The First Year of the Large Hadron Collider: A Brief Review

The first year of LHC data taking provided an integrated luminosity of about 35/pb in proton-proton collisions at sqrt(s)=7 TeV. The accelerator and the experiments have demonstrated an excellent performance. The experiments have obtained important physics results in many areas, ranging from tests of the Standard Model to searches for new particles. Among other results the physics highlights have been the measurements of the W-, Z-boson and t t-bar production cross-sections, improved limits on supersymmetric and other hypothetical particles and the observation of jet-quenching, elliptical flow and J/Psi suppression in lead-lead collisions at sqrt(sNN) = 2.76 TeV.Comment: 11 pages, 9 figures, invited brief review for Mod. Phys. Lett.

Sentence context prevails over word association in aphasia patients with spared comprehension : evidence from N400 event-related potential

Behavioral and event-related potential (ERP) studies on aphasia patients showed that lexical information is not lost but rather its integration into the working context is hampered. Studies have been conducted on the processing of sentence-level information (meaningful versus meaningless) and of word-level information (related versus unrelated) in aphasia patients, but we are not aware of any study that assesses the relationship between the two. In healthy subjects the processing of a single word in a sentence context has been studied using the N400 ERP. It was shown that, even when there is only a weak expectation of a final word in a sentence, this expectation will dominate word relatedness. In order to study the effect of semantic relatedness between words in sentence processing in aphasia patients, we conducted a crossed design ERP study, crossing the factors of word relatedness and sentence congruity. We tested aphasia patients with mild to minimum comprehension deficit and healthy young and older (age-matched with our patients) controls on a semantic anomaly judgment task when simultaneously recording EEG. Our results show that our aphasia patient's N400 amplitudes in response to the sentences of our crossed-design study were similar to those of our age-matched healthy subjects. However, we detected an increase in the N400 ERP latency in those patients, indicating a delay in the integration of the new word into the working context. Additionally, we observed a positive correlation between comprehension level of those patients and N400 effect in response to meaningful sentences without word relatedness contrasted to meaningless sentences without word relatedness

Ponderomotive scattering of an electron-bunch before injection into a laser wakefield

For the purpose of laser wakefield acceleration, it turned out that also the injection of electron bunches longer than a plasma wavelength can generate accelerated femtosecond bunches with relatively low energy spread. This is of high interest because such injecting bunches can be provided, e.g., by state-of-the-art photo cathode RF guns. Here we point out that when an e-bunch is injected in the wakefield it is important to take into account the ponderomotive scattering of the injecting bunch by the laser pulse in the vacuum region located in front of the plasma. At low energies of the injected bunch this scattering results in a significant drop of the collection efficiency. Larger collection efficiency can by reached with lower intensity laser pulses and relatively high injection energies. We also estimate the minimum trapping energy for the injected electrons and the length of the trapped bunch.Comment: 12 pages, 5 figures, submitted to Phys. Rev.

Gradient boosting decision trees classification of blazars of uncertain type in the fourth Fermi-LAT catalog

The deepest all-sky survey available in the $\gamma$-ray band - the last release of the Fermi-LAT catalogue (4FGL-DR3) based on the data accumulated in 12 years, contains more than 6600 sources. The largest population among the sources is blazar subclass - 3743, $60.1\%$ of which are classified as BL Lacertae objects (BL Lacs) or Flat Spectrum Radio Quasars (FSRQs), while the rest are listed as blazar candidates of uncertain type (BCU) as their firm optical classification is lacking. The goal of this study is to classify BCUs using different machine learning algorithms which are trained on the spectral and temporal properties of already classified BL Lacs and FSRQs. Artificial Neural Networks, \textit{XGBoost} and LightGBM algorithms are employed to construct predictive models for BCU classification. Using 18 input parameters of 2219 BL Lacs and FSRQs, we train (80\% of the sample) and test (20\%) these algorithms and find that LightGBM model, state-of-the-art classification algorithm based on gradient boosting decision trees, provides the highest performance. Based on our best model, we classify 825 BCUs as BL Lac candidates and 405 as FSRQ candidates, however, 190 remain without a clear prediction but the percentage of BCUs in 4FGL is reduced to 5.1\%. The $\gamma$-ray photon index, synchrotron peak frequency, and high energy peak frequency of a large sample are used to investigate the relationship between FSRQs and BL Lacs (LBLs, IBLs, and HBLs).Comment: Accepted for publication in MNRA

Elliptic flow in proton-proton collisions at 7 TeV

The angular correlations measured in proton-proton collisions at 7 TeV are decomposed into contributions from back to back emission and elliptic flow. Modeling the dominant term in the correlation functions as a momentum conservation effect or as an effect of the initial transverse velocity of the source, the remaining elliptic flow component can be estimated. The elliptic flow coefficient extracted from the CMS Collaboration data is 0.04-0.08. No additional small-angle, ridge-like correlations are needed to explain the experimental data

On the Theory of Relativistic Strong Plasma Waves

The influence of motion of ions and electron temperature on nonlinear one-dimensional plasma waves with velocity close to the speed of light in vacuum is investigated. It is shown that although the wavebreaking field weakly depends on mass of ions, the nonlinear relativistic wavelength essentially changes. The nonlinearity leads to the increase of the strong plasma wavelength, while the motion of ions leads to the decrease of the wavelength. Both hydrodynamic approach and kinetic one, based on Vlasov-Poisson equations, are used to investigate the relativistic strong plasma waves in a warm plasma. The existence of relativistic solitons in a thermal plasma is predicted.Comment: 13 pages, 8 figure

First Limits on Left-Right Symmetry Scale from LHC Data

We use the early Large Hadron Collider data to set the lower limit on the scale of Left-Right symmetry, by searching for the right-handed charged gauge boson $W_R$ via the final state with two leptons and two jets, for 33/pb integrated luminosity and 7 TeV center-of-mass energy. In the absence of a signal beyond the Standard Model background, we set the bound M_WR > 1.4 TeV at 95% C.L.. This result is obtained for a range of right-handed neutrino masses of the order of few 100 GeV, assuming no accidental cancelation in right-handed lepton mixings.Comment: 4 pages, added reference

Excitation of nonlinear two-dimensional wake waves in radially-nonuniform plasma

It is shown that an undesirable curvature of the wave front of two-dimensional nonlinear wake wave excited in uniform plasma by a relativistic charged bunch or laser pulse may be compensated by radial change of the equilibrium plasma density.Comment: 6 pages, 4 figure