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We present our first set of results for charm physics, using the mixed-action setup introduced in a companion paper. Maximally twisted Wilson valence fermions are used on a sea of non-perturbatively $O(a)$-improved Wilson fermions, made up by CLS $N_{\mathrm{\scriptstyle f}}=2+1$ ensembles. Our charm-sector observables are free from $O(am_c)$ discretisation effects, without need of tuning any improvement coefficient, and show continuum-limit scaling properties consistent with leading cutoff effects of $O(a^2)$. We consider a subset of CLS ensembles -- including four values of the lattice spacing and pion masses down to 200 MeV -- allowing to take the continuum limit and extrapolate to the physical pion mass. A number of techniques are incorporated in the analysis in order to estimate the systematic uncertainties of our results for the charm quark mass and the $D_{(s)}$-meson decay constants. This first study of observables in the charm sector, where the emphasis has been on the control of the methodology, demonstrates the potential of our setup to achieve high-precision results., Comment: 44 pages, 21 figures

We report on our ongoing determination of the charm quark mass and the masses and decay constants of various charmed mesons, obtained within a mixed-action setup. We employ $N_f=2+1$ CLS ensembles combined with a Wilson twisted mass valence action that eliminates the leading $O(a)$ effects from our target observables. Alongside our preliminary results, we will discuss an exploration of GEVP techniques aimed at optimizing the precision in view of the extension of the computation to heavier quark masses. We study the chiral-continuum extrapolation of decay constants for charm quark observables and the renormalized charm quark mass., Comment: Proceedings of the 38th International Symposium on Lattice Field Theory, LATTICE2021 26th-30th July, 2021, Zoom/Gather@Massachusetts Institute of Technology

The first phase of a heavy quark program based on twisted mass valence quarks has been presented at last years's lattice conference. The CLS $N_f=2+1$ ensembles were used for their fine lattice spacing, while twisting the masses is expected to reduce discretisation errors even further and allow for a fully relativistic calculation. We present our strategy and preliminary results on three point functions, corresponding to $D\to K$ and $D\to\pi$ semileptonic decays. The form factors for $m_u=m_d=m_s$ quark masses obtained as a first step are shown here to be at the percent level in statistical precision at $q^2=0$., Comment: 7 pages, 3 figures, Presented at the 37th International Symposium on Lattice Field Theory (Lattice 2019), 16-22 June 2019, Wuhan, China

A mixed action composed of valence quark flavours regularized with a fully-twisted tmQCD action and of $N_f=2+1$ flavours of non-perturbatively ${\rm O}(a)$-improved Wilson sea quarks is described. Two procedures for the matching of sea and valence quark masses are discussed. We report about a comparison of the continuum-limit scaling of pseudoscalar meson observables and of quark masses using the sea and valence actions., Comment: Poster presented at the 36th Annual International Symposium on Lattice Field Theory, 22-28 July 2018, East Lansing, Michigan, USA. 7 pages, 8 figures, 1 table

We present preliminary results in the charm sector from a mixed-action setup, in which CLS $N_f=2+1$ ensembles are combined with a Wilson twisted mass valence action. We study the continuum and chiral limits of charm quark observables such as the decay constants $f_{D_{(s)}}$ and the renormalized charm-quark mass.

We introduce a mixed-action approach based on CLS ensembles, where a valence $N_f$=2+1+1 Twisted Mass QCD action is combined with the $N_f$=2+1 non-perturbatively O$(a)$-improved Wilson sea sector. We show that for maximally twisted valence quarks, the automatic O$(a)$-improvement of this set-up holds up to lattice artifacts coming from sea quark mass effects. Furthermore, we introduce a three-dimensional Gradient Flow smearing in order to tame the signal to noise ratio problem., Comment: 6 pages, 3 figures, talk presented at the 36th Annual International Symposium on Lattice Field Theory, 22-28 July 2018, East Lansing, Michigan, USA

We discuss an alternate scheme, or a 'line of constant physics', which can be used when computing isospin breaking corrections to hadronic quantities. We show that within a certain class of schemes one can separate the electromagnetic corrections from the strong isospin breaking corrections at leading order, meaning that within this class scheme-ambiguities are higher order effects., Comment: 6 pages, 1 figure, poster presented at the 36th Annual International Symposium on Lattice Field Theory, 22-28 July 2018, East Lansing, Michigan, USA

The great possibilities for strain engineering in core/shell nanowires have been explored as an alternative route to tailor the properties of binary III-V semiconductors without changing their chemical composition. In particular, we demonstrate that the GaAs core in GaAs/In(x)Ga(1-x)As or GaAs/In(x)Al(1-x)As core/shell nanowires can sustain unusually large misfit strains that would have been impossible in conventional thin-film heterostructures. The built-in strain in the core can be regulated via the composition and the thickness of the shell. Thick enough shells become almost strain-free, whereas the thin core undergoes a predominantly-hydrostatic tensile strain, which causes the reduction of the GaAs band gap energy. For the highest strain of 7 % in this work (obtained for x=0.54), a remarkable reduction of the band gap by 40 % was achieved in agreement with theoretical calculations. Such strong modulation of its electronic properties renders GaAs suitable for near-infrared nano-photonics and presumably high electron mobility nano-transistors., Comment: 12 pages, 4 figures

Within the HMC algorithm, we discuss how, by using the shadow Hamiltonian and the Poisson brackets, one can achieve a simple factorization in the dependence of the Hamiltonian violations upon either the algorithmic parameters or the parameters specifying the integrator. We consider the simplest case of a second order (nested) Omelyan integrator and one level of Hasenbusch splitting of the determinant for the simulations of a QCD-like theory (with gauge group SU(2)). Given the specific choice of the integrator, the Poisson brackets reduce to the variances of the molecular dynamics forces. We show how the factorization can be used to optimize in a very economical and simple way both the algorithmic and the integrator parameters with good accuracy., Comment: Version accepted for publication in Computer Physics Communications. Typos fixed. Formula 2.15 corrected. Discussion at the end of Section 3 rewritten. 19 pages, 8 figures

Recently researchers have proposed using deep learning-based systems for malware detection. Unfortunately, all deep learning classification systems are vulnerable to adversarial attacks. Previous work has studied adversarial attacks against static analysis-based malware classifiers which only classify the content of the unknown file without execution. However, since the majority of malware is either packed or encrypted, malware classification based on static analysis often fails to detect these types of files. To overcome this limitation, anti-malware companies typically perform dynamic analysis by emulating each file in the anti-malware engine or performing in-depth scanning in a virtual machine. These strategies allow the analysis of the malware after unpacking or decryption. In this work, we study different strategies of crafting adversarial samples for dynamic analysis. These strategies operate on sparse, binary inputs in contrast to continuous inputs such as pixels in images. We then study the effects of two, previously proposed defensive mechanisms against crafted adversarial samples including the distillation and ensemble defenses. We also propose and evaluate the weight decay defense. Experiments show that with these three defensive strategies, the number of successfully crafted adversarial samples is reduced compared to a standard baseline system without any defenses. In particular, the ensemble defense is the most resilient to adversarial attacks. Importantly, none of the defenses significantly reduce the classification accuracy for detecting malware. Finally, we demonstrate that while adding additional hidden layers to neural models does not significantly improve the malware classification accuracy, it does significantly increase the classifier's robustness to adversarial attacks.

We compute the leading QED corrections to the hadronic vacuum polarization (HVP) of the photon, relevant for the determination of leptonic anomalous magnetic moments, $a_\ell$. We work in the electroquenched approximation and use dynamical QCD configurations generated by the CLS initiative with two degenerate flavors of non-perturbatively O($a$)-improved Wilson fermions. We consider QED$_{\rm L}$ and QED$_{\rm M}$ to deal with the finite-volume zero modes. We compare results for the Wilson loops with exact analytical determinations. In addition we make sure that the volumes and photon masses used in QED$_{\rm M}$ are such that the correct dispersion relation is reproduced by the energy levels extracted from the charged pions two-point functions. Finally we compare results for pion masses and the HVP between QED$_{\rm L}$ and QED$_{\rm M}$. For the vacuum polarization, corrections with respect to the pure QCD case, at fixed pion masses, turn out to be at the percent level., Comment: 8 pages, 5 figures, 2 tabs, talk presented at the 35th International Symposium on Lattice Field Theory, 18-24 June 2017, Granada, Spain

We present some aspects of high precision calculations in the context of Lattice Quantum Field Theory. This work is a collection of three studies done during my Ph.D. period. First we present how to use the reweighting technique to compensate for the breaking of unitarity due to the use of different boundary conditions in the valence and sea sector. In particular when twisted boundary conditions are employed, with $\theta$ twisting angle. In large volume we found that the breaking is negligible, while in rather small volumes an effect is present. The quark mass appears to change with $\theta$ as a cutoff effect. In the second part of the dissertation we present an optimization method for Hybrid Monte Carlo performances. The work is based on the existence of a shadow Hamiltonian, an exactly conserved quantity along the Molecular Dynamics trajectory. The optimization method is economic since it only requires the forces to be measured, which are already used for the evolution from one configuration to the new one. We found predictions for the cost of the simulations with an accuracy of 10% and we could estimate the optimal parameters for the Omelyan integrator with mass-preconditioning and multi time-scale. In the last part of the work we address the calculation of electromagnetic corrections to the hadronic contribution to the $(g-2)$ anomaly of the muon. A long standing discrepancy between theoretical calculations and experimental results is present. But before invoking New Physics we need to clear the sight from possible effects within the Standard Model. In this exploratory study we carefully matched the masses of the charged pions in the theory with and without QED. We found a visible effect at the percent level although consistent with zero within two sigmas., Comment: Doctoral thesis. 161 pages, 33 figures, 8 tables. This thesis draws heavily from the works done during my Ph.D. period arXiv:1509.04540 , arXiv:1609.00210 and arXiv:1610.02860

We present a practical strategy to optimize a set of Hybrid Monte Carlo parameters in simulations of QCD and QCD-like theories. We specialize to the case of mass-preconditioning, with multiple time-step Omelyan integrators. Starting from properties of the shadow Hamiltonian we show how the optimal setup for the integrator can be chosen once the forces and their variances are measured, assuming that those only depend on the mass-preconditioning parameter., Comment: 7 pages, 5 figures, talk presented at the 34th International Symposium on Lattice Field Theory, 24-30 July 2016, Southampton, UK

We consider the possibility of using reweighting techniques in order to correct for the breaking of unitarity when twisted boundary conditions are imposed on valence fermions in simulations of lattice gauge theories. We start by studying the properties of reweighting factors and their variances at tree-level. That leads us to the introduction of a factorization for the fermionic reweighting determinant. In the numerical, stochastic, implementation of the method, we find that the effect of reweighting is negligible in the case of large volumes but it is sizeable when the volumes are small and the twisting angles are large. More importantly, we find that for un-improved Wilson fermions, and in small volumes, the dependence of the critical quark mass on the twisting angle is quite pronounced and results in large violations of the continuum dispersion relation., Comment: Version accepted for publication in Computer Physics Communications. Discussion extended in a few points. Results unchanged. 15 pages, 9 figures

We present precise lattice computations for the b-quark mass, the quark mass ratios mb/mc and mb/ms as well as the leptonic B-decay constants. We employ gauge configurations with four dynamical quark flavors, up/down, strange and charm, at three values of the lattice spacing (a ~ 0.06 - 0.09 fm) and for pion masses as low as 210 MeV. Interpolation in the heavy quark mass to the bottom quark point is performed using ratios of physical quantities computed at nearby quark masses exploiting the fact that these ratios are exactly known in the static quark mass limit. Our results are also extrapolated to the physical pion mass and to the continuum limit and read: mb(MSbar, mb) = 4.26(10) GeV, mb/mc = 4.42(8), mb/ms = 51.4(1.4), fBs = 229(5) MeV, fB = 193(6) MeV, fBs/fB = 1.184(25) and (fBs/fB)/(fK/fpi) = 0.997(17)., Comment: Version to appear in PRD. Added comments to simulation setup and error budget discussion. 1+20 pages, 9 figures

Imposing twisted boundary conditions on the fermionic fields is a procedure extensively used when evaluating, for example, form factors on the lattice. Twisting is usually performed for one flavour and only in the valence, and this causes a breaking of unitarity. In this work we explore the possibility of restoring unitarity through the reweighting method. We first study some properties of the approach at tree level and then we stochastically evaluate ratios of fermionic determinants for different boundary conditions in order to include them in the gauge averages, avoiding in this way the expensive generation of new configurations for each choice of the twisting angle, $\theta$. As expected the effect of reweighting is negligible in the case of large volumes but it is important when the volumes are small and the twisting angles are large. In particular we find a measurable effect for the plaquette and the pion correlation function in the case of $\theta=\pi/2$ in a volume $16\times 8^3$, and we observe a systematic upward shift in the pion dispersion relation., Comment: 7 pages, 9 figures, talk presented at the 33rd International Symposium on Lattice Field Theory, 14-18 July 2015, Kobe International Conference Center, Kobe, Japan

We discuss a lattice QCD computation of the $B$-meson decay constants by the ETM collaboration where suitable ratios allow to reach the bottom quark sector by combining simulations around the charm-quark mass with an exactly known static limit. The different steps involved in this ratio method are discussed together with an account of the assessment of various systematic effects. A comparison of results from simulations with two and four flavour dynamical quarks is presented., Comment: 8 pages, 4 figures. Proceedings of the 8th International Workshop on the CKM Unitarity Triangle (CKM 2014), Vienna, Austria, September 8-12, 2014

We present precision lattice calculations of the pseudoscalar decay constants of the charmed sector as well as determinations of the bottom quark mass and its ratio to the charm quark mass. We employ Nf=2+1+1 dynamical quark gauge configurations generated by the European Twisted Mass Collaboration, using data at three values of the lattice spacing and pion masses as low as 210 MeV. Strange and charm sea quark masses are close to their physical values., Comment: 7 pages, Contribution to the Proceedings of the 37th International Conference on High Energy Physics (ICHEP2014), Valencia, Spain, July 2-9, 2014