norm. The $H^1$ bound of the numerical solution under periodic boundary conditions can be derived without any restriction (such as zero mean of the initial data). Finally, numerical examples are provided to verify our theoretical analysis and the algorithm efficiency.

Authors: Yifan Wei, Jiwei Zhang, Chengchao Zhao, Yanmin Zhao.

A cryogenic SRAM based arbitrary waveform generator in 14 nm for spin qubit control

We propose an SRAM based arbitrary waveform generator for cryogenic control of spin qubits. The waveform sequence from a control processor can be stored in an SRAM memory array, which can be programmed in real time. The waveform pattern is converted to microwave pulses by a source-series-terminated digital to analog converter. Total power consumption of the AWG is 40-140mW at 4 K, depending upon the baud rate. Realization of qubit gate sequences require coherent microwave control pulses with programmable amplitude, duration, spacing and phase. We propose an SRAM based arbitrary waveform generator for cryogenic control of spin qubits. We demonstrate in this work, the cryogenic operation of a fully programmable radio frequency arbitrary waveform generator in 14 nm FinFET technology. The waveform sequence from a control processor can be stored in an SRAM memory array, which can be programmed in real time. The waveform pattern is converted to microwave pulses by a source-series-terminated digital to analog converter. The chip is operational at 4 K, capable of generating an arbitrary envelope shape at the desired carrier frequency. Total power consumption of the AWG is 40-140mW at 4 K, depending upon the baud rate. A wide signal band of 1-17 GHz is measured at 4 K, while multiple qubit control can be achieved using frequency division multiplexing at an average spurious free dynamic range of 40 dB. This work paves the way to optimal qubit control and closed loop feedback control, which is necessary to achieve low latency error mitigation

Authors: Mridula Prathapan, Peter Mueller, Christian Menolfi, Matthias Braendli, Marcel Kossel, Pier Andrea Francese, David Heim, Maria Vittoria Oropallo, Andrea Ruffino, Cezar Zota, Thomas Morf.

Oracle Inequalities for Model Selection in Offline Reinforcement Learning

A major challenge in applying such methods in practice is the lack of both theoretically principled and practical tools for model selection and evaluation. We conclude with several numerical simulations showing it is capable of reliably selecting a good model class.

In offline reinforcement learning (RL), a learner leverages prior logged data to learn a good policy without interacting with the environment. A major challenge in applying such methods in practice is the lack of both theoretically principled and practical tools for model selection and evaluation. To address this, we study the problem of model selection in offline RL with value function approximation. The learner is given a nested sequence of model classes to minimize squared Bellman error and must select among these to achieve a balance between approximation and estimation error of the classes. We propose the first model selection algorithm for offline RL that achieves minimax rate-optimal oracle inequalities up to logarithmic factors. The algorithm, ModBE, takes as input a collection of candidate model classes and a generic base offline RL algorithm. By successively eliminating model classes using a novel one-sided generalization test, ModBE returns a policy with regret scaling with the complexity of the minimally complete model class. In addition to its theoretical guarantees, it is conceptually simple and computationally efficient, amounting to solving a series of square loss regression problems and then comparing relative square loss between classes. We conclude with several numerical simulations showing it is capable of reliably selecting a good model class.

Authors: Jonathan N. Lee, George Tucker, Ofir Nachum, Bo Dai, Emma Brunskill.

On the Turán number of the hypercube

This answers a question of Liu. Moreover, our techniques give a power improvement for a larger class of graphs than cubes. This latter result is tight. In 1964, Erd\H{o}s proposed the problem of estimating the Tur\'an number of the $d$-dimensional hypercube $Q_d$. Since $Q_d$ is a bipartite graph with maximum degree $d$, it follows from results of F\"uredi and Alon, Krivelevich, Sudakov that $\mathrm{ex}(n,Q_d)=O_d(n^{2-1/d})$. A recent general result of Sudakov and Tomon implies the slightly stronger bound $\mathrm{ex}(n,Q_d)=o(n^{2-1/d})$. We obtain the first power-improvement for this old problem by showing that $\mathrm{ex}(n,Q_d)=O_d(n^{2-\frac{1}{d-1}+\frac{1}{(d-1)2^{d-1}}})$. This answers a question of Liu. Moreover, our techniques give a power improvement for a larger class of graphs than cubes. We use a similar method to prove that any $n$-vertex, properly edge-coloured graph without a rainbow cycle has at most $O(n(\log n)^2)$ edges, improving the previous best bound of $n(\log n)^{2+o(1)}$ by Tomon. Furthermore, we show that any properly edge-coloured $n$-vertex graph with $\omega(n\log n)$ edges contains a cycle which is almost rainbow: that is, almost all edges in it have a unique colour. This latter result is tight.

Authors: Oliver Janzer, Benny Sudakov.

On the classicality of quantum dephasing processes

We find a rich phenomenology of quantum dephasing processes which can be interpreted in classical terms. For non-Markovian processes, classicality can only be proven in the fully compatible case, thus revealing a key difference between Markovian and non-Markovian pure dephasing processes.

We analyze the multitime statistics associated with pure dephasing systems repeatedly probed with sharp measurements, and search for measurement protocols whose statistics satisfies the Kolmogorov consistency conditions possibly up to a finite order. We find a rich phenomenology of quantum dephasing processes which can be interpreted in classical terms. In particular, if the underlying dephasing process is Markovian, we find sufficient conditions under which classicality at every order can be found: this can be reached by choosing the dephasing and measurement basis to be fully compatible or fully incompatible, that is, mutually unbiased bases (MUBs). For non-Markovian processes, classicality can only be proven in the fully compatible case, thus revealing a key difference between Markovian and non-Markovian pure dephasing processes.

Authors: Davide Lonigro, Dariusz Chruściński.