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PHYSICAL REVIEW D (65)

AuthorsUniv Arizona, Dept Phys (49)Abbott, B. (11)Cheu, E. (11)Aaboud, M. (9)Aad, G. (9)Acharya, B. S. (9)Amidei, D. (8)Annovi, A. (8)Nayyar, R. (8)Paschalidis, Vasileios (8)View MoreTypesArticle (65)
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Search for heavy resonances decaying to a photon and a hadronically decaying Z/W/H boson in pp collisions at root s=13 TeV with the ATLAS detector

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, 2018-08-28)

Many extensions of the Standard Model predict new resonances decaying to a Z, W, or Higgs boson and a photon. This paper presents a search for such resonances produced in pp collisions at root s = 13 TeV using a data set with an integrated luminosity of 36.1 fb(-1) collected by the ATLAS detector at the LHC. The Z/W/H bosons are identified through their decays to hadrons. The data are found to be consistent with the Standard Model expectation in the entire investigated mass range. Upper limits are set on the production cross section times branching fraction for resonance decays to Z.W + gamma in the mass range from 1.0 to 6.8 TeV and for the first time into H + gamma in the mass range from 1.0 to 3.0 TeV.

GUT precursors and entwined SUSY: The phenomenology of stable nonsupersymmetric strings

Abel, Steven; Dienes, Keith R.; Mavroudi, Eirini (AMER PHYSICAL SOC, 2018-06-25)

Recent work has established a method of constructing nonsupersymmetric string models that are stable, with near-vanishing one-loop dilaton tadpoles and cosmological constants. This opens up the tantalizing possibility of realizing stable string models whose low-energy limits directly resemble the Standard Model rather than one of its supersymmetric extensions. In this paper we consider the general structure of such strings and find that they share two important phenomenological properties. The first is a so-called "GUT-precursor" structure in which new GUT-like states appear with masses that can be many orders of magnitude lighter than the scale of gauge coupling unification. These states allow a parametrically large compactification volume, even in weakly coupled heterotic strings, and in certain regions of parameter space can give rise to dramatic collider signatures which serve as "smoking guns" for this overall string framework. The second is a residual "entwined-SUSY" (or e-SUSY) structure for the matter multiplets in which different multiplet components carry different horizontal U(1) charges. As a concrete example and existence proof of these features, we present a heterotic string model that contains the fundamental building blocks of the Standard Model such as the Standard-Model gauge group, complete chiral generations, and Higgs fields-all without supersymmetry. Even though massless gravitinos and gauginos are absent from the spectrum, we confirm that this model has an exponentially suppressed one-loop dilaton tadpole and displays both the GUT-precursor and e-SUSY structures. We also discuss some general phenomenological properties of e-SUSY, such as cancellations in radiative corrections to scalar masses, the possible existence of a corresponding approximate moduli space, and the prevention of rapid proton decay.

Future prospects of mass-degenerate Higgs bosons in the CP-conserving two-Higgs-doublet model

Bian, Ligong; Chen, Ning; Su, Wei; Wu, Yongcheng; Zhang, Yu (AMER PHYSICAL SOC, 2018-06-07)

The scenario of two mass-degenerate Higgs bosons within the general two-Higgs-doublet model (2HDM) is revisited. We focus on the global picture when two CP-even Higgs bosons of h and H are nearly mass-degenerate. A global fit to the signal strength of the 125 GeV Higgs measured at the LHC is performed. Based on the best-fit result of the 2HDM mixing angles (alpha, beta), theoretical constraints, charged and CP-odd Higgs boson direct search constraints and the electroweak precision constraints are imposed to the 2HDM parameter space. We present the signal predictions of the (4b, 2b2 gamma) channels for the benchmark models at the LHC 14 TeV runs. We also study the direct Higgs boson pair productions at the LHC, and the Z-associated Higgs boson pair production search at the ILC 500 GeV runs, as well as the indirect probes at the CEPC 250 GeV run. We find that the massdegenerate Higgs boson scenario in the Type-II 2HDM can be fully probed by these future experimental searches.

Search for top squarks decaying to tau sleptons in pp collisions at root s=13 TeV with the ATLAS detector

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, 2018-08-16)

A search for direct pair production of top squarks in final states with two tau leptons, b-jets, and missing transverse momentum is presented. The analysis is based on proton-proton collision data at root s = 13 TeV corresponding to an integrated luminosity of 36.1 fb(-1) recorded with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. Two exclusive channels with either two hadronically decaying tau leptons or one hadronically and one leptonically decaying tau lepton are considered. No significant deviation from the Standard Model predictions is observed in the data. The analysis results are interpreted in terms of model-independent limits and used to derive exclusion limits on the masses of the top squark (t) over tilde (1) and the tau slepton (tau) over tilde (1) in a simplified model of supersymmetry with a nearly massless gravitino. In this model, masses up to m((t) over tilde (1)) = 1.16 TeV and m ((tau) over tilde (1)) = 1.00 TeV are excluded at 95% confidence level.

Density split statistics: Cosmological constraints from counts and lensing in cells in DES Y1 and SDSS data

Gruen, D.; Friedrich, O.; Krause, E.; DeRose, J.; Cawthon, R.; Davis, C.; Elvin-Poole, J.; Rykoff, E. S.; Wechsler, R. H.; Alarcon, A.; et al. (AMER PHYSICAL SOC, 2018-07-13)

We derive cosmological constraints from the probability distribution function (PDF) of evolved large-scale matter density fluctuations. We do this by splitting lines of sight by density based on their count of tracer galaxies, and by measuring both gravitational shear around and counts-in-cells in overdense and underdense lines of sight, in Dark Energy Survey (DES) First Year and Sloan Digital Sky Survey (SDSS) data. Our analysis uses a perturbation theory model [O. Friedrich et al., Phys. Rev. D 98, 023508 (2018)] and is validated using N-body simulation realizations and log-normal mocks. It allows us to constrain cosmology, bias and stochasticity of galaxies with respect to matter density and, in addition, the skewness of the matter density field. From a Bayesian model comparison, we find that the data weakly prefer a connection of galaxies and matter that is stochastic beyond Poisson fluctuations on <= 20 arcmin angular smoothing scale. The two stochasticity models we fit yield DES constraints on the matter density Omega(m) = 0.26(-0.04)(+0.05) and Omega(m) = 0.28(-0.03)(+0.04) that are consistent with each other. These values also agree with the DES analysis of galaxy and shear two-point functions (3x2pt, DES Collaboration et al.) that only uses second moments of the PDF. Constraints on s 8 are model dependent (sigma(8) = 0.97(-0.06)(+0.07) and 0.80(-0.07)(+0.06) for the two stochasticity models), but consistent with each other and with the 3 x 2pt results if stochasticity is at the low end of the posterior range. As an additional test of gravity, counts and lensing in cells allow to compare the skewness S-3 of the matter density PDF to its Lambda CDM prediction. We find no evidence of excess skewness in any model or data set, with better than 25 per cent relative precision in the skewness estimate from DES alone.

Search for squarks and gluinos in final states with jets and missing transverse momentum using 36 fb(-1) of root s=13 TeV pp collision data with the ATLAS detector

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, 2018-06-06)

A search for the supersymmetric partners of quarks and gluons (squarks and gluinos) in final states containing hadronic jets and missing transverse momentum, but no electrons or muons, is presented. The data used in this search were recorded in 2015 and 2016 by the ATLAS experiment in root s = 13 TeV proton-proton collisions at the Large Hadron Collider, corresponding to an integrated luminosity of 36.1 fb(-1). The results are interpreted in the context of various models where squarks and gluinos are pair produced and the neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 2.03 TeV for a simplified model incorporating only a gluino and the lightest neutralino, assuming the lightest neutralino is massless. For a simplified model involving the strong production of mass-degenerate first-and second-generation squarks, squark masses below 1.55 TeVare excluded if the lightest neutralino is massless. These limits substantially extend the region of supersymmetric parameter space previously excluded by searches with the ATLAS detector.

Search for resonances in the mass distribution of jet pairs with one or two jets identified as b-jets 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, 2018-08-30)

A search for new resonances decaying into jets containing b-hadrons in pp collisions with the ATLAS detector at the LHC is presented in the dijet mass range from 0.57 to 7 TeV. The data set corresponds to an integrated luminosity of up to 36.1 fb(-1) collected in 2015 and 2016 at root s = 13 TeV. No evidence of a significant excess of events above the smooth background shape is found. Upper cross-section limits and lower limits on the corresponding signal mass parameters for several types of signal hypotheses are provided at 95% C.L. In addition, 95% C.L. upper limits are set on the cross sections for new processes that would produce Gaussian-shaped signals in the di-b-jet mass distributions.

Effects of nonequilibrated topological charge distributions on pseudoscalar meson masses and decay constants

Bernard, C.; Toussaint, D. (AMER PHYSICAL SOC, 2018-04-02)

We study the effects of failure to equilibrate the squared topological charge Q(2) on lattice calculations of pseudoscalar masses and decay constants. The analysis is based on chiral perturbation theory calculations of the dependence of these quantities on the QCD vacuum angle theta. For the light-light partially quenched case, we rederive the known chiral perturbation theory results of Aoki and Fukaya, but using the nonperturbatively valid chiral theory worked out by Golterman, Sharpe and Singleton, and by Sharpe and Shoresh. We then extend these calculations to heavy-light mesons. Results when staggered taste violations are important are also presented. The derived Q(2) dependence is compared to that of simulations using the MILC Collaboration's ensembles of lattices with four flavors of dynamical highly improved staggered quarks. We find agreement, albeit with large statistical errors. These results can be used to correct for the leading effects of unequilibrated Q(2), or to make estimates of the systematic error coming from the failure to equilibrate Q(2). In an appendix, we show that the partially quenched chiral theory may be extended beyond a lower bound on valence masses discovered by Sharpe and Shoresh. Subtleties occurring when a sea-quark mass vanishes are discussed in another appendix.

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).

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.

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