Particle Candidates Research Articles

Axion isocurvature perturbations in low-scale models of hybrid inflation

The quantum chromodynamics (QCD) axion solves the strong $CP$ problem and represents an attractive particle candidate for cold dark matter (CDM). However, quantum fluctuations of the axion field during inflation easily result in large CDM isocurvature perturbations that are in conflict with observations of the cosmic microwave background. In this paper, we demonstrate how this problem can be solved in low-scale models of hybrid inflation that may emerge from supersymmetric grand unified theories. We consider both F-term hybrid inflation and D-term hybrid inflation in supergravity, explicitly taking into account the effect of hidden-sector supersymmetry breaking. We discuss the production of cosmic strings and show how the soft terms in the scalar potential readily allow us to achieve the correct scalar spectral index. In both cases, we are able to identify large regions in parameter space that are consistent with all constraints. In particular, we find that evading the CDM isocurvature constraint always requires a small Yukawa or gauge coupling of $\mathcal{O}({10}^{\ensuremath{-}3})$ or smaller. This translates into upper bounds on the gravitino mass of $\mathcal{O}({10}^{5})\text{ }\text{ }\mathrm{GeV}$ in F-term hybrid inflation and $\mathcal{O}({10}^{9})\text{ }\text{ }\mathrm{GeV}$ in D-term hybrid inflation. Our results point to interesting scenarios in well-motivated parameter regions that will be tested in future axion and cosmic microwave background experiments.

Asymmetric Adaptive Particle Refinement in SPH and Its Application in Soil Cutting Problems

In this study, a novel asymmetric adaptive particle refinement algorithm in smoothed particle hydrodynamics (SPH) is developed for soil cutting problems. Each candidate particle that located at the cutting blade of the structure is split into two “children” particles to minimize the oscillation of the contact force. And thus reduce the local instability. To minimize the density refinement error, a numerical method to determine the optimal smoothing lengths for “children” particles is given. To verify the accuracy of proposed algorithm, the adaptive refinement procedure are implemented into two models: one for soil cutting test on plane strain condition and the other for sample drilling test on axisymmetric condition. The observed flow pattern of the soil and contact forces are compared with laboratory experimental data available in the literature. Results indicate that the proposed asymmetric adaptive refinement algorithm could significantly avoid severe local instability and contributes to high-accuracy simulation.

Phenomenological consequences of superfluid dark matter with baryon-phonon coupling

Recently, a new form of dark matter has been suggested to naturally reproduce the empirically successful aspects of Milgrom's law in galaxies. The dark matter particle candidates are axion-like, with masses of order eV and strong self-interactions. They Bose-Einstein condense into a superfluid phase in the central regions of galaxy halos. The superfluid phonon excitations in turn couple to baryons and mediate an additional long-range force. For a suitable choice of the superfluid equation of state, this force can mimic Milgrom's law. In this paper we develop in detail some of the main phenomenological consequences of such a formalism, by revisiting the expected dark matter halo profile in the presence of an extended baryon distribution. In particular, we show how rotation curves of both high and low surface brightness galaxies can be reproduced, with a slightly rising rotation curve at large radii in massive high surface brightness galaxies, thus subtly different from Milgrom's law. We finally point out other expected differences with Milgrom's law, in particular in dwarf spheroidal satellite galaxies, tidal dwarf galaxies, and globular clusters, whose Milgromian or Newtonian behavior depends on the position with respect to the superfluid core of the host galaxy. We also expect ultra-diffuse galaxies within galaxy clusters to have velocities slightly above the baryonic Tully-Fisher relation. Finally, we note that, in this framework, photons and gravitons follow the same geodesics, and that galaxy-galaxy lensing, probing larger distances within galaxy halos than rotation curves, should follow predictions closer to the standard cosmological model than those of Milgrom's law.

Event Topology Reconstruction in the CBM Experiment

One of the main purposes of the physics program of the future heavy ion experiment CBM (FAIR, Germany) is to understand the properties of strongly interacting matter at very high baryonic densities and to study the possibility of a phase transition to a deconfined and chirally restored phase of quark matter. The experiment will operate at high interaction rates up to 10 MHz, that requires a full event reconstruction in real time.In order to make an efficient event selection online a clean sample of particles has to be provided by the reconstruction package called First Level Event Selection (FLES). The FLES package operates in two stages. First, particles registered in the CBM detector system are reconstructed. Then short-lived particles decayed before or inside the setup are searched based on their charged and neutral daughter particles. Since the FLES package is developed to run on many-core computer architectures, the reconstruction of particles is done in parallel that provides a possibility for a global competition between particle candidates. Such a global event topology reconstruction significantly improves suppression of a combinatorial background and provides for further physics analysis a very clean sample of particles produced at different stages of heavy ion collision.The global event topology reconstruction procedure and the results of its application to simulated collisions in the CBM detector setup are presented and discussed.

Object Tracking Based On Huber Loss Function.

In this paper we present a novel visual tracking algorithm, in which object tracking is achieved by using subspace learning and Huber loss regularization in a particle filter framework. The changing appearance of tracked target is modeled by Principle Component Analysis (PCA) basis vectors and row group sparsity. This method takes advantage of the strengths of sub-space representation and explicitly takes the underlying relationship between particle candidates into consideration in the tracker. The representation of each particle is learned via the multi-task sparse learning method. Huber loss function is employed to model the error between candidates and templates, yielding robust tracking. We utilize the Alternating Direction Method of Multipliers (ADMM) to solve the proposed representation model. In experiments we tested sixty representative video sequences that reflect the specific challenges of tracking and used both qualitative and quantitative metrics to evaluate the performance of our tracker. The experiment results demonstrated that the proposed tracking algorithm achieves superior performance compared to nine state-of-the-art tracking methods.

PFS: Particle-Filter-Based Superpixel Segmentation

In this paper, we propose a particle-filter-based superpixel (PFS) segmentation method that extends the original tracking problem as a region clustering problem. The basic idea is to approximate superpixel centers by multiple particles to obtain high intra-region similarity. Specifically, we firstly use a density cluster to initialize single-group particles and introduce the association rule for mining other initial candidate particles. In propagation, particles are transferred to neighboring local regions by a moving step aiming to update local candidate particles with a lower energy cost. We evaluate all particles on the basis of their cluster similarity and estimate the largest particles as the final superpixel centers. The proposed method can locate cluster centers in diverse feature space, which alleviates the risk of a local optimum and produces better segmentation performance. Experimental results on the Berkeley segmentation 500 dataset (BSD500) demonstrate that our method outperforms seven state-of-the-art methods.

Searches for Dark Matter via Mono-W Production in Inert Doublet Model at the LHC**Supported by the National Natural Science Foundation of China under Grant Nos. 11205003, 11305001, 11575002, the Key Research Foundation of Education Ministry of Anhui Province of China under Grant Nos. KJ2017A032, KJ2016A749, KJ2013A260, and Natural Science Foundation of West Anhui University under Grant No. WXZR201614

The Inert Doublet Model (IDM) is one of the many beyond Standard Model scenarios with an extended scalar sector, which provide a suitable dark matter particle candidate. Dark matter associated visible particle production at high energy colliders provides a unique way to determine the microscopic properties of the dark matter particle. In this paper, we investigate that the mono-W + missing transverse energy production at the Large Hadron Collider (LHC), where W boson decay to a lepton and a neutrino. We perform the analysis for the signal of mono-W production in the IDM and the Standard Model (SM) backgrounds, and the optimized criteria employing suitable cuts are chosen in kinematic variables to maximize signal significance. We also investigate the discovery potential in several benchmark scenarios at the 14 TeV LHC. When the light Z2 odd scalar higgs of mass is about 65 GeV, charged Higgs is in the mass range from 120 GeV to 250 GeV, it provides the best possibility with a signal significance of about 3σ at an integrated luminosity of about 3000 fb−1.

Rapid Analysis of Cell-Nanoparticle Interactions using Single-Cell Raman Trapping Microscopy.

Iron oxide nanoparticles have been used in preclinical studies to label stem cells for non-invasive tracking and homing. The search continues for novel particle candidates that are suitable for clinical applications. Since standard analyses to investigate cell-particle interactions and safety are labor-intensive, an efficient procedure is required to guide future particle development and to exclude adverse health effects. The application of combined Raman trapping microscopy with fluidic chips is reported for the analysis of single cells labeled with different types of aminated iron oxide particles. Multivariate data analysis revealed Raman signal differences that could be clearly assigned to cell-particle interactions and cytotoxicity, respectively. A validation dataset verified that more than 95 % of the spectra were correctly classified. Thus, our approach enables rapid discrimination of non-hazardous from cytotoxic nanoparticles as a prerequisite for safe clinical applications.

Rapid Analysis of Cell–Nanoparticle Interactions using Single‐Cell Raman Trapping Microscopy

AbstractIron oxide nanoparticles have been used in preclinical studies to label stem cells for non‐invasive tracking and homing. The search continues for novel particle candidates that are suitable for clinical applications. Since standard analyses to investigate cell–particle interactions and safety are labor‐intensive, an efficient procedure is required to guide future particle development and to exclude adverse health effects. The application of combined Raman trapping microscopy with fluidic chips is reported for the analysis of single cells labeled with different types of aminated iron oxide particles. Multivariate data analysis revealed Raman signal differences that could be clearly assigned to cell–particle interactions and cytotoxicity, respectively. A validation dataset verified that more than 95 % of the spectra were correctly classified. Thus, our approach enables rapid discrimination of non‐hazardous from cytotoxic nanoparticles as a prerequisite for safe clinical applications.

Searching for spectral oscillations due to photon-axionlike particle conversion using the Fermi-LAT observations of bright supernova remnants

Axionlike-particles (ALPs) are one promising type of dark matter candidate particle that may generate detectable effects on $\gamma$-ray spectra other than the canonical weakly interacting massive particles. In this work we search for such oscillation effects in the spectra of supernova remnants caused by the photon-ALP conversion, using the Fermi Large Area Telescope data. Three bright supernova remnants, IC443, W44, and W51C, are analyzed. The inclusion of photon-ALP oscillations yields an improved fit to the $\gamma$-ray spectrum of IC443, which gives a statistical significance of $4.2\sigma$ in favor of such spectral oscillation. However, the best-fit parameters of ALPs ($m_{a}=6.6\,{\rm neV}$, $g_{a\gamma}=13.4 \times 10^{-11}\,{\rm GeV}^{-1}$) are in tension with the upper bound ($g_{a\gamma}< 6.6 \times 10^{-11}\,{\rm GeV}^{-1}$) set by the CAST experiment. It is difficult to explain the results using the systematic uncertainties of the flux measurements. We speculate that the "irregularity" displayed in the spectrum of IC443 may be due to the superposition of the emission from different parts of the remnant.

Searching for Dark Matter: Background Discrimination in the PICO detector

The PICO experiment uses superheated bubble chambers located at SNOLAB for direct detection of Weakly Interacting Massive Particles (WIMPs), one of the candidate particles for dark matter. Bubbles form in the detector when a particle interacts with a nucleus of the target fluid, and the recoiling deposits enough energy to nucleate a bubble in the superheated fluid. Much of the data analysis for PICO focuses on determining what type of particle caused a bubble to form. The differentiation is made by analysing signals from pressure sensors, piezoelectric acoustic sensors, and stereoscopic cameras. This talk will present an overview of the sensors and analysis which are used to discriminate between WIMP interactions and background events in the PICO 2L detector, with a focus on the role of image analysis and the potential sensitivity of the detector if good discrimination can be realized.

Probing dark matter signals with Einstein Probe

Determining the physical nature of dark matter is central to contemporary astrophysics and particle physics. The hypothetical sterile neutrinos with a mass of order keV are one of the most promising candidate particles for dark matter, which can play an important role in particle physics, astrophysics and cosmology. In radiative decay, a keV sterile neutrino releases an X-ray photon that has an energy half of the neutrino’s rest mass, which facilitates its indirect detection. In 2014, using stacked XMM-Newton spectra of nearby galaxy clusters, researchers reported the detection of a weak line-like feature at 3.5 keV, which was interpreted as the decaying signal of sterile neutrino dark matter. However, follow-up studies did not reach a consensus on the reality of this signal, chiefly due to the limited quality of current X-ray data. The Einstein Probe, with its unique wide-field telescopes, has the great potential of confirming or rejecting the 3.5 keV signal from nearby massive galaxies and galaxy clusters, and will effectively conduct a highly sensitive search for dark matter over the keV energy range.

Nuclear Physics with Magnetic Charges

The magnetic spinor particles (magnetic charges) are the real structural components all varieties of the Mass, for example, atoms, nucleons, positrons and neutrinos. Atomic-shaped device of Mass is the natural and the only possible organization of electric and magnetic charges which can create a gravitational field. At level of a popular language one can define nucleons as “small atoms”, and positron and neutrino as “very small atoms”. The electric and magnetic fundamental particles in neutron and proton shells which by tradition should be called quarks have charges of smaller magnitude than the charges of particles in atomic shells. Positron which participates in the gravitational interaction and, consequently, has an atomic-shaped device is the most likely candidate for the role of the proton nucleus. The most likely candidate particles on the participation in nuclei of proton and neutron as well as in nuclei of the positron and neutrino are presented in the article. So-called abnormal magnetic moment of neutron is formed by the quark magnetic dipoles which are like to unpaired electrons in the so-called magnetic atoms rotate on the outer orbitals of the neutron shell. The participation of the “magnetic electron” (magneton) in the neutrino core assumes the existence of the so-called anomalous magnetic moment and in the neutrino shell. The existence of real magnetic charges in the structures of the Mass draws our attention on such important problem as interaction between charges in the framework of electromagnetic dipoles such as and in which manifest the weak attraction. Weak interaction by its nature is electromagnetic. So-called electromagnetic interaction, manifested in pairs of homogeneous charges of opposite signs, is either electric or magnetic, but not electromagnetic. The explanation of the weak interaction in the marked pairs of charges is based on the author’s concept of the World Physical Triad and “Dark Energy”. Forces responsible for the interaction of the charges composing the electromagnetic dipoles correspond, conditionally of the weak charges of the particles which what assume mutual suppression of the influence of their fields on the Energo-medium and the formation of the weak “Dark energy”. Complex of magnetic particles, the quark magnetic dipoles and magneton by means of which the interconversion of a proton and a neutron is realized and maintained their constant number in the atomic nuclei can be called as magnetic meson. Namely, a processes of interconversion between a neutron and a proton which, as a rule, are not accompanied by secretions, created the illusion of neutron stability in atomic nuclei. The energy created by an exchange of magnetic mesons between neutron and proton can be a component of nuclear forces (strong interaction). Another effective and, most likely, the main component in the composition of the nuclear forces is the gravitational “Dark Energy”. Physics and structure of neutrinos presented in the paper suggest that the nature of these particles closer to the ideology of E. Majorana than P. Dirac’s.

Search for dark matter particle candidates produced in association with a Z boson in pp collisions at a center-of-mass energy of 13 TeV with the ATLAS detector

A search for dark matter particle candidates produced in association with a Z boson in proton-proton collisions at the total center-of-mass energy of 13 TeV is presented. The search uses 36.1 inverse femtobarn of data collected by the ATLAS experiment at the Large Hadron Collider in 2015 and 2016. Events with large missing transverse momentum and consistent with the decay of a Z boson into oppositely charged electron or muon pairs were selected in the analysis. Background estimates and corresponding systematic uncertainties are shown. Exclusion limits on the dark matter candidate and mediator masses are reported.

Limits on Axion Couplings from the First 80 Days of Data of the PandaX-II Experiment.

We report new searches for solar axions and galactic axionlike dark matter particles, using the first low-background data from the PandaX-II experiment at China Jinping Underground Laboratory, corresponding to a total exposure of about 2.7×10^{4} kg day. No solar axion or galactic axionlike dark matter particle candidate has been identified. The upper limit on the axion-electron coupling (g_{Ae}) from the solar flux is found to be about 4.35×10^{-12} in the mass range from 10^{-5} to 1 keV/c^{2} with 90%confidence level, similar to the recent LUX result. We also report a new best limit from the ^{57}Fe deexcitation. On the other hand, the upper limit from the galactic axions is on the order of 10^{-13} in the mass range from 1 to 10 keV/c^{2} with 90%confidence level, slightly improved compared with the LUX.

The Relentless Hunt for Dark Matter

The latest results from two dark matter searches have further ruled out many theoretically attractive dark matter particle candidates.

Cosmic degeneracies – II. Structure formation in joint simulations of warm dark matter and f(R) gravity

We present for the first time the outcomes of a cosmological N-body simulation that simultaneously implements a warm dark matter (WDM) particle candidate and a modified gravitational interaction in the form of f(R) gravity, and compare its results with the individual effects of these two independent extensions of the standard ΛCDM scenario, and with the reference cosmology itself. We consider a rather extreme value of the WDM particle mass (mWDM = 0.4 keV) and a single realization of f(R) gravity with |$|\bar{f}_{R0}|=10^{-5}$|⁠, and we investigate the impact of these models and of their combination on a wide range of cosmological observables with the aim to identify possible observational degeneracies. Differently from the case of combining f(R) gravity with massive neutrinos, we find that most of the considered observables do not show any significant degeneracy due to the fact that WDM and f(R) gravity are characterized by individual observational signatures with a very different functional dependence on cosmic scales and halo masses. In particular, this is the case for the non-linear matter power spectrum in real space, for the halo and subhalo mass functions, for the halo density profiles and for the concentration–mass relation. However, other observables – like e.g. the halo bias – do show some level of degeneracy between the two models, while a very strong degeneracy is observed for the non-linear matter power spectrum in redshift space, for the density profiles of small cosmic voids, and for the voids abundance as a function of the void core density.

Study of long-lived heavy charged particles produced in pp collisions at energy 13 TeV

We are interested in long-lived heavy charged particles because they would be possible SUSY particle candidats. This paper shows our preliminary results of long-lived heavy charged particles generation using PYTHIA 8. More than 107 events have been generated with pp collisions at energy in the center of mass = 13 TeV and about 3.27 105 long-lived heavy charged particles candidates have been found in the geometric acceptance of the LHCb detector. Long-lived heavy charged particles has mass 1.025 TeV/c2 and lifetime 157.7 nanoseconds, therefore they can travel throughout all subdetectors. We try not only calculate their acceptance in function of transverse momentum and rapidity but also combine a pair of candidats with opposite charge in order to reconstruct their invariant mass. In the next step, we have intention to identify stau using the informations from subdetectors such as the inner tracker and the muon chambers.

A correlative classifiers approach based on particle filter and sample set for tracking occluded target

Target tracking is one of the most important issues in computer vision and has been applied in many fields of science, engineering and industry. Because of the occlusion during tracking, typical approaches with single classifier learn much of occluding background information which results in the decrease of tracking performance, and eventually lead to the failure of the tracking algorithm. This paper presents a new correlative classifiers approach to address the above problem. Our idea is to derive a group of correlative classifiers based on sample set method. Then we propose strategy to establish the classifiers and to query the suitable classifiers for the next frame tracking. In order to deal with nonlinear problem, particle filter is adopted and integrated with sample set method. For choosing the target from candidate particles, we define a similarity measurement between particles and sample set. The proposed sample set method includes the following steps. First, we cropped positive samples set around the target and negative samples set far away from the target. Second, we extracted average Haar-like feature from these samples and calculate their statistical characteristic which represents the target model. Third, we define the similarity measurement based on the statistical characteristic of these two sets to judge the similarity between candidate particles and target model. Finally, we choose the largest similarity score particle as the target in the new frame. A number of experiments show the robustness and efficiency of the proposed approach when compared with other state-of-the-art trackers.

Search for neutrinos from dark matter self-annihilations in the center of the Milky Way with 3 years of IceCube/DeepCore

We present a search for a neutrino signal from dark matter self-annihilations in the Milky Way using the IceCube Neutrino Observatory (IceCube). In 1005 days of data we found no significant excess of neutrinos over the background of neutrinos produced in atmospheric air showers from cosmic ray interactions. We derive upper limits on the velocity averaged product of the dark matter self-annihilation cross section and the relative velocity of the dark matter particles langle sigma _{text {A}}vrangle . Upper limits are set for dark matter particle candidate masses ranging from 10 GeV up to 1 TeV while considering annihilation through multiple channels. This work sets the most stringent limit on a neutrino signal from dark matter with mass between 10 and 100 GeV, with a limit of 1.18cdot 10^{-23}text { cm}^3text {s}^{-1} for 100 GeV dark matter particles self-annihilating via tau ^+tau ^- to neutrinos (assuming the Navarro–Frenk–White dark matter halo profile).