118618637
The Dependence of Subhalo Abundance on Halo Concentration
Hierarchical structure formation implies that the number of subhalos within a dark matter halo depends not only on halo mass, but also on the formation history of the halo. This dependence on the formation history, which is highly correlated with halo concentration, can account for the super-Poissonian scatter in subhalo occupation at a fixed halo mass that has been previously measured in simulations. Here we propose a model to predict the subhalo abundance function for individual host halos that incorporates both halo mass and concentration. We combine results of cosmological simulations with a new suite of zoom-in simulations of Milky Way-mass halos to calibrate our model. We show that the model can successfully reproduce the mean and the scatter of subhalo occupation in these simulations. The implications of this correlation between subhalo abundance and halo concentration are further investigated. We also discuss cases in which inferences about halo properties can be affected if this correlation between subhalo abundance and halo concentration is ignored; in these cases, our model would give a more accurate inference. We propose that with future deep surveys, satellite occupation in the low-mass regime can be used to verify the existence of halo assembly bias.
119269420
Topological susceptibility to the one-loop order in chiral perturbation theory
We derive the topological susceptibility to the one-loop order in the chiral effective theory of QCD, for an arbitrary number of flavors.
118080950
GPU-Based Conjugate Gradient Solver for Lattice QCD with Domain-Wall Fermions
We present the first GPU-based conjugate gradient (CG) solver for lattice QCD with domain-wall fermions (DWF). It is well-known that CG is the most time-consuming part in the Hybrid Monte Carlo simulation of unquenched lattice QCD, which becomes even more computational demanding for lattice QCD with exact chiral symmetry. We have designed a CG solver for the general 5-dimensional DWF operator on NVIDIA CUDA architecture with mixed-precision, using the defect correction as well as the reliable updates algorithms. We optimize our computation by even-odd preconditioning in the 4D space-time lattice, plus several innovative techniques for CUDA kernels. For NVIDIA GeForce GTX 285/480, our CG solver attains 180/233 Gflops (sustained).
119304335
RHAPSODY. II. SUBHALO PROPERTIES AND THE IMPACT OF TIDAL STRIPPING FROM A STATISTICAL SAMPLE OF CLUSTER-SIZE HALOS
We discuss the properties of subhalos in cluster-size halos, using a high-resolution statistical sample: the RHAPSODY simulations introduced in Wu et al. We demonstrate that the criteria applied to select subhalos have significant impact on the inferred properties of the sample, including the scatter in the number of subhalos, the correlation between the subhalo number and formation time, and the shape of subhalos' spatial distribution and velocity structure. We find that the number of subhalos, when selected using the peak maximum circular velocity in their histories (a property expected to be closely related to the galaxy luminosity), is uncorrelated with the formation time of the main halo. This is in contrast to the previously reported correlation from studies where subhalos are selected by the current maximum circular velocity; we show that this difference is a result of the tidal stripping of the subhalos. We also find that the dominance of the main halo and the subhalo mass fraction are strongly correlated with halo concentration and formation history. These correlations are important to take into account when interpreting results from cluster samples selected with different criteria. Our sample also includes a fossil cluster, which is presented separately and placed in the context of the rest of the sample.
62834395
SUSSING MERGER TREES: the influence of the halo finder
Merger tree codes are routinely used to follow the growth and merger of dark matter haloes in simulations of cosmic structure formation. Whereas in Srisawat et. al. we compared the trees built using a wide variety of such codes, here we study the influence of the underlying halo catalogue upon the resulting trees. We observe that the specifics of halo finding itself greatly influences the constructed merger trees. We find that the choices made to define the halo mass are of prime importance. For instance, amongst many potential options different finders select self-bound objects or spherical regions of defined overdensity, decide whether or not to include substructures within the mass returned and vary in their initial particle selection. The impact of these decisions is seen in tree length (the period of time a particularly halo can be traced back through the simulation), branching ratio (essentially the merger rate of subhaloes) and mass evolution. We therefore conclude that the choice of the underlying halo finder is more relevant to the process of building merger trees than the tree builder itself. We also report on some built-in features of specific merger tree codes that (sometimes) help to improve the quality of the merger trees produced.
119242151
Topological susceptibility in two flavors lattice QCD with the optimal domain-wall fermion
Abstract We determine the topological susceptibility of the gauge configurations generated by lattice simulations using two flavors of optimal domain-wall fermion on the 16 3 × 32 lattice with length 16 in the fifth dimension, at the lattice spacing a ≃ 0.1 fm . Using the adaptive thick-restart Lanczos algorithm, we project the low-lying eigenmodes of the overlap Dirac operator, and obtain the topological charge of each configuration, for eight ensembles with pion masses in the range 220–550 MeV. From the topological charge, we compute the topological susceptibility and the second normalized cumulant. Our result of the topological susceptibility agrees with the sea-quark mass dependence predicted by the chiral perturbation theory and provides a determination of the chiral condensate, Σ MS ¯ ( 2 GeV ) = [ 259 ( 6 ) ( 7 ) MeV ] 3 , and the pion decay constant F π = 92 ( 12 ) ( 2 ) MeV .
202135211
Evidence of b-Jet Quenching in PbPb Collisions at $\sqrt{s_{NN}}=2.76$ TeV
122411213
Potential physics measurement with ALICE electromagnetic calorimeters
Abstract We present the two electromagnetic calorimeters of the ALICE (A Large Ion Collider Experiment) experiment at LHC (Large Hadron Collider). One is the high-resolution PHOton Spectrometer (PHOS) made of lead tungsten crystals and the other is the ElectroMagnetic Calorimeter (EMCal), a Lead-Scintillator sampling calorimeter. They are dedicated to the measurement and identification of direct photons, light neutral mesons such as π 0 , η and ω ( 782 ) , and jets emitted in proton-proton and heavy-ion collisions at the LHC energies. The PHOS is capable of precisely detecting photons with momentum range between 0.1 GeV/c and 100 GeV/c and the EMCal can extend the prompt photon and light neutral meson momentum measurement beyond 200 GeV/c. The objective of the study is to explore the physics of strongly interacting QCD matter under extreme conditions of energy density.
121353892
Measurements of jet shape in 2.76 TeV PbPb collisions with CMS
Abstract The fragmentation properties of inclusive jets produced in PbPb collisions at a center of mass energy of s N N = 2.76 TeV are characterized by measuring differential jet shapes. The jet shape is defined as the fractional jet transverse momentum carried by charged particles emitted at a distance r from the jet axis, with jets reconstructed using the anti- k T clustering algorithm. The jet shapes are measured for reconstructed jet p T , jet > 100 GeV / c and charged hardons with p T > 1 GeV / c . Different background subtraction methods are employed to remove the contribution from the underlying events. The results obtained for PbPb collisions as a function of collision centrality are compared to reference distributions from pp data collected at the same collision energy. For the most central collisions, the jet shapes are found to be modified at large distance from the jet axis.
12396289
Two particle correlations: A probe of the LHC QCD medium
The properties of γ-jet pairs emitted in heavy-ion collisions provide an accurate mean to perform a tomographic measurement of the medium created in the collision through the study of the medium modified jet properties. The idea is to measure the distribution of hadrons emitted on the opposite side of the direct photon. The feasibility of such measurements is studied by applying the approach on the simulation data, we have demonstrated that this method allows us to measure, with a good approximation, both the jet fragmentation and the back-to-back azimuthal alignment of the direct photon and the jet. Comparing these two observables measured in pp collisions with the ones measured in AA collisions reveals the modifications induced by the medium on the jet structure and consequently allows us to infer the medium properties. In this contribution, we discuss a first attempt of such measurements applied to real proton-proton data from the ALICE experiment.
122184484
CHARM QUARK ENERGY LOSS IN DENSE MATTER WITHIN THE LIGHT-CONE PATH INTEGRAL APPROACH
The energy loss of heavy quarks traversing color dense matter is calculated with an analytical formula derived within the light-cone path integral (LCPI) approach. We find that the energy loss mechanism is dominated by gluon radiation and induces a suppression pattern of charm quark different from the suppression of light quarks. We find also that this radiative energy-loss is proportional to L2 for energetic quarks, but changes to a L dependance with decreasing quark energy, where L is the length of the traversed medium.