Thu·Apr 26, 2018Thursday·April 26, 2018

1. 01*

   Opening the black box of neural nets: case studies in stop/top discrimination

   Thomas Roxlo🇺🇸 · Matthew Reece🇺🇸

   We introduce techniques for exploring the functionality of a neural network and extracting simple, human-readable approximations to its performance. By performing gradient ascent on the input space of the network, we are able to produce large populations of artificial events which strongly excite a given classifier. By studying the populations of these events, we then directly produce what are essentially contour maps of the network's classification function. Combined with a suite of tools for identifying the input dimensions deemed most important by the network, we can utilize these maps to efficiently interpret the dominant criteria by which the network makes its classification. As a test case, we study networks trained to discriminate supersymmetric stop production in the dilepton channel from Standard Model backgrounds. In the case of a heavy stop decaying to a light neutralino, we find individual neurons with large mutual information with $m_{T2}^{\ell \ell }$, a human-designed variable for optimizing the analysis. The network selects events with significant missing $p_T$ oriented azimuthally away from both leptons, efficiently rejecting $t\overline{t}$ background. In the case of a light stop with three-body decays to $Wb\tilde{\chi }$ and little phase space, we find neurons that smoothly interpolate between a similar top-rejection strategy and an ISR-tagging strategy allowing for more missing momentum. We also find that a neural network trained on a stealth stop parameter point learns novel angular correlations.

   hep-phstat.ML29 citations
2. 02*

   Diffractive Vector Photoproduction using Holographic QCD

   Chang Hwan Lee🇰🇷 · Hui-Young Ryu🇰🇷 · Ismail Zahed🇺🇸

   We discuss diffractive photon-production of vector mesons in holographic QCD. At large $\sqrt{s}$, the QCD scattering amplitudes are reduced to the scattering of pair of dipoles exchanging a closed string or a pomeron. We use the holographic construction in AdS${}_5$ to describe both the intrinsic dipole distribution in each hadron, and the pomeron exchange. Our results for the heavy meson photon-production are made explicit and compared to some existing experiments.

   hep-phPRD(2018)·11 citations
3. 03*

   Hidden-strange molecular states and the $N\varphi$ bound state via a QCD van der Waals force

   Jun He🇨🇳 · Hongxia Huang🇨🇳 · Dian-Yong Chen🇨🇳 · Xinmei Zhu🇨🇳

   In this work, we study the hidden-strange molecular states composed of a baryon and a vector meson in a coupled-channel $N\rho -N\omega -N\varphi -\Lambda K^{\ast }-\Sigma K^{\ast }$ interaction. With the help of the effective Lagrangians which coupling constants are determined by the SU(3) symmetry, the interaction is constructed and inserted into the quasipotential Bethe-Salpeter equation to search for poles in the complex plane, which correspond to molecular states. Two poles are found with a spin parity $3/2^{-}$ near the $N\rho$ and the $\Sigma K^{\ast }$ thresholds, which can be related to the $N(1700)$ and the $N(2100)$, respectively. No pole near the $N\varphi$ threshold can be found if direct interaction between a nucleon and $\varphi$ meson is neglected according to the OZI rule. After introducing the QCD van der Waals force between a nucleon and $\varphi$ meson, a narrow state can be produced near the $N\varphi$ threshold. Inclusion of the QCD van der Waals force changes the line shape of the invariant mass spectrum in the $N\varphi$ channel leading to a worse agreement with the present low-precision data. Future experiments at BelleII, JLab, and other facilities will be very helpful to clarify the existence of these possible hidden-strange molecular states.

   hep-phnucl-exnucl-thPRD(2018)·15 citations
4. 04*

   Uncertainties in the Lightest $CP$ Even Higgs Boson Mass Prediction in the Minimal Supersymmetric Standard Model: Fixed Order Versus Effective Field Theory Prediction

   B.C. Allanach🇬🇧 · A. Voigt🇩🇪

   We quantify and examine the uncertainties in predictions of the lightest $CP$ even Higgs boson pole mass $M_h$ in the Minimal Supersymmetric Standard Model (MSSM), utilising current spectrum generators and including some three-loop corrections. There are two broadly different approximations being used: effective field theory (EFT) where an effective Standard Model (SM) is used below a supersymmetric mass scale, and a fixed order calculation, where the MSSM is matched to QCD$\times$QED at the electroweak scale. The uncertainties on the $M_h$ prediction in each approach are broken down into logarithmic and finite pieces. The inferred values of the stop mass parameters are sensitively dependent upon the precision of the prediction for $M_h$. The fixed order calculation appears to be more accurate below a supersymmetry (SUSY) mass scale of $M_S\approx 1.2$ TeV, whereas above this scale, the EFT calculation is more accurate. We also revisit the range of the lightest stop mass across fine-tuned parameter space that has an appropriate stable vacuum and is compatible with the lightest $CP$ even Higgs boson $h$ being identified with the one discovered at the ATLAS and CMS experiments in 2012; we achieve a maximum value of $\sim 10^{11}$ GeV.

   hep-phEPJC(2018)·38 citations
5. 05*

   Prospects for Sneutrino Dark Matter in the BLSSM

   Luigi Delle Rose🇬🇧 · Shaaban Khalil🇪🇬 · Simon J.D. King🇬🇧 · Suchita Kulkarni🇦🇹 · Carlo Marzo🇪🇪 · Stefano Moretti🇬🇧 · Cem S. Un🇹🇷

   The $(B-L)$ Supersymmetric Standard Model (BLSSM) motivates several Dark Matter (DM) candidates beyond the Minimally Supersymmetric Standard Model (MSSM). We assess the comparative naturalness of the two models and discuss the potential detection properties of a particular candidate, the Right-Handed (RH) sneutrino.

   hep-phNuovo Cim.C(2019)·2 citations
6. 06*

   Analyzing "magnetic moments in curved spacetime": pitfalls in GR

   David Venhoek🇳🇱

   We analyze the classical approximations made in "The general relativistic effects to the magnetic moment in the Earth's gravity", originally published as "Post-Newtonian effects of Dirac particle in curved spacetime - I : magnetic moment in curved spacetime", and work out precisely where in the argument the mistakes are made. We show explicitly that any difference vanishes when properly distinguishing between coordinate and physical distance. In doing this, we illustrate some of the pitfalls in using GR to make predictions.

   hep-phgr-qc6 citations
7. 07*

   Drag force on heavy diquarks and gauge/string duality

   Oleg Andreev🇷🇺

   We use gauge/string duality to model a doubly heavy diquark in a color antitriplet moving in a thermal plasma at temperatures near the critical. With the assumption that there is no relative motion between the constituents, we calculate the drag force on the diquark. At high enough speed we find that diquark string configurations develop a cusp. In addition, we estimate the spatial string tension at non-zero baryon chemical potential, and also briefly discuss an extension to a triply heavy triquark in a color triplet.

   hep-phhep-lathep-thnucl-thPRD(2018)·6 citations
8. 08*

   Scale independence in an asymptotically free theory at finite temperatures

   Gabriel N. Ferrari🇧🇷

   A recently developed variational resummation technique incorporating renormalization group properties has been shown to solve the scale dependence problem that plagues the evaluation of thermodynamical quantities, e.g., within the framework of approximations such as in the hard-thermal-loop resummed perturbation theory. This method is used in the present work to evaluate thermodynamical quantities within the two-dimensional nonlinear sigma model, which shares some common features with Yang-Mills theories, like asymptotic freedom, trace anomaly and the nonperturbative generation of a mass gap. Besides the fact that nonperturbative results can be readily generated solely by considering the lowest-order contribution to the thermodynamic effective potential, we also show that its next-to-leading correction indicates convergence to the sought-after scale invariance.

   hep-ph0 citations
9. 09*

   Quark-antiquark potentials in non-perturbative models

   C. Mena🇧🇷 · L. F. Palhares🇧🇷

   In these proceedings, we investigate non-perturbative models for Quantum Chromodynamics (QCD) motivated by the behavior of the Landau-gauge lattice gluon propagator with the purpose of testing their validity in the perturbative regime of strong interactions and to explore their behavior in the infrared region. In particular, we discuss the potentials between heavy quarks and antiquarks, since this observable might reveal the appearance of confining properties in these non-perturbative models through a linear growth at large and intermediate distances.

   hep-ph5 citations
10. 10*

    Active-sterile neutrino oscillations at INO-ICAL over a wide mass-squared range

    Tarak Thakore🇺🇸 · Moon Moon Devi🇪🇸 · Sanjib Kumar Agarwalla🇮🇳 · Amol Dighe🇮🇳

    We perform a detailed analysis for the prospects of detecting active-sterile oscillations involving a light sterile neutrino, over a large $\Delta m_{41}^2$ range of $10^{-5}$ eV${}^2$ to $10^2$ eV${}^2$, using 10 years of atmospheric neutrino data expected from the proposed 50 kt magnetized ICAL detector at the INO. This detector can observe the atmospheric ${\nu }_{\mu }$ and ${\bar{\nu }}_{\mu }$ separately over a wide range of energies and baselines, making it sensitive to the magnitude and sign of $\Delta m_{41}^2$ over a large range. If there is no light sterile neutrino, ICAL can place competitive upper limit on $|U_{\mu 4}{|}^2\lesssim 0.02$ at 90\% C.L. for $\Delta m_{41}^2$ in the range $(0.5-5)\times 10^{-3}$ eV${}^2$. For the same $|\Delta m_{41}^2|$ range, ICAL would be able to determine its sign, exploiting the Earth's matter effect in ${\mu }^{-}$ and ${\mu }^{+}$ events separately if there is indeed a light sterile neutrino in Nature. This would help identify the neutrino mass ordering in the four-neutrino mixing scenario.

    hep-phhep-exphysics.ins-detJHEP(2018)·25 citations
11. 11*

    Low-Scale Leptogenesis in the Scotogenic Neutrino Mass Model

    Thomas Hugle🇩🇪 · Moritz Platscher🇩🇪 · Kai Schmitz🇩🇪

    The scotogenic model proposed by Ernest Ma represents an attractive and minimal example for the generation of small Standard Model neutrino masses via radiative corrections in the dark matter sector. In this paper, we demonstrate that, in addition to neutrino masses and dark matter, the scotogenic model also allows to explain the baryon asymmetry of the Universe via low-scale leptogenesis. First, we consider the case of two right-handed neutrinos (RHNs) N_{1,2}, for which we provide an analytical argument why it is impossible to push the RHN mass scale below M_1^min ~ 10^10 GeV, which is identical to the value in standard thermal leptogenesis in the type-I seesaw scenario with the same washout strength. Then, we present a detailed study of the three-RHN case based on both an analytical and a numerical analysis. In the case of three RHNs, we obtain a lower bound on the N_1 mass of around 10 TeV. Remarkably enough, successful low-scale leptogenesis can be achieved without any degeneracy in the RHN mass spectrum. The only necessary condition is a suppression in the N_1 Yukawa couplings, which results in suppressed washout and a small active neutrino mass of around 10^-12 eV. This leads to the fascinating realization that low-scale leptogenesis in the scotogenic model can be tested in experiments that aim at measuring the absolute neutrino mass scale.

    hep-phastro-ph.COhep-exPRD(2018)·114 citations
12. 12*

    Current unknowns in the three neutrino framework

    F. Capozzi🇩🇪 · E. Lisi🇮🇹 · A. Marrone🇮🇹 · A. Palazzo🇮🇹

    We present an up-to-date global analysis of data coming from neutrino oscillation and non-oscillation experiments, as available in April 2018, within the standard framework including three massive and mixed neutrinos. We discuss in detail the status of the three-neutrino (3nu) mass-mixing parameters, both known and unknown. Concerning the latter, we find that: normal ordering (NO) is favored over inverted ordering (IO) at 3sigma level; the Dirac CP phase is constrained within ~15% (~9%) uncertainty in NO (IO) around nearly-maximal CP-violating values; the octant of the largest mixing angle and the absolute neutrino masses remain undetermined. We briefly comment on other unknowns related to theoretical and experimental uncertainties (within 3nu) or possible new states and interactions (beyond 3nu).

    hep-phastro-ph.COhep-exnucl-exPPNP(2018)·296 citations
13. 13*

    JUNIPR: a Framework for Unsupervised Machine Learning in Particle Physics

    Anders Andreassen🇺🇸 · Ilya Feige🇬🇧 · Christopher Frye🇺🇸 · Matthew D. Schwartz🇺🇸

    In applications of machine learning to particle physics, a persistent challenge is how to go beyond discrimination to learn about the underlying physics. To this end, a powerful tool would be a framework for unsupervised learning, where the machine learns the intricate high-dimensional contours of the data upon which it is trained, without reference to pre-established labels. In order to approach such a complex task, an unsupervised network must be structured intelligently, based on a qualitative understanding of the data. In this paper, we scaffold the neural network's architecture around a leading-order model of the physics underlying the data. In addition to making unsupervised learning tractable, this design actually alleviates existing tensions between performance and interpretability. We call the framework JUNIPR: "Jets from UNsupervised Interpretable PRobabilistic models". In this approach, the set of particle momenta composing a jet are clustered into a binary tree that the neural network examines sequentially. Training is unsupervised and unrestricted: the network could decide that the data bears little correspondence to the chosen tree structure. However, when there is a correspondence, the network's output along the tree has a direct physical interpretation. JUNIPR models can perform discrimination tasks, through the statistically optimal likelihood-ratio test, and they permit visualizations of discrimination power at each branching in a jet's tree. Additionally, JUNIPR models provide a probability distribution from which events can be drawn, providing a data-driven Monte Carlo generator. As a third application, JUNIPR models can reweight events from one (e.g. simulated) data set to agree with distributions from another (e.g. experimental) data set.

    hep-phstat.MLEPJC(2019)·136 citations
14. 14*

    The Three-loop Quark Jet Function

    Robin Brüser🇩🇪 · Ze Long Liu🇩🇪 · Maximilian Stahlhofen🇩🇪

    We calculate the massless quark jet function to three-loop order. The quark jet function is a universal ingredient in SCET factorization for many collider and decay processes with quark initiated final state jets. Our three-loop result contributes to the resummation for observables probing the invariant mass of final state quark jets at N${}^3$LL${}^{\prime }$. It represents the first complete three-loop result for a factorization ingredient describing collinear radiation. Furthermore it constitutes a major component of the $N$-jettiness subtraction/slicing method at N${}^3$LO, which eventually may enable the calculation of fully-differential cross sections with a colorful final state at this order.

    hep-phhep-thPRL(2018)·95 citations
15. 15*

    Photons coming from an opaque obstacle as a manifestation of heavy neutrino decays

    Matias Reynoso🇦🇷 · Ismael Romero🇦🇷 · Oscar A. Sampayo🇦🇷

    Within the framework of physics beyond the standard model we study the possibility that mesons produced in the atmosphere by the cosmic ray flux, decay to heavy Majorana neutrino and these mostly to photons in the low mass region. We study the photon flux produced by sterile Majorana neutrinos ($N$) decaying after passing through a massive and opaque object such as a mountain. In order to model the production of $N$'s in the atmosphere and their decay to photons, we consider the interaction between the Majorana neutrinos and the standard matter as modeled by an effective theory. We then calculate the heavy neutrino flux originated by the decay of mesons in the atmosphere. The surviving photon flux, originated by $N$ decays, is calculated using transport equations that include the effects of Majorana neutrino production and decay.

    hep-phPRD(2018)·0 citations
16. 16*

    Behavior of axion-like particles in smoothed out domain-like magnetic fields

    Giorgio Galanti🇮🇹 · Marco Roncadelli🇮🇹

    Basically, in certain circumstances axion-like particles (ALPs) substantially enhance the photon survival probability $P_{\gamma \to \gamma }(\mathcal{E})$ of a beam emitted by a far-away source through the mechanism of photon-ALP oscillation ($\mathcal{E}$ denotes the energy). But in order for this to work, an external magnetic field $\mathbf{B}$ must be present. In several cases $\mathbf{B}$ is modeled as a domain-like network with `sharp edges': all domains have the same size $L_{\mathrm{dom}}$ (set by the $\mathbf{B}$ coherence length) and the same strength B, but the direction of $\mathbf{B}$ changes randomly and abruptly from one domain to the next. It is obviously a highly mathematical idealization wherein the components of $\mathbf{B}$ are discontinuous across the edges (whence the name sharp edges). It is therefore highly desirable to go a step further, and to find out what happens when the edges are smoothed out, namely when the abrupt change of $\mathbf{B}$ is replaced by a smooth one. Moreover, this step becomes compelling when the photon-ALP oscillation length $l_{\mathrm{osc}}$ turns out to be comparable to -- or smaller than -- $L_{\mathrm{dom}}$, because in this case the photon survival probability $P_{\gamma \to \gamma }(\mathcal{E})$ critically depends on the domain shape. In the present paper we propose a smoothed out version of the previous domain-like structure of $\mathbf{B}$ which incorporates the above changes, and we work out its implications. Even in the present case we are able to solve analytically and exactly the photon/ALP beam propagation equation inside a single smoothed-out domain, thereby evaluating the corresponding $P_{\gamma \to \gamma }(\mathcal{E})$ exactly. Our results is of particular importance in view of the new generation of gamma-ray detectors, since in such a situation $l_{\mathrm{osc}}\lesssim L_{\mathrm{dom}}$ occurs just above the TeV scale.

    ↳ astro-ph.HEhep-phPRD(2018)·62 citations
17. 17*

    Sensitivity of Neutrino-Nucleus Interaction Measurements to 2p2h Excitations

    Stephen Dolan🇫🇷 · Ulrich Mosel🇩🇪 · Kai Gallmeister🇩🇪 · Luke Pickering🇺🇸 · Sara Bolognesi🇫🇷

    We calculate the charged-current cross sections obtained at the T2K off-axis near detector for ${\nu }_{\mu }$-induced events without pions and any number of protons in the final state using transport theory as encoded in the GiBUU model. In a comparison with recent T2K data the strength of the 2p2h multinucleon correlations is determined. Linking this to the isospin (T) of the initial nuclear state, it is found that T=0 leads to a significantly better fit of the recent cross sections obtained by T2K, thus achieving consistency of the 2p2h multi-nucleon correlation contributions between electron-nucleus and neutrino-nucleus reactions.

    ↳ hep-exhep-phnucl-exnucl-thPRC(2018)·37 citations
18. 18*

    Amplification of gravitational motion via Quantum weak measurement

    Kiyoharu Kawana🇯🇵 · Daiki Ueda🇯🇵

    We investigate a new experimental possibility of measuring the Newtonian gravitational constant $G$ by using the weak measurement. Amplification via weak measurement is one of the interesting phenomena of quantum mechanics. In this letter, we consider it in a system consisting of many cold atoms which are gravitationally interacting with an external macroscopic source and show that it is possible to obtain $\mathcal{O}(10^3)$ amplification of their relative motion compared with the classical motion when the number of atoms are $\mathcal{O}(10^{15})$ and the observing time is $\sim 0.5$s. This result suggests that it might be possible to use this system as a new experimental set up for determining $G$. Besides, our study indicates that the gravitational force can behave as a repulsive force because of the weak measurement.

    ↳ quant-phcond-mat.quant-gasgr-qchep-ph+1PTEP(2019)·3 citations
19. 19*

    Exploring the applicability of dissipative fluid dynamics to small systems by comparison to the Boltzmann equation

    K. Gallmeister🇩🇪 · H. Niemi🇩🇪 · C. Greiner🇩🇪 · D. H. Rischke🇩🇪

    [Background] Experimental data from heavy-ion experiments at RHIC-BNL and LHC-CERN are quantitatively described using relativistic fluid dynamics. Even p+A and p+p collisions show signs of collective behavior describable in the same manner. Nevertheless, small system sizes and large gradients strain the limits of applicability of fluid-dynamical methods. [Purpose] The range of applicability of fluid dynamics for the description of the collective behavior, and in particular of the elliptic flow, of small systems needs to be explored. [Method] Results of relativistic fluid-dynamical simulations are compared with solutions of the Boltzmann equation in a longitudinally boost-invariant picture. As initial condition, several different transverse energy-density profiles for equilibrated matter are investigated. [Results] While there is overall a fair agreement of energy- and particle-density profiles, components of the shear-stress tensor are more sensitive to details of the implementation. The highest sensitivity is exhibited by quantities influenced by properties of the medium at freeze-out. [Conclusions] For some quantities, like the shear-stress tensor, agreement between fluid dynamics and transport theory extends into regions of Knudsen numbers and inverse Reynolds numbers where relativistic fluid dynamics is believed to fail.

    ↳ nucl-thhep-phPRC(2018)·22 citations
20. 20*

    Polarised Drell-Yan results from COMPASS

    Celso Franco (on behalf of the COMPASS collaboration)🇵🇹

    The COMPASS experiment at CERN is one of the leading experiments studying the nucleon spin structure. Until 2012 the Parton Distribution Functions and the Transverse Momentum Dependent Parton Distribution Functions (TMDs) were extensively studied at COMPASS using Semi-Inclusive Deep Inelastic Scattering measurements. In 2015, the Drell-Yan measurements with a negative pion beam interacting with a transversely polarized ammonia target have started and will be continued through 2018. The goal is to access the TMDs of both pions and protons without any prior knowledge about fragmentation functions. Since the Drell-Yan data cover the same kinematic region of the semi-inclusive data, COMPASS has the unique opportunity to test the sign change of the Sivers TMD as predicted by QCD. In this talk the first measurement of spin dependent azimuthal asymmetries in the pion induced Drell-Yan process will be presented. These asymmetries, which are related to the convolution of pion and nucleon TMDs, are extracted from pairs of oppositely charged muons with invariant masses between 4.3 GeV$c^2$ and 8.5 GeVc${}^2$

    ↳ hep-exhep-ph2 citations
21. 21*

    New relations for graviton-matter amplitudes

    Jan Plefka🇩🇪 · Wadim Wormsbecher🇩🇪

    We present new relations for scattering amplitudes of color ordered gluons, massive quarks and scalars minimally coupled to gravity. Tree-level amplitudes of arbitrary matter and gluon multiplicities involving one graviton are reduced to partial amplitudes in QCD or scalar QCD. The obtained relations are a direct generalization of the recently found Einstein-Yang-Mills relations. The proof of the new relation employs a simple diagrammatic argument trading the graviton-matter couplings to an `upgrade' of a gluon coupling with a color-kinematic replacement rule enforced. The use of the Melia-Johansson-Ochirov color basis is a key element of the reduction. We comment on the generalization to multiple gravitons in the single color trace case.

    ↳ hep-thhep-phPRD(2018)·18 citations
22. 22*

    Asymptotic freedom in $Z_2$-Yukawa-QCD models

    Holger Gies🇩🇪 · René Sondenheimer🇩🇪 · Alessandro Ugolotti🇩🇪 · Luca Zambelli🇩🇪

    $Z_2$-Yukawa-QCD models are a minimalistic model class with a Yukawa and a QCD-like gauge sector that exhibits a regime with asymptotic freedom in all its marginal couplings in standard perturbation theory. We discover the existence of further asymptotically free trajectories for these models by exploiting generalized boundary conditions. We construct such trajectories as quasi-fixed points for the Higgs potential within different approximation schemes. We substantiate our findings first in an effective-field-theory approach, and obtain a comprehensive picture using the functional renormalization group. We infer the existence of scaling solutions also by means of a weak-Yukawa-coupling expansion in the ultraviolet. In the same regime, we discuss the stability of the quasi-fixed point solutions for large field amplitudes. We provide further evidence for such asymptotically free theories by numerical studies using pseudo-spectral and shooting methods.

    ↳ hep-thhep-phEPJC(2019)·15 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.