## Search

Now showing items 1-10 of 68

JavaScript is disabled for your browser. Some features of this site may not work without it.

All of UA Campus RepositoryCommunitiesTitleAuthorsIssue DateSubmit DateSubjectsPublisherJournalThis CollectionTitleAuthorsIssue DateSubmit DateSubjectsPublisherJournal

Journal

PHYSICAL REVIEW D (68)

AuthorsUniv Arizona, Dept Phys (51)Abbott, B. (11)Cheu, E. (11)Aaboud, M. (9)Aad, G. (9)Acharya, B. S. (9)Paschalidis, Vasileios (9)Amidei, D. (8)Annovi, A. (8)Nayyar, R. (8)View MoreTypesArticle (68)
AboutUA Faculty PublicationsUA DissertationsUA Master's ThesesUA Honors ThesesUA PressUA YearbooksUA Catalogs

Now showing items 1-10 of 68

- List view
- Grid view
- Sort Options:
- Relevance
- Title Asc
- Title Desc
- Issue Date Asc
- Issue Date Desc
- Results Per Page:
- 5
- 10
- 20
- 40
- 60
- 80
- 100

Dark Energy Survey year 1 results: Cosmological constraints from galaxy clustering and weak lensing

Abbott, T. M. C.; Abdalla, F. B.; Alarcon, A.; Aleksić, J.; Allam, S.; Allen, S.; Amara, A.; Annis, J.; Asorey, J.; Avila, S.; et al. (AMER PHYSICAL SOC, 2018-08-27)

We present cosmological results from a combined analysis of galaxy clustering and weak gravitational lensing, using 1321 deg(2) of griz imaging data from the first year of the Dark Energy Survey (DES Y1). We combine three two-point functions: (i) the cosmic shear correlation function of 26 million source galaxies in four redshift bins, (ii) the galaxy angular autocorrelation function of 650,000 luminous red galaxies in five redshift bins, and (iii) the galaxy-shear cross-correlation of luminous red galaxy positions and source galaxy shears. To demonstrate the robustness of these results, we use independent pairs of galaxy shape, photometric-redshift estimation and validation, and likelihood analysis pipelines. To prevent confirmation bias, the bulk of the analysis was carried out while "blind" to the true results; we describe an extensive suite of systematics checks performed and passed during this blinded phase. The data are modeled in flat Lambda CDM and wCDM cosmologies, marginalizing over 20 nuisance parameters, varying 6 (for Lambda CDM) or 7 (for wCDM) cosmological parameters including the neutrino mass density and including the 457 x 457 element analytic covariance matrix. We find consistent cosmological results from these three two-point functions and from their combination obtain S-8 equivalent to sigma(8) (Omega(m)/0.3)(0.5) = 0.773(-0.020)(+0.026) and Omega(m) = 0.267(-0.017)(+0.030) for Lambda CDM; for wCDM, we find S-8 = 0.782(-0.024)(+0.036) , Omega(m) = 0.284(-0.030)(+0.033), and w = -0.82(-0.20)(+0.21) at 68% C.L. The precision of these DES Y1 constraints rivals that from the Planck cosmic microwave background measurements, allowing a comparison of structure in the very early and late Universe on equal terms. Although the DES Y1 best-fit values for S-8 and Omega(m) are lower than the central values from Planck for both Lambda CDM and wCDM, the Bayes factor indicates that the DES Y1 and Planck data sets are consistent with each other in the context of Lambda CDM. Combining DES Y1 with Planck, baryonic acoustic oscillation measurements from SDSS, 6dF, and BOSS and type Ia supernovae from the Joint Lightcurve Analysis data set, we derive very tight constraints on cosmological parameters: S-8 = 0.802 +/- 0.012 and Omega(m) = 0.298 +/- 0.007 in Lambda CDM and w = -1.00(-0.04)(+0.05) in wCDM. Upcoming Dark Energy Survey analyses will provide more stringent tests of the Lambda CDM model and extensions such as a time-varying equation of state of dark energy or modified gravity.

Density split statistics: Joint model of counts and lensing in cells

Friedrich, O.; Gruen, D.; DeRose, J.; Kirk, D.; Krause, E.; McClintock, T.; Rykoff, E. S.; Seitz, S.; Wechsler, R. H.; Bernstein, G. M.; et al. (AMER PHYSICAL SOC, 2018-07-13)

We present density split statistics, a framework that studies lensing and counts-in-cells as a function of foreground galaxy density, thereby providing a large-scale measurement of both 2-point and 3-point statistics. Our method extends our earlier work on trough lensing and is summarized as follows: given a foreground (low redshift) population of galaxies, we divide the sky into subareas of equal size but distinct galaxy density. We then measure lensing around uniformly spaced points separately in each of these subareas, as well as counts-in-cells statistics (CiC). The lensing signals trace the matter density contrast around regions of fixed galaxy density. Through the CiC measurements this can be related to the density profile around regions of fixed matter density. Together, these measurements constitute a powerful probe of cosmology, the skewness of the density field and the connection of galaxies and matter. In this paper we show how to model both the density split lensing signal and CiC from basic ingredients: a non-linear power spectrum, clustering hierarchy coefficients from perturbation theory and a parametric model for galaxy bias and shot-noise. Using N-body simulations, we demonstrate that this model is sufficiently accurate for a cosmological analysis on year 1 data from the Dark Energy Survey.

Effects of spin on magnetized binary neutron star mergers and jet launching

Ruiz, Milton; Tsokaros, Antonios; Paschalidis, Vasileios; Shapiro, Stuart L. (AMER PHYSICAL SOC, 2019-04-17)

Events GW170817 and GRB 170817A provide the best confirmation so far that compact binary mergers where at least one of the companions is a neutron star can be the progenitors of short gamma-ray bursts (sGRBs). An open question for GW170817 remains the values and impact of the initial neutron star spins. The initial spins could possibly affect the remnant black hole mass and spin, the remnant disk, and the formation and lifetime of a jet and its outgoing electromagnetic Poynting luminosity. Here we summarize our general relativistic magnetohydrodynamic simulations of spinning, neutron star binaries undergoing merger, and delayed collapse to a black hole. The binaries consist of two identical stars, modeled as Gamma = 2 polytropes, in quasicircular orbit, each with spins chi(Ns) = -0.053, 0, 0.24, or 0.36. The stars arc endowed initially with a dipolar magnetic field extending from the interior into the exterior, as in a radio pulsar. Following the merger, the redistribution of angular momentum by magnetic braking and magnetic turbulent viscosity in the hypermassive neutron star (HMNS) remnant, along with the loss of angular momentum due to gravitational radiation, induces the formation of a massive, nearly uniformly rotating inner core surrounded by a magnetized Keplerian disklike envelope. The HMNS eventually collapses to a black hole, with spin a/M-BH similar or equal to 0.78 independent of the initial spin of the neutron stars, surrounded by a magnetized accretion disk. The larger the initial neutron star spin the heavier the disk. After Delta t similar to 3000M - 4000M similar to 45(M-Ns /1.625 M-circle dot) ms - 60(M-Ns /1.625 M-circle dot) ms following merger, a mildly relativistic jet is launched. The lifetime of the jet [Delta t similar to 100(M-Ns 11.625 M-circle dot) ms - 140(M-Ns /1.625 M-circle dot) ms] and its outgoing Poynting luminosity [L-Em similar to 10(51.5 +/- 1)erg /s] are consistent with typical sGRBs, as well as with the Blandford-Znajek mechanism for launching jets and their associated Poynting luminosities.

Search for flavor-changing neutral currents in top quark decays t -> Hc and t -> Hu in multilepton final states in proton-proton collisions at root s=13 TeV with the ATLAS detector

Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Abidi, S. H.; AbouZeid, O. S.; Abraham, N. L.; Abramowicz, H.; et al. (AMER PHYSICAL SOC, 2018-08-06)

Flavor-changing neutral currents are not present in the Standard Model at tree level and are suppressed in loop processes by the unitarity of the Cabibbo-Kobayashi-Maskawa matrix; the corresponding rates for top quark decay processes are experimentally unobservable. Extensions of the Standard Model can generate new flavor-changing neutral current processes, leading to signals which, if observed, would be unambiguous evidence of new interactions. A data set conesponding to an integrated luminosity of 36.1 fb(-1) of pp collisions at a center-of-mass energy of root s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider is used to search for top quarks decaying to up or charm quarks with the emission of a Higgs boson, with subsequent Higgs boson decay to final states with at least one electron or muon. No signal is observed and limits on the branching fractions B(t -> Hc) < 0.16% and B(t -> Hu) < 0.19% at 95% confidence level are obtained (with expected limits of 0.15% in both cases).

Vacuum stabilized by anomalous magnetic moment

Evans, Stefan; Rafelski, Johann (AMER PHYSICAL SOC, 2018-07-10)

An analytical result for Euler-Heisenberg effective action, valid for electron spin g-factor vertical bar g vertical bar < 2, was extended to the domain vertical bar g vertical bar > 2 via discovered periodicity of the effective action. This allows for a simplified computation of vacuum instability modified by the electron's measured g = 2.002319. We find a strong suppression of vacuum decay into electron positron pairs when magnetic fields are dominant. The result is reminiscent of mass catalysis by magnetic fields.

Cosmological constraints on unstable particles: Numerical bounds and analytic approximations

Dienes, Keith R.; Kumar, Jason; Stengel, Patrick; Thomas, Brooks (AMER PHYSICAL SOC, 2019-02-12)

Many extensions of the Standard Model predict large numbers of additional unstable particles whose decays in the early universe are tightly constrained by observational data. For example, the decays of such particles can alter the ratios of light-element abundances, give rise to distortions in the cosmic microwave background, alter the ionization history of the Universe, and contribute to the diffuse photon flux. Constraints on new physics from such considerations are typically derived for a single unstable particle species with a single well-defined mass and characteristic lifetime. In this paper, by contrast, we investigate the cosmological constraints on theories involving entire ensembles of decaying particles-ensembles which span potentially broad ranges of masses and lifetimes. In addition to providing a detailed numerical analysis of these constraints, we also formulate a set of simple analytic approximations for these constraints which may be applied to generic ensembles of unstable particles which decay into electromagnetically interacting final states. We then illustrate how these analytic approximations can be used to constrain a variety of toy scenarios for physics beyond the Standard Model. For ease of reference, we also compile our results in the form of a table which can be consulted independently of the rest of the paper. It is thus our hope that this work might serve as a useful reference for future model-builders concerned with cosmological constraints on decaying particles, regardless of the particular model under study.

Search for supersymmetry in events with four or more leptons in root s=13 TeV pp collisions with ATLAS

Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abidi, S. H.; AbouZeid, O. S.; Abraham, N. L.; Abramowicz, H.; Abreu, H.; et al. (AMER PHYSICAL SOC, 2018-08-15)

Results from a search for supersymmetry in events with four or more charged leptons (electrons, muons and taus) are presented. The analysis uses a data sample corresponding to 36.1 fb(-1) of proton-proton collisions delivered by the Large Hadron Collider at root s = 13 TeV and recorded by the ATLAS detector. Four-lepton signal regions with up to two hadronically decaying taus are designed to target a range of supersymmetric scenarios that can be either enriched in or depleted of events involving the production and decay of a Z boson. Data yields are consistent with Standard Model expectations and results are used to set upper limits on the event yields from processes beyond the Standard Model. Exclusion limits are set at the 95% confidence level in simplified models of general gauge mediated supersymmetry, where Higgsino masses are excluded up to 295 GeV. In R-parity-violating simplified models with decays of the lightest supersymmetric particle to charged leptons, lower limits of 1.46, 1.06, and 2.25 TeV are placed on wino, slepton and gluino masses, respectively.

Search for heavy charged long-lived particles in the ATLAS detector in 36.1 fb(-1) of proton-proton collision data at root s=13 Te V

Berlendis, S.; Cheu, E.; Delitzsch, C.M.; Johns, K.A.; Jones, S.; Lampl, W.; LeBlanc, M.; Leone, R.; Loch, P.; Nayyar, R.; et al. (AMER PHYSICAL SOC, 2019-05-28)

A search for heavy charged long-lived particles is performed using a data sample of 36.1 fb(-1) of protonproton collisions at root s = 13 TeV collected by the ATLAS experiment at the Large Hadron Collider. The search is based on observables related to ionization energy loss and time of flight, which are sensitive to the velocity of heavy charged particles traveling significantly slower than the speed of light. Multiple search strategies for a wide range of lifetimes, corresponding to path lengths of a few meters, are defined as model independently as possible, by referencing several representative physics cases that yield long-lived particles within supersymmetric models, such as gluinos/squarks (R-hadrons), charginos and staus. No significant deviations from the expected Standard Model background are observed. Upper limits at 95% confidence level are provided on the production cross sections of long-lived R-hadrons as well as directly pair-produced staus and charginos. These results translate into lower limits on the masses of long-lived gluino, sbottom and stop R-hadrons, as well as staus and charginos of 2000, 1250, 1340, 430, and 1090 GeV, respectively.

Frequency-domain waveform approximants capturing Doppler shifts

Chamberlain, Katie; Moore, Christopher J.; Gerosa, Davide; Yunes, Nicolás (AMER PHYSICAL SOC, 2019-01-15)

Gravitational-wave astrophysics has only just begun, and as current detectors are upgraded and new detectors are built, many new, albeit faint, features in the signals will become accessible. One such feature is the presence of time-dependent Doppler shifts, generated by the acceleration of the center of mass of the gravitational-wave emitting system. We here develop a generic method that takes a frequency-domain, gravitational-wave model devoid of Doppler shifts and introduces modifications that incorporate them. Building upon a perturbative expansion that assumes the Doppler-shift velocity is small relative to the speed of light, the method consists of the inclusion of a single term in the Fourier phase and two terms in the Fourier amplitude. We validate the method through matches between waveforms with a Doppler shift in the time domain and waveforms constructed with our method for two toy problems: constant accelerations induced by a distant third body and Gaussian accelerations that resemble a kick profile. We find mismatches below similar to 10(-6) for all of the astrophysically relevant cases considered and that improve further at smaller velocities. The work presented here will allow for the use of future detectors to extract new, faint features in the signal from the noise.

Lattice computation of the electromagnetic contributions to kaon and pion masses

Basak, S.; Bazavov, A.; Bernard, C.; DeTar, C.; Levkova, L.; Freeland, E.; Gottlieb, Steven; Torok, A.; Heller, U. M.; Laiho, J.; et al. (AMER PHYSICAL SOC, 2019-02-15)

We present a lattice calculation of the electromagnetic (EM) effects on the masses of light pseudoscalar mesons. The simulations employ 2 + 1 dynamical flavors of asqtad QCD quarks and quenched photons. Lattice spacings vary from approximate to 0.12 fm to approximate to 0.045 fm. We compute the quantity epsilon, which parametrizes the corrections to Dashen's theorem for the K+-K-0 EM mass splitting, as well as epsilon(K0), which parametrizes the EM contribution to the mass of the K-0 itself. An extension of the nonperturbative EM renormalization scheme introduced by the BMW group is used in separating EM effects from isospin-violating quark mass effects. We correct for leading finite-volume effects in our realization of lattice electrodynamics in chiral perturbation theory, and remaining finite-volume errors are relatively small. While electroquenched effects are under control for epsilon, they are estimated only qualitatively for epsilon(K0) and constitute one of the largest sources of uncertainty for that quantity. We find epsilon = 0.78(1)(stat)((+8)(-11))(syst) and epsilon(K0) = 0.035(3)(stat)(20)(syst). We then use these results on 2 + 1 + 1 flavor pure QCD highly improved staggered quark (HISQ) ensembles and find m(u)/m(d) = 0.4529(48)(stat)((+150)(-67))(syst).

The export option will allow you to export the current search results of the entered query to a file. Different formats are available for download. To export the items, click on the button corresponding with the preferred download format.

By default, clicking on the export buttons will result in a download of the allowed maximum amount of items.

To select a subset of the search results, click "Selective Export" button and make a selection of the items you want to export. The amount of items that can be exported at once is similarly restricted as the full export.

After making a selection, click one of the export format buttons. The amount of items that will be exported is indicated in the bubble next to export format.