18244927
Nuclear Shadowing and Antishadowing in a Unitarized BFKL Equation
The nuclear shadowing and antishadowing effects are explained by a unitarized BFKL equation. The Q2and x-variations of the nuclear parton distributions are detailed based on the level of the unintegrated gluon distribution. In particular, the asymptotical behavior of the unintegrated gluon distribution near the saturation limit in nuclear targets is studied. Our results in the nuclear targets are insensitive to the input distributions if the parameters are fixed by the data of a free proton. PACS numbers: 13.60.Hb; 12.38.Bx. keywords: nuclear shadowing and antishadowing; unintegrated gluon distribution in nuclei; QCD evolution equation Supported by National Natural Science Foundation of China 10135060, 10475028 and 10205004. Corresponding author, E-mail: weizhu @mail.ecnu.edu.cn
12305729
Can a chaotic solution in the QCD evolution equation restrain high-energy collider physics?
We indicate that the random aperiodic oscillation of the gluon distributions in a modified Balisky–Fadin–Kuraev–Lipatov (BFKL) equation has positive Lyapunov exponents. This first example of chaos in QCD evolution equations, raises the sudden disappearance of the gluon distributions at a critical small value of the Bjorken variable x and may stop the increase of the new particle events in an ultra high energy hadron collider. PACS numbers: 12.38.Bx, 24.85.+p keywords: QCD evolution equation; Chaos The gluon distributions are important knowledge in research of high energy collider physics. The gluon distributions of the nucleon cannot be extracted directly from the measured structure functions in deep inelastic scattering experiments and they are mainly predicted by using the QCD evolution equations. However, the linear Dokshitzer-GribovLipatov-Altarelli-Parisi (DGLAP) and Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution equations are no longer reliable at ultra higher energy, therefore a series nonlinear evolution equations, for example, the GLR-MQ-ZRS Gribov-Levin-Ryskin, Mueller-Qiu, Zhu-Ruan-Shen (GLR-MQ-ZRS) and Balitsky-Kovchegov (BK) equations were proposed, in which the corrections of the gluon fusion are considered. An important prediction of these equations is that the gluon distributions approach to a so-called ‘saturation limit’ asymptotically at small Bjorken variable x, where gluon splitting is balanced with fusion. As we well know, the nonlinear dynamics may have a characteristic solution–chaos, which have been observed in many natural phenomena. Therefore, it is interesting to ask: Does nonlinear QCD evolution equation of gluon distribution also have chaotic solution? How does it impact the gluon distribution? Recently, we have proposed a nonlinear modified BFKL (MD-BFKL) equation in Ref. [9], which describes the corrections of the gluon recombination to the BFKL equation. We found that the unintegrated gluon distribution function F (x, k) in the MD-BFKL equation in the fixed coupling approximation begins its smooth evolution under suppression of the gluon fusion likes the solution of the BK equation, but when x comes to a smaller critical xc, F (x, k ) will oscillate aperiodically near the evolution endpoint k 0. This behavior has the characteristic feature of chaos: random and sensitive to the initial conditions. Furthermore, with the enhancement of oscillation, the distribution F (x, k) will disappear suddenly at xc. This kind of phase transition led by chaotic solutions will certainly call our attention to reconsider the future of high energy collider physics carefully. In this letter, we indicate that the above-mentioned oscillate solution in the MD-BFKL equation is really chaos and it still holds in the running coupling case.
14042487
Prediction for unintegrated parton distributions
Unintegrated parton distributions in the proton and nucleus are predicted by a modified Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) equation incorporating the shadowing corrections, which include exact energy-momentum conservation in each splitting and fusion vertices. We find that the nuclear shadowing effects are obvious, although they are far from the saturation limit. On the other hand, we point out that the suppression of the unintegrated gluon distribution toward lower k{sub t}{sup 2} may arise from the valence-like input rather than the saturation effects.
121492263
Antishadowing properties in the small-x region
Abstract The properties of the modified Gribov-Levin-Ryskin evolution equation which incorporates both shadowing and antishadowing are analyzed. We find that some important conclusions of the GLR equation should be rewritten.
124870414
Antishadowing Corrections in the Evolution Equation of Quark Distributions
We introduce the antishadowing effect to restore the momentum sum rule in the quantum chromodynamics evolution equation for quarks in small x region.
122554827
Antishadowing contribution to the small x behavior of the gluon distribution
Abstract We introduce antishadowing into the Gribov-Levin-Ryskin evolution equation and restore the momentum sum rule. It is found clearly that antishadowing will modify the shadowing effect in the region 10 −4 x −2 when a hot spot with small radius exists in the nucleon.
119226266
Cold stream stability during minor mergers
We use high-resolution Eulerian simulations to study the stability of cold gas flows in a galaxy size dark matter halo (10(12) M-circle dot) at redshift z = 2. Our simulations show that a cold stream penetrating a hot gaseous halo is stable against thermal convection and Kelvin-Helmholtz instability. We then investigate the effect of a satellite orbiting the main halo in the plane of the stream. The satellite is able to perturb the stream and to inhibit cold gas accretion towards the centre of the halo for 0.5 Gyr. However, if the supply of cold gas at large distances is kept constant, the cold stream is able to re-establish itself after 0.3 Gyr. We conclude that cold streams are very stable against a large variety of internal and external perturbations.
36824022
peace: pulsar evaluation algorithm for candidate extraction – a software package for post-analysis processing of pulsar survey candidates
Modern radio pulsar surveys produce a large volume of prospective candidates, the majority of which are polluted by human-created radio frequency interference or other forms of noise. Typically, large numbers of candidates need to be visually inspected in order to determine if they are real pulsars. This process can be labour intensive. In this paper, we introduce an algorithm called Pulsar Evaluation Algorithm for Candidate Extraction (PEACE) which improves the efficiency of identifying pulsar signals. The algorithm ranks the candidates based on a score function. Unlike popular machine-learning-based algorithms, no prior training data sets are required. This algorithm has been applied to data from several large-scale radio pulsar surveys. Using the human-based ranking results generated by students in the Arecibo Remote Command Center programme, the statistical performance of PEACE was evaluated. It was found that PEACE ranked 68 per cent of the student-identified pulsars within the top 0.17 per cent of sorted candidates, 95 per cent within the top 0.34 per cent and 100 per cent within the top 3.7 per cent. This clearly demonstrates that PEACE significantly increases the
118616891
X-RAY OBSERVATIONS OF HIGH-B RADIO PULSARS
The study of high-magnetic-field pulsars is important for examining the relationships between radio pulsars, magnetars, and X-ray-isolated neutron stars (XINSs). Here, we report on X-ray observations of three such high-magnetic-field radio pulsars. We first present the results of a deep XMM-Newton observation of PSR J1734–3333, taken to follow up on its initial detection in 2009. The pulsar's spectrum is well fit by a blackbody with a temperature of 300 ± 60 eV, with bolometric luminosity for a distance of 6.1 kpc. We detect no X-ray pulsations from the source, setting a 1σ upper limit on the pulsed fraction of 60% in the 0.5-3 keV band. We compare PSR J1734–3333 to other rotation-powered pulsars of similar age and find that it is significantly hotter, supporting the hypothesis that the magnetic field affects the observed thermal properties of pulsars. We also report on XMM-Newton and Chandra observations of PSRs B1845–19 and J1001–5939. We do not detect either pulsar, setting 3σ upper limits on their blackbody temperatures of 48 and 56 eV, respectively. Despite the similarities in rotational properties, these sources are significantly cooler than all but one of the XINSs, which we attribute to the two groups having been born with different magnetic fields and hence evolving differently.
55413960
SEARCHING FOR PULSARS USING IMAGE PATTERN RECOGNITION
In the modern era of big data, many fields of astronomy are generating huge volumes of data, the analysis of which can sometimes be the limiting factor in research. Fortunately, computer scientists have developed powerful data-mining techniques that can be applied to various fields. In this paper, we present a novel artificial intelligence (AI) program that identifies pulsars from recent surveys by using image pattern recognition with deep neural nets—the PICS (Pulsar Image-based Classification System) AI. The AI mimics human experts and distinguishes pulsars from noise and interference by looking for patterns from candidate plots. Different from other pulsar selection programs that search for expected patterns, the PICS AI is taught the salient features of different pulsars from a set of human-labeled candidates through machine learning. The training candidates are collected from the Pulsar Arecibo L-band Feed Array (PALFA) survey. The information from each pulsar candidate is synthesized in four diagnostic plots, which consist of image data with up to thousands of pixels. The AI takes these data from each candidate as its input and uses thousands of such candidates to train its ~9000 neurons. The deep neural networks in this AI system grant it superior ability to recognize various types of pulsars as well as their harmonic signals. The trained AI's performance has been validated with a large set of candidates from a different pulsar survey, the Green Bank North Celestial Cap survey. In this completely independent test, the PICS ranked 264 out of 277 pulsar-related candidates, including all 56 previously known pulsars and 208 of their harmonics, in the top 961 (1%) of 90,008 test candidates, missing only 13 harmonics. The first non-pulsar candidate appears at rank 187, following 45 pulsars and 141 harmonics. In other words, 100% of the pulsars were ranked in the top 1% of all candidates, while 80% were ranked higher than any noise or interference. The performance of this system can be improved over time as more training data are accumulated. This AI system has been integrated into the PALFA survey pipeline and has discovered six new pulsars to date.
7392737
Timing of a Young Mildly Recycled Pulsar with a Massive White Dwarf Companion
We report on timing observations of the recently discovered binary pulsar PSR J1952+2630 using the Arecibo Observatory. The mildly recycled 20.7-ms pulsar is in a 9.4-hr orbit with a massive, MW D > 0.93 M⊙, white dwarf (WD) companion. We present, for the first time, a phase-coherent timing solution, with precise spin, astrometric, and Keplerian orbital parameters. This shows that the characteristic age of PSR J1952+2630 is 77 Myr, younger by one order of magnitude than any other recycled pulsar–massive WD system. We derive an upper limit on the true age of the system of 150 Myr. We investigate the formation of PSR J1952+2630 using detailed modelling of the mass-transfer process from a naked helium star on to the neutron star following a common-envelope phase (Case BB Roche-lobe overflow). From our modelling of the progenitor system, we constrain the accretion efficiency of the neutron star, which suggests a value between 100 and 300% of the Eddington accretion limit. We present numerical models of the chemical structure of a possible oxygenneon-magnesium WD companion. Furthermore, we calculate the past and the future spin evolution of PSR J1952+2630, until the system merges in about 3.4 Gyr due to gravitational wave emission. Although we detect no relativistic effects in our timing analysis we show that several such effects will become measurable with continued observations over the next 10 years; thus PSR J1952+2630 has potential as a testbed for gravitational theories.