18512510
Higgs boson production with one bottom quark including higher-order soft-gluon corrections
A Higgs boson produced in association with one or more bottom quarks is of great theoretical and experimental interest to the high-energy community. A precise prediction of its total and differential cross section can have a great impact on the discovery of a Higgs boson with large bottom-quark Yukawa coupling, like the scalar (h{sup 0} and H{sup 0}) and pseudoscalar (A{sup 0}) Higgs bosons of the minimal supersymmetric standard model in the region of large tan{beta}. In this paper we apply the threshold resummation formalism to determine both differential and total cross sections for bg{yields}b{phi} (where {phi}=h{sup 0},H{sup 0}), including up to next-to-next-to-next-to-leading order soft plus virtual QCD corrections at next-to-leading logarithmic accuracy. We present results for both the Fermilab Tevatron and the CERN Large Hadron Collider.
119249502
Gamma rays from top-mediated dark matter annihilations
Lines in the energy spectrum of gamma rays are a fascinating experimental signal, which are often considered ''smoking gun" evidence of dark matter annihilation. The current generation of gamma ray observatories are currently closing in on parameter space of great interest in the context of dark matter which is a thermal relic. We consider theories in which the dark matter's primary connection to the Standard Model is via the top quark, realizing strong gamma ray lines consistent with a thermal relic through the forbidden channel mechanism proposed in the Higgs in Space Model. We consider realistic UV-completions of the Higgs in Space and related theories, and show that a rich structure of observable gamma ray lines is consistent with a thermal relic as well as constraints from dark matter searches and the LHC. Particular attention is paid to the one loop contributions to the continuum gamma rays, which can easily swamp the line signals in some cases, and have been largely overlooked in previous literature.
3163182
Higgs-Pair Production and Measurement of the Triscalar Coupling at LHC(8,14)
Abstract We simulate the measurement of the triscalar Higgs coupling at LHC ( 8 , 14 ) via pair production of h (125 GeV). We find that the most promising hh final state is b b ¯ γ γ . We account for deviations of the triscalar coupling from its SM value and study the effects of this coupling on the hh cross-section and distributions with cut-based and multivariate methods. Our fit to the hh production matrix element at LHC(14) with 3 ab − 1 yields a 30% uncertainty on this coupling in the SM and a range of 20–60% uncertainties for non-SM values.
118342809
Gamma ray lines from a universal extra dimension
Indirect Dark Matter searches are based on the observation of secondary particles produced by the annihilation or decay of Dark Matter. Among them, gamma-rays are perhaps the most promising messengers, as they do not suffer deflection or absorption on Galactic scales, so their observation would directly reveal the position and the energy spectrum of the emitting source. Here, we study the detailed gamma-ray energy spectrum of Kaluza-Klein Dark Matter in a theory with 5 Universal Extra Dimensions. We focus in particular on the two body annihilation of Dark Matter particles into a photon and another particle, which produces monochromatic photons, resulting in a line in the energy spectrum of gamma rays. Previous calculations in the context of the five dimensional UED model have computed the line signal from annihilations into ??, but we extend these results to include ?Z and ?H final states. We find that these spectral lines are subdominant compared to the predicted ?? signal, but they would be important as follow-up signals in the event of the observation of the ?? line, in order to distinguish the 5d UED model from other theoretical scenarios.
27307688
New physics in resonant production of Higgs boson pairs.
We advocate a search for an extended scalar sector at the LHC via hh production, where h is the 125 GeV Higgs boson. A resonance feature in the hh invariant mass is a smoking gun of an s-channel heavy Higgs resonance, H. With one h decaying to two photons and the other decaying to b quarks, the resonant signal may be discoverable above the hh continuum background for M(H)<1  TeV. The product of the scalar and top Yukawa couplings can be measured to better than 10%-20% accuracy, and its sign can be inferred from the hh line shape via interference effects.
119224735
Gamma-ray lines and One-Loop Continuum from s-channel Dark Matter Annihilations
The era of indirect detection searches for dark matter has begun, with the sensitivities of gamma-ray detectors now approaching the parameter space relevant for weakly interacting massive particles. In particular, gamma ray lines would be smoking gun signatures of dark matter annihilation, although they are typically suppressed compared to the continuum. In this paper, we pay particular attention to the 1-loop continuum generated together with the gamma-ray lines and investigate under which conditions a dark matter model can naturally lead to a line signal that is relatively enhanced. We study generic classes of models in which DM is a fermion that annihilates through an s-channel mediator which is either a vector or scalar and identify the coupling and mass conditions under which large line signals occur. We focus on the \forbidden channel mechanism" advocated a few years ago in the \Higgs in space" scenario for which tree level annihilation is kinematically forbidden today. Detailed calculations of all 1-loop annihilation channels are provided. We single out very simple models with a large line over continuum ratio and present general predictions for a large range of WIMP masses that are relevant not only for Fermi and Hess II but also for the next generation of telescopes such as CTA and Gamma-400. Constraints from the relic abundance, direct detection and collider bounds are also discussed.
15407740
The Parkes quarter-Jansky flat-spectrum sample. 2. New optical spectra and redshift measurements
We present optical spectra and redshift measurements for 178 flat-spectrum objects from the Parkes quarter-Jansky flat-spectrum sample. These spectra were obtained in order to compile a complete sample of quasars for use in a study of quasar evolution. We present a composite optical spectrum made from the subset of 109 quasars that have flux densities in the range 0.25 Jy < S 2 . 7 G H z < 0.5 Jy, and make a comparison with a composite for radio-quiet QSOs from the Large Bright Quasar Survey. Our large sample of radio-loud quasars allows us to strengthen previous reports that the Lya and CIV emission lines have larger equivalent width in radio-loud quasars than radio-quiet QSOs to greater than the 3σ level. However we see no significant difference in the equivalent widths of CIII] or MgII. We also show that the flux decrements across the Lyman-α line (D A ) measured from these spectra show the same trend with redshift as for optically selected QSOs.
119069361
Radio Observations of the Hubble Deep Field South region: I. Survey Description and Initial Results
This paper is the first of a series describing the results of the Australia Telescope Hubble Deep Field–South radio survey. The survey was conducted at four wavelengths, 20, 11, 6, and 3 cm, over a 4 year period and achieves an rms sensitivity of about 10 μJy at each wavelength. We describe the observations and data reduction processes and present data on radio sources close to the center of the Hubble Deep Field–South. We discuss in detail the properties of a subset of these sources. The sources include both starburst galaxies and galaxies powered by an active galactic nucleus and range in redshift from 0.1 to 2.2. Some of them are characterized by unusually high radio-to-optical luminosities, presumably caused by dust extinction.
209835469
Radio observations of the hubble deep field-south region. IV. Optical properties of the faint radio population
The Australia Telescope Hubble Deep Field-South (ATHDF-S) survey of the Hubble Deep Field-South (HDF-S) reaches sensitivities of ~10 μJy at 1.4, 2.5, 5.2, and 8.7 GHz, making the ATHDF-S one of the deepest surveys ever performed with the Australia Telescope Compact Array (ATCA). Here, we present the optical identifications of the ATHDF-S radio sources using data from the literature. We find that ~66% of the radio sources have optical counterparts to I = 23.5 mag. Deep Hubble Space Telescope (HST) imaging of the area identifies a further 12% of radio sources. We present new spectroscopic observations for 98 of the radio sources and supplement these spectroscopic redshifts with photometric ones calculated from five-band optical imaging. The host galaxy colors and radio-to-optical ratios indicate that low-luminosity (or "radio-quiet") active galactic nuclei make up a significant proportion of the sub-mJy radio population, a result which is in accordance with a number of other deep radio studies. The radio-to-optical ratios of the bright (S 1.4 GHz > 1 mJy) sources are consistent with a bimodal distribution.
14405311
First results from the ATCA 18 GHz pilot survey
ABSTRACT As a pilot study for the ﬁrst all–sky radio survey at short wavelengths, we have ob-served 1216deg 2 of the southern sky at 18GHz (16mm) using a novel wide–band(3.4GHz bandwidth) analogue correlator on one baseline of the Australia TelescopeCompact Array (ATCA). We scanned a region of sky between declination −71 ◦ and−59 ◦ with an rms noise level of 15mJy. Follow–up radio imaging of candidate sourcesabove a 4σ detection limit of 60mJy resulted in 221 conﬁrmed detections, for whichwe have measured accurate positions and ﬂux densities. For extragalactic sources, thesurvey is roughly 70% complete at a ﬂux density of 126mJy and 95% complete above300mJy. Almosthalfthe detected sourceslie within a few degreesofthe Galacticplane,but there are 123 sources with |b| > 5 ◦ which can be assumed to be extragalactic. Thediﬀerential source counts for extragalactic sources in the range 0.1Jy ≤ S 18GHz ≤ 3Jyare well ﬁtted by a relation of the form n(S) = 57(S/Jy) − 2.±0 Jy −1 sr 1 , in goodagreement with the 15GHz counts published by Taylor et al. (2001) and Waldramet al. (2003). Over 70% of the extragalactic sources have a ﬂat radio spectrum(α
14495212
Deep radio continuum studies with the SKA: evolution of radio AGN populations
Abstract Radio emission is insensitive to dust obscuration, and the breadth of the radio luminosity function ensures that sources are detected over a wide range of redshifts at all radio flux densities. As a result, radio continuum observations are an efficient and unbiased probe of both nuclear (AGN) and star-forming activity over all cosmic epochs. The SKA’s ultra-deep radio continuum surveys will provide the answers to at least three key astrophysical questions: (i) the star-formation history of the Universe, (ii) the evolution of the low-power end of the radio galaxy luminosity function and (iii) the relationship between the radio-loud AGN, star-formation and radio-quiet AGN phenomena. In this paper, we discuss the AGN science that will be enabled by the deep radio continuum studies using the SKA. It is important to recognise that the sub-μJy SKA sky will be dominated by populations other than ‘radio-loud’ AGN. In this way the SKA will not only provide an unbiased tracer of the star-formation history of the Universe but also be able to study the populations of sources we currently describe as ‘radio-quiet’. To illustrate this point we present simulations of the extragalactic radio sky based from models of the evolution of the radio luminosity function. From these simulations we predict typical source distributions and estimate the natural confusion limit to ultra-faint flux density limits relevant to the science and design goals of the SKA.