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Search Results: 1 - 10 of 415026 matches for " Andrew M Laycock "
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Extended Inflation with a Curvature-Coupled Inflaton
Andrew M Laycock,Andrew R Liddle
Physics , 1993, DOI: 10.1103/PhysRevD.49.1827
Abstract: We examine extended inflation models enhanced by the addition of a coupling between the inflaton field and the space-time curvature. We examine two types of model, where the underlying inflaton potential takes on second-order and first-order form respectively. One aim is to provide models which satisfy the solar system constraints on the Brans--Dicke parameter $\omega$. This constraint has proven very problematic in previous extended inflation models, and we find circumstances where it can be successfully evaded, though the constraint must be carefully assessed in our model and can be much stronger than the usual $\omega > 500$. In the simplest versions of the model, one may avoid the need to introduce a mass for the Brans--Dicke field in order to ensure that it takes on the correct value at the present epoch, as seems to be required in hyperextended inflation. We also briefly discuss aspects of the formation of topological defects in the inflaton field itself.
A Transient Supergiant X-ray Binary in IC10. An Extragalactic SFXT?
Silas Laycock,Rigel Cappallo,Kathleen Oram,Andrew Balchunas
Physics , 2014, DOI: 10.1088/0004-637X/789/1/64
Abstract: We report the discovery of a large amplitude (factor of $\sim$100) X-ray transient (IC 10 X-2, CXOU J002020.99+591758.6) in the nearby dwarf starburst galaxy IC10 during our Chandra monitoring project. Based on the X-ray timing and spectral properties, and an optical counterpart observed with Gemini, the system is a high mass X-ray binary (HMXB) consisting of a luminous blue supergiant and a neutron star (NS). The highest measured luminosity of the source was 1.8$\times$10$^{37}$ erg s$^{-1}$ during an outburst in 2003. Observations before, during and after a second outburst in 2010 constrain the outburst duration to be less than 3 months (with no lower limit). The X-ray spectrum is a hard powerlaw ($\Gamma$=0.3) with fitted column density ($N_H$=6.3$\times$10$^{21}$ atom cm$^{-2}$) consistent with the established absorption to sources in IC10. The optical spectrum shows hydrogen Balmer lines strongly in emission, at the correct blueshift (-340 km/s) for IC10. The NIII triplet emission feature is seen, accompanied by He II [4686] weakly in emission. Together these features classify the star as a luminous blue supergiant of the OBN subclass, characterized by enhanced nitrogen abundance. Emission lines of HeI are seen, at similar strength to H$\beta$. A complex of FeII permitted and forbidden emission lines are seen, as in B[e] stars. The system closely resembles galactic supergiant fast X-ray transients (SFXTs), in terms of its hard spectrum, variability amplitude and blue supergiant primary.
Revisiting the Dynamical Case for a Massive Black Hole in IC10 X-1
Silas G. T. Laycock,Thomas J. Maccarone,Dimitris M. Christodoulou
Physics , 2015, DOI: 10.1093/mnrasl/slv082
Abstract: The relative phasing of the X-ray eclipse ephemeris and optical radial velocity (RV) curve for the X-ray binary IC10 X-1 suggests the He[$\lambda$4686] emission-line originates in a shadowed sector of the stellar wind that avoids ionization by X-rays from the compact object. The line attains maximum blueshift when the wind is directly toward us at mid X-ray eclipse, as is also seen in Cygnus X-3. If the RV curve is unrelated to stellar motion, evidence for a massive black hole evaporates because the mass function of the binary is unknown. The reported X-ray luminosity, spectrum, slow QPO, and broad eclipses caused by absorption/scattering in the WR wind are all consistent with either a low-stellar-mass BH or a NS. For a NS, the centre of mass lies inside the WR envelope whose motion is then far below the observed 370 km/s RV amplitude, while the velocity of the compact object is as high as 600 km/s. The resulting 0.4\% doppler variation of X-ray spectral lines could be confirmed by missions in development. These arguments also apply to other putative BH binaries whose RV and eclipse curves are not yet phase-connected. Theories of BH formation and predicted rates of gravitational wave sources may need revision.
The Magnetic Field of the Ultraluminous X-ray Pulsar M82 X-2
Dimitris M. Christodoulou,Silas G. T. Laycock,Demosthenes Kazanas
Physics , 2014,
Abstract: Pulsations were recently detected from the ultraluminous X-ray source X-2 in M82. The newly discovered pulsar has been described as a common neutron star with a 1 TG magnetic field that accretes above the Eddington rate and as a magnetar-like pulsar with a 100 TG magnetic field that is above the quantum limit. We show here that this X-ray source is not exotic in any sense. The standard equations of accretion along field lines predict that, for the measured spin period $P_S$ and spinup rate $\dot{P_S}$, the isotropic X-ray luminosity $L_X$ must be near the Eddington limit (i.e., $L_{X}\approx 3.5\times 10^{38}$~erg~s$^{-1}$); and that the surface magnetic field $B$, that does not depend on $P_S$, must be modest (i.e., $B_*\approx 1-10$ TG). The observed higher luminosity can be explained by a moderate amount of geometric beaming that occurs in our direction. Other ultraluminous X-ray sources may also turn out to be common pulsars with similar physical characteristics, but since the emission must occur at a favorable angle to the observer, we expect that very few such pulsars will be discovered in the future.
Editorial introduction to 'Opportunity makes the thief. Really? And so what?'
Gloria Laycock
Crime Science , 2012, DOI: 10.1186/2193-7680-1-2
Abstract:
Words without Objects
Henry Laycock
Principia : an International Journal of Epistemology , 1998,
Abstract: Resolution of the problem of mass nouns depends on an expansion of our semantic/ontological taxonomy. Semantically, mass nouns are neither singular nor plural; they apply to neither just one object, nor to many objects, at a time. But their deepest kinship links them to the plural. A plural phrase — 'the cats in Kingston' — does not denote a single plural thing, but merely many distinct things. Just so, 'the water in the lake' does not denote a single aggregate — it is not ONE, but rather MUCH. The world is not the totality of singular objects, plural objects, and mass objects; for there are no plural or mass objects. It is the totality of single objects and (just) stuff.
Inclusive Diffraction at HERA
Paul Laycock
Physics , 2008,
Abstract: The H1 and Zeus collaborations have measured the inclusive diffractive DIS cross section ep -> eXp and these measurements are in good agreement within a normalisation uncertainty. Diffractive parton density functions (DPDFs) have been extracted from NLO QCD fits to inclusive measurements of diffractive DIS and the predictions of these DPDFs are compared with measurements of diffractive dijets in DIS, testing the validity of the factorisation approximations used in their extraction. H1 then use these diffractive dijets in DIS data to provide further constraints in a combined QCD fit, resulting in the next generation of DPDFs which have constrained the diffractive gluon at large momentum fractions. Finally, the predictions of DPDFs are compared to diffractive dijets in photoproduction where the issue of survival probability in a hadron-hadron environment can be studied.
Diffraction at H1 and Zeus
Paul Laycock
Physics , 2009,
Abstract: The H1 and Zeus collaborations have measured the inclusive diffractive DIS cross section ep -> eXp and these measurements are in good agreement within a normalisation uncertainty. Diffractive parton density functions (DPDFs) have been extracted from NLO QCD fits to these data and the predictions of these DPDFs compare well with measurements of diffractive dijets in DIS, proving the validity of the factorisation approximations used in their extraction. The inclusive and dijet data are then used in a combined fit to constrain the diffractive singlet and gluon with good precision over the full phase space. The predictions of DPDFs are compared to diffractive dijets in photoproduction where the issue of survival probability in a hadron-hadron environment can be studied. Finally, exclusive diffractive vector meson production and deeply virtual Compton scattering have also been studied; the results compare reasonably well with the expectations of QCD and in particular with GPD models.
Diffractive Structure Functions with H1
Paul Laycock
Physics , 2012,
Abstract: H1 has measured the diffractive DIS cross section $ep \rightarrow eXY$ using data from both of the HERA data-taking periods. Using new measurements of the diffractive cross section at different centre-of-mass energies, the diffractive longitudinal structure function $F_L^D$ has been extracted. The results are in agreement with NLO QCD predictions based on fits to inclusive data. New high statistics measurements of the diffractive reduced cross section $\sigma_r^D$ have been made using two experimental methods covering the accessible kinematic range. This precise dataset agrees well with QCD-based predictions.
10 Years of Object-Oriented Analysis on H1
Paul Laycock
Physics , 2012, DOI: 10.1088/1742-6596/368/1/012048
Abstract: Over a decade ago, the H1 Collaboration decided to embrace the object-oriented paradigm and completely redesign its data analysis model and data storage format. The event data model, based on the RooT framework, consists of three layers - tracks and calorimeter clusters, identified particles and finally event summary data - with a singleton class providing unified access. This original solution was then augmented with a fourth layer containing user-defined objects. This contribution will summarise the history of the solutions used, from modifications to the original design, to the evolution of the high-level end-user analysis object framework which is used by H1 today. Several important issues are addressed - the portability of expert knowledge to increase the efficiency of data analysis, the flexibility of the framework to incorporate new analyses, the performance and ease of use, and lessons learned for future projects.
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