Thu·Jun 11, 2020Thursday·June 11, 2020

1. 01*

   Finding New Physics without learning about it: Anomaly Detection as a tool for Searches at Colliders

   M. Crispim Romao🇵🇹 · N. F. Castro🇵🇹 · R. Pedro🇵🇹

   In this paper we propose a new strategy, based on anomaly detection methods, to search for new physics phenomena at colliders independently of the details of such new events. For this purpose, machine learning techniques are trained using Standard Model events, with the corresponding outputs being sensitive to physics beyond it. We explore three novel AD methods in HEP: Isolation Forest, Histogram Based Outlier Detection, and Deep Support Vector Data Description; alongside the most customary Autoencoder. In order to evaluate the sensitivity of the proposed approach, predictions from specific new physics models are considered and compared to those achieved when using fully supervised deep neural networks. A comparison between shallow and deep anomaly detection techniques is also presented. Our results demonstrate the potential of semi-supervised anomaly detection techniques to extensively explore the present and future hadron colliders' data.

   hep-phphysics.comp-phEPJC(2021)·74 citations
2. 02*

   Unravelling the richness of dark sector by FASER$\nu$

   Pouya Bakhti🇮🇷 · Yasaman Farzan🇮🇷 · Silvia Pascoli🇬🇧

   FASER$\nu$ is a newly proposed experiment which will take data in run III of the LHC during 2021-2023. It will be located in front of the FASER detector, 480~m away from the ATLAS interaction point in the forward direction. Its main goal is to detect neutrinos of all flavors produced at the interaction point with superb precision in reconstructing charged tracks. This capability makes FASER$\nu$ an ideal setup for uncovering the pattern and properties of a light dark sector. We demonstrate this capability for a well-motivated class of models with a dark matter candidate of mass around a few GeV. Dark matter annihilates to a pair of intermediate neutral particles that subsequently decay into the standard model charged fermions. We show how FASER$\nu$ can shed light on the structure of the dark sector by unravelling the decay chain within such models.

   hep-phhep-exJHEP(2020)·11 citations
3. 03*

   Atomki anomaly in gauged $U(1{)}_R$ symmetric model

   Osamu Seto🇯🇵 · Takashi Shimomura🇯🇵

   The Atomki collaboration has reported that unexpected excesses have been observed in the rare decays of Beryllium nucleus. It is claimed that such excesses can suggest the existence of a new boson, called $X$, with the mass of about $17$ MeV. To solve the Atomki anomaly, we consider a model with gauged $U(1{)}_R$ symmetry and identify the new gauge boson with the $X$ boson. We also introduce two $SU(2)$ doublet Higgs bosons and one singlet Higgs boson, and discuss a very stringent constraint from neutrino-electron scattering. It is found that the $U(1{)}_R$ charges of the doublet scalars are determined to evade the constraint. In the end, we find the parameter region in which the Atomki signal and all experimental constraints can be simultaneously satisfied.

   hep-phJHEP(2021)·27 citations
4. 04*

   DiffExp, a Mathematica package for computing Feynman integrals in terms of one-dimensional series expansions

   Martijn Hidding🇮🇪

   DiffExp is a Mathematica package for integrating families of Feynman integrals order-by-order in the dimensional regulator from their systems of differential equations, in terms of one-dimensional series expansions along lines in phase-space, which are truncated at a given order in the line parameter. DiffExp is based on the series expansion strategies that were explored in recent literature for the computation of families of Feynman integrals relevant for Higgs plus jet production with full heavy quark mass dependence at next-to-leading order. The main contribution of this paper, and its associated package, is to provide a public implementation of these series expansion methods, which works for any family of integrals for which the user provides a set of differential equations and boundary conditions (and for which the program is not computationally constrained.) The main functions of the DiffExp package are discussed, and its use is illustrated by applying it to the three loop equal-mass and unequal-mass banana graph families.

   hep-phhep-thComput.Phys.Commun.(2021)·228 citations
5. 05*

   $B$-meson Ioffe-time distribution amplitude at short distances

   Shuai Zhao🇺🇸 · Anatoly V. Radyushkin🇺🇸

   We propose the approach for a lattice investigation of light-cone distribution amplitudes (LCDA) of heavy-light mesons, such as the $B$-meson, using the formalism of parton pseudo-distributions. A basic ingredient of the approach is the study of short-distance behavior of the $B$-meson Ioffe-time distribution amplitude (ITDA), which is a generalization of the $B$-meson LCDA in coordinate space. We construct a reduced ITDA for the $B$-meson, and derive the matching relation between the reduced ITDA and the LCDA. The reduced ITDA is ultraviolet finite, which guarantees that the continuum limit exists on the lattice.

   hep-phhep-latPRD(2021)·24 citations
6. 06*

   Lepto-Axiogenesis

   Raymond T. Co🇺🇸 · Nicolas Fernandez🇺🇸 · Akshay Ghalsasi🇺🇸 · Lawrence J. Hall🇺🇸 · Keisuke Harigaya🇺🇸

   We propose a baryogenenesis mechanism that uses a rotating condensate of a Peccei-Quinn (PQ) symmetry breaking field and the dimension-five operator that gives Majorana neutrino masses. The rotation induces charge asymmetries for the Higgs boson and for lepton chirality through sphaleron processes and Yukawa interactions. The dimension-five interaction transfers these asymmetries to the lepton asymmetry, which in turn is transferred into the baryon asymmetry through the electroweak sphaleron process. QCD axion dark matter can be simultaneously produced by dynamics of the same PQ field via kinetic misalignment or parametric resonance, favoring an axion decay constant $f_a\lesssim 10^{10}$ GeV, or by conventional misalignment and contributions from strings and domain walls with $f_a\sim 10^{11}$ GeV. The size of the baryon asymmetry is tied to the mass of the PQ field. In simple supersymmetric theories, it is independent of UV parameters and predicts the supersymmtry breaking mass scale to be $\mathcal{O}(10-10^4)$ TeV, depending on the masses of the neutrinos and whether the condensate is thermalized during a radiation or matter dominated era. We also construct a theory where TeV scale supersymmetry is possible. Parametric resonance may give warm axions, and the radial component of the PQ field may give signals in rare kaon decays from mixing with the Higgs and in dark radiation.

   hep-phastro-ph.COJHEP(2021)·101 citations
7. 07*

   The weak $B$, $B_s$ and $B_c$ decays to radially excited states

   Tian Zhou🇨🇳 · Tianhong Wang🇨🇳 · Yue Jiang🇨🇳 · Lei Huo🇨🇳 · Guo-Li Wang🇨🇳

   Recently, many new excited states of heavy mesons, especially the radially excited states, are discovered. The study of the production processes of these states from the ground b-flavored mesons is of interest. In this paper, we use the improved Bethe-Salpeter method to study the semi-leptonic and non-leptonic decays of $B$, $B_s$, and $B_c$ mesons, where the final states are focused on the radial excited $2S$ and $3S$ states. We find that many channels have branching ratios up to $10^{-4}$, which are within the detection accuracy of current experiments.

   hep-phJ.Phys.G(2021)·11 citations
8. 08*

   $A_0$ condensation, Nielsen's identity and effective potential of order parameter

   Vladimir Skalozub🇺🇦

   In high temperature SU(2) gluodynamics, the condensation of the zero component gauge field potential A_0 =const and its gauge-fixing dependence are investigated. A_0 is mutually related with Polyakov's loop <L>. The two-loop effective potential W(A_0,xi) is recalculated in the background relativistic R_xi gauge. It depends on the parameter xi, has a nontrivial minimum and satisfies Nielsen's identity. These signs mean gauge invariance of the condensation phenomenon. Following the idea of Belyaev, we express W(A_0,xi) in terms of <L>. The obtained effective potential of order parameter differs from that derived by this author. It is independent of xi and has a nontrivial minimum position. Hence the A_0 condensation follows. We show that the equation relating A_0 and (A_0)|_(classical) coincides with the special characteristic orbit in the (A)$-plain along which the W(A_0,xi) is xi-independent. In this way the link between these two gauge invariant descriptions is established. The minimum value of the Polyakov loop is calculated. Comparison with results of other authors is given.

   hep-phPhys.Part.Nucl.Lett.(2021)·5 citations
9. 09*

   Determination of generalized parton distributions through a simultaneous analysis of axial form factor and wide-angle Compton scattering data

   Hadi Hashamipour🇮🇷 · Muhammad Goharipour🇮🇷 · Siamak S. Gousheh🇮🇷

   In this work, we present a new set of unpolarized ($H$) and polarized ($\tilde{H}$) generalized parton distributions (GPDs) that have been determined using a simultaneous ${\chi }^2$ analysis of the nucleon axial form factor (AFF) and wide-angle Compton scattering (WACS) experimental data at the next-to-leading order (NLO) accuracy in QCD. We explore various Ansatzes presented in the literature for GPDs, which use forward parton distributions as input, and choose the ones most suited to our analysis. The experimental data included in our analysis cover a wide range of the squared transverse momentum, which is $0.025<-t<6.46$ GeV${}^2$. We show that the WACS data affect significantly the large $-t$ behavior of $\tilde{H}$. The polarized GPDs obtained from the simultaneous analysis of AFF and WACS data differ considerably from the corresponding ones obtained by analyzing AFF and WACS separately, and have less uncertainties. We show that the theoretical predictions obtained using our GPDs are in good agreement with the analyzed AFF and WACS data for the entire range of $-t$ studied. Finally, we obtain the impact parameter dependent parton distributions, both in an unpolarized and in a transversely polarized proton, and present them as tomography plots.

   hep-phPRD(2020)·17 citations
10. 10*

    On a chi^2-function with previously estimated background

    Fernando M.L. Almeida Jr.🇧🇷 · Andre A. Nepomuceno🇧🇷

    There are intensive efforts searching for new phenomena in many present and future scientific experiments such as LHC at CERN, CLIC, ILC and many others. These new signals are usually rare and frequently contaminated by many different background events. Starting from the concept of profile likelihood we obtain what can be called a profile ${\chi }^2$-function for counting experiments which has no background parameters to be fitted. Signal and background statistical fluctuations are automatically taking in account even when the content of some bins are zero. This paper analyzes the profile ${\chi }^2$-function for fitting binned data in counting experiment when signal and background events obey Poisson statistics. The background events are estimated previously, either by Monte Carlo events, ``idle" run events or any other reasonable way. The here studied method applies only when the background and signal are completely independent events, i.e, they are non-coherent events. The profile ${\chi }^2$-function has shown to have a fast convergence, with fewer events, to the ``true'' values for counting experiments as shown in MC toy tests. It works properly even when the bin contents are low and also when the signal to background ratio is small. Other interesting points are also presented and discussed. One of them is that the background parameter does not need to be estimated with very high precision even when there are few signal events during a fitting procedure. An application to Higgs boson discovery is discussed using previously published ATLAS/LHC experiment data.

    hep-phhep-exnucl-exphysics.data-anBraz.J.Phys.(2020)·0 citations
11. 11*

    Chiral theory of nucleons and pions in the presence of an external gravitational field

    H. Alharazin🇩🇪 · D. Djukanovic🇩🇪 · J. Gegelia🇩🇪 · M. V. Polyakov🇩🇪

    We extend the standard second order effective chiral Lagrangian of pions and nucleons by considering the coupling to an external gravitational field. As an application we calculate one-loop corrections to the one-nucleon matrix element of the energy-momentum tensor to fourth order in chiral counting, and next-to-leading order tree-level amplitude of the pion-production in an external gravitational field. We discuss the relation of the obtained results to experimentally measurable observables. Our expressions for the chiral corrections to the nucleon gravitational form factors differ from those in the literature. That might require to revisit the chiral extrapolation of the lattice data on the nucleon gravitational form factors obtained in the past.

    hep-phhep-latnucl-thPRD(2020)·46 citations
12. 12*

    Thermal properties of $\pi$ and $\rho$ meson

    Fei Gao🇩🇪 · Minghui Ding🇮🇹

    We computed the pole masses and decay constants of $\pi$ and $\rho$ meson at finite temperature in the framework of Dyson-Schwinger equations and Bethe-Salpeter equations approach. Below transition temperature, pion pole mass increases monotonously, while $\rho$ meson seems to be temperature independent. Above transition temperature, pion mass approaches the free field limit, whereas $\rho$ meson is about twice as large as that limit. Pion and the longitudinal projection of $\rho$ meson decay constants have similar behaviour as the order parameter of chiral symmetry, whereas the transverse projection of $\rho$ meson decay constant rises monotonously as temperature increases. The inflection point of decay constant and the chiral susceptibility get the same phase transition temperature. Though there is no access to the thermal width of mesons within this scheme, it is discussed by analyzing the Gell-Mann-Oakes-Renner (GMOR) relation in medium. These thermal properties of hadron observables will help us understand the QCD phases at finite temperature and can be employed to improve the experimental data analysis and heavy ion collision simulations.

    hep-phnucl-thEPJC(2020)·15 citations
13. 13*

    Neutrino Floor in Leptophilic $U(1)$ Models: Modification in $U(1{)}_{L_{\mu }-L_{\tau }}$

    Soumya Sadhukhan🇮🇳 · Manvinder Pal Singh🇮🇳

    In this work, we investigate the beyond standard model (BSM) impact of leptophilic U(1) models, namely $U(1{)}_{L_{\mu }-L_e}$, $U(1{)}_{L_e-L_{\tau }}$ and $U(1{)}_{L_{\mu }-L_{\tau }}$ on coherent elastic neutrino-nucleus scattering (CE$\nu$NS) and hence its effect on dark matter (DM) direct detection experiments. Imposing the latest relevant experimental constraints on these models, we obtain $\mathcal{O}(50\%)$ enhancement for case of $U(1{)}_{L_{\mu }-L_{\tau }}$ in a region $m_Z^{\prime }\approx 20$MeV. Subsequently, we observe that the enhancement seen in CE$\nu$NS is roughly getting translated to enhancement by a factor of 2.7 (for Germanium based detectors) and 1.8 (for Xenon based detectors) in the neutrino scattering event rate which eventually enhances the neutrino floor by same amount. This enhancement is more prominent in the region with DM masses less than 10 GeV. The model parameter space that leads to this enhancement, can simultaneously explain both anomalous magnetic moment of muon ($(g-2{)}_{\mu }$) and observed DM relic density, in a modified scenario. Enhancement of neutrino floor requires increased number of DM-nucleon scattering events in the future DM direct detection experiments, to establish themselves to be DM signal events. In absence of any DM signal, those experiments can directly be used to measure the neutrino rate, quantifying the BSM effects.

    hep-phPRD(2021)·15 citations
14. 14*

    Kaon decays shedding light on massless dark photons

    Jhih-Ying Su🇹🇼 · Jusak Tandean🇹🇼

    We explore kaon decays with missing energy carried away by a massless dark photon, $\bar{\gamma }$, assumed to have flavor-changing dipole-type couplings to the $d$ and $s$ quarks. We consider in particular the neutral-kaon modes $K_L\to \gamma \bar{\gamma }$ and $K_L\to {\pi }^0\gamma \bar{\gamma }$ and their $K_S$ counterparts, as well as the charged-kaon channel $K^{+}\to {\pi }^{+}\gamma \bar{\gamma }$, each of which also has an ordinary photon, $\gamma$, in the final state. In addition, we look at $K_{L,S}\to {\pi }^{+}{\pi }^{-}\bar{\gamma }$ and $K^{+}\to {\pi }^{+}{\pi }^0\bar{\gamma }$. Interestingly, the same $ds\bar{\gamma }$ interactions give rise to the flavor-changing two-body decays of hyperons with missing energy and are subject to model-independent constraints that can be inferred from the existing hyperon data. Taking this into account, we obtain branching fractions $\mathcal{B}(K_L\to \gamma \bar{\gamma })$ and $\mathcal{B}(K_L\to {\pi }^0\gamma \bar{\gamma })$ which can be as high as $10^{-3}$ and $10^{-6}$, respectively, one or both of which may be within the sensitivity reach of the KOTO experiment. Furthermore, we find that $\mathcal{B}(K^{+}\to {\pi }^{+}\gamma \bar{\gamma })$ and $\mathcal{B}(K^{+}\to {\pi }^{+}{\pi }^0\bar{\gamma })$ are allowed to be maximally of order $10^{-6}$ as well, which may be probed by NA62. Complementarily, the hyperon modes can have rates which are potentially accessible by BESIII. Thus, these ongoing experiments could soon be able to offer significant tests on the existence of the massless dark photon.

    hep-phhep-exEPJC(2020)·18 citations
15. 15*

    HiggsBounds-5: Testing Higgs Sectors in the LHC 13 TeV Era

    Philip Bechtle🇩🇪 · Daniel Dercks🇩🇪 · Sven Heinemeyer🇪🇸 · Tobias Klingl🇩🇪 · Tim Stefaniak🇩🇪 · Georg Weiglein🇩🇪 · Jonas Wittbrodt🇸🇪

    We describe recent developments of the public computer code HiggsBounds. In particular, these include the incorporation of LHC Higgs search results from Run 2 at a center-of-mass energy of 13 TeV, and an updated and extended framework for the theoretical input that accounts for improved Higgs cross section and branching ratio predictions and new search channels. We furthermore discuss an improved method used in HiggsBounds to approximately reconstruct the exclusion likelihood for LHC searches for non-standard Higgs bosons decaying to $\tau \tau$ final states. We describe in detail the new and updated functionalities of the new version HiggsBounds-5.

    hep-phhep-exEPJC(2020)·380 citations
16. 16*

    Frame Covariant Formalism for Fermionic Theories

    Kieran Finn🇬🇧 · Sotirios Karamitsos🇬🇧 · Apostolos Pilaftsis🇬🇧

    We present a frame- and reparametrisation-invariant formalism for quantum field theories that include fermionic degrees of freedom. We achieve this using methods of field-space covariance and the Vilkovisky-DeWitt (VDW) effective action. We explicitly construct a field-space supermanifold on which the quantum fields act as coordinates. We show how to define field-space tensors on this supermanifold from the classical action that are covariant under field reparametrisations. We then employ these tensors to equip the field-space supermanifold with a metric, thus solving a long-standing problem concerning the proper definition of a metric for fermionic theories. With the metric thus defined, we use well-established field-space techniques to extend the VDW effective action and express any fermionic theory in a frame- and field-reparametrisation-invariant manner.

    ↳ hep-thhep-phEPJC(2021)·42 citations
17. 17*

    Observing the fate of the false vacuum with a quantum laboratory

    Steven Abel🇬🇧 · Michael Spannowsky🇬🇧

    We design and implement a quantum laboratory to experimentally observe and study dynamical processes of quantum field theories. Our approach encodes the field theory as an Ising model, which is then solved by a quantum annealer. As a proof-of-concept, we encode a scalar field theory and measure the probability for it to tunnel from the false to the true vacuum for various tunnelling times, vacuum displacements and potential profiles. The results are in accord with those predicted theoretically, showing that a quantum annealer is a genuine quantum system that can be used as a quantum laboratory. This is the first time it has been possible to experimentally measure instanton processes in a freely chosen quantum field theory. This novel and flexible method to study the dynamics of quantum systems can be applied to any field theory of interest. Experimental measurements of the dynamical behaviour of field theories are independent of theoretical calculations and can be used to infer their properties without being limited by the availability of suitable perturbative or nonperturbative computational methods. In the near future, measurements in such a quantum laboratory could therefore be used to improve theoretical and computational methods conceptually and may enable the measurement and detailed study of previously unobserved quantum phenomena.

    ↳ hep-thhep-phquant-phPRX Quantum(2021)·69 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.