1,055 research outputs found
First XMM-Newton study of two Narrow-Line Seyfert 1 galaxies discovered in the Sloan Digital Sky Survey
The Early Data Release of the Sloan Digital Sky Survey (SDSS) contains 150
Narrow-Line Seyfert 1 (NLS1) galaxies, most of them previously unknown. We
present here the study of the X-ray emission from two of these active galaxies
(SDSS J030639.57+000343.2 and SDSS J141519.50-003021.6), based upon XMM-Newton
observations. The spectral and timing characteristics of the two sources are
presented and compared against the typical properties of known NLS1 galaxies.
We found that these two NLS1 are within the dispersion range of the typical
values of this class of AGN, although with some interesting features that
deserve further studies.Comment: 5 pages, 8 figures. Accepted for publication on A&A Main Journa
Hybrid natural inflation from non Abelian discrete symmetry
A spontaneously broken global discrete symmetry may have pseudo Goldstone
modes associated with the spontaneous breaking of the approximate continuous
symmetry of the low dimension terms in the Lagrangian. These provide natural
candidates for an inflaton that can generate slow roll inflation. We show that,
in the case of a non Abelian discrete symmetry, the pseudo Goldstone modes
readily couple to further scalar fields in a manner that the end of inflation
is determined by these additional scalar fields, generating hybrid inflation.
We give a simple parameterisation of the inflationary potential in this case,
determine the inflationary parameters resulting, and show that phenomenological
successful inflation is possible while keeping the scale of symmetry breaking
sub-Plankian. Unlike natural inflation the inflation scale can be very low. We
construct two simple hybrid inflation models, one non supersymmetric and one
supersymmetric. In the latter case no parameters need be chosen anomalously
small.Comment: Accepted for publication in Phys. Lett.
Bounds on R-Parity Violating Parameters from Fermion EDM's
We study one-loop contributions to the fermion electric dipole moments in the
Minimal Supersymmetric Standard Model with explicit R-parity violating
interactions. We obtain new individual bounds on R-parity violating Yukawa
couplings and put more stringent limits on certain parameters than those
obtained previously.Comment: 16 pages, LaTe
Ross, Macdonald, and a Theory for the Dynamics and Control of Mosquito-Transmitted Pathogens
Ronald Ross and George Macdonald are credited with developing a mathematical model of mosquito-borne pathogen transmission. A systematic historical review suggests that several mathematicians and scientists contributed to development of the Ross-Macdonald model over a period of 70 years. Ross developed two different mathematical models, Macdonald a third, and various “Ross-Macdonald” mathematical models exist. Ross-Macdonald models are best defined by a consensus set of assumptions. The mathematical model is just one part of a theory for the dynamics and control of mosquito-transmitted pathogens that also includes epidemiological and entomological concepts and metrics for measuring transmission. All the basic elements of the theory had fallen into place by the end of the Global Malaria Eradication Programme (GMEP, 1955–1969) with the concept of vectorial capacity, methods for measuring key components of transmission by mosquitoes, and a quantitative theory of vector control. The Ross-Macdonald theory has since played a central role in development of research on mosquito-borne pathogen transmission and the development of strategies for mosquito-borne disease prevention
Flavour-Dependent and Basis Independent Measures of R Violation
We construct lepton flavour-dependent and basis-independent measures of
R-parity violation in the minimal supersymmetric extension of the Standard
Model (MSSM). We work in the context of exact supersymmetry, neglecting the
effects of Higgs vacuum expectation values and soft supersymmetry-breaking
terms. We devote particular attention to appropriate choices of flavour
eigenstates, and to the counting and enumeration of R-violating invariants in
two- and three-generation models. We also make an indicative application of our
results to derive possible basis-independent cosmological upper bounds on
flavour-dependent violation of R parity.Comment: 20 pages, Latex, requires axodraw.st
R parity violating contribution to
In this article we consider the contribution of violating couplings to
the process at high energy lepton collider.
We show that the present upper bound on the relevant violating coulpings
obtained from low energy measurements would produce a few hundred to a thousand
top-charm events at the next linear collider. Hence, it
should be possible to observe the rare process at future lepton collider.Comment: LaTEX, 13 pages, one figure is removed. A brief discussion on
possible backgrounds is added. To appear in Phys. Rev.
XMM-Newton and Suzaku analysis of the Fe K complex in the Seyfert 1 galaxy Mrk 509
We report on partially overlapping XMM-Newton (~260 ks) and Suzaku (~100 ks)
observations of the iron K band in the nearby, bright Seyfert 1 galaxy Mrk 509.
The source shows a resolved neutral Fe K line, most probably produced in the
outer part of the accretion disc. Moreover, the source shows further emission
blue-ward of the 6.4 keV line due to ionized material. This emission is well
reproduced by a broad line produced in the accretion disc, while it cannot be
easily described by scattering or emission from photo-ionized gas at rest. The
summed spectrum of all XMM-Newton observations shows the presence of a narrow
absorption line at 7.3 keV produced by highly ionized outflowing material. A
spectral variability study of the XMM-Newton data shows an indication for an
excess of variability at 6.6-6.7 keV. These variations may be produced in the
red wing of the broad ionized line or by variation of a further absorption
structure. The Suzaku data indicate that the neutral Fe Kalpha line intensity
is consistent with being constant on long timescales (of a few years) and they
also confirm as most likely the interpretation of the excess blueshifted
emission in terms of a broad ionized Fe line. The average Suzaku spectrum
differs from the XMM-Newton one for the disappearance of the 7.3 keV absorption
line and around 6.7 keV, where the XMM-Newton data alone suggested variability.Comment: MNRAS in pres
Explaining Evidence Denial as Motivated Pragmatically Rational Epistemic Irrationality
This paper introduces a model for evidence denial that explains this behavior as a manifestation of rationality and it is based on the contention that social values (measurable as utilities) often underwrite these sorts of responses. Moreover, it is contended that the value associated with group membership in particular can override epistemic reason when the expected utility of a belief or belief system is great. However, it is also true that it appears to be the case that it is still possible for such unreasonable believers to reverse this sort of dogmatism and to change their beliefs in a way that is epistemically rational. The conjecture made here is that we should expect this to happen only when the expected utility of the beliefs in question dips below a threshold where the utility value of continued dogmatism and the associated group membership is no longer sufficient to motivate defusing the counter-evidence that tells against such epistemically irrational beliefs
Pursuing interpretations of the HERA large-Q2 data
We explore interpretations of the anomaly observed by H1 and ZEUS at HERA in
deep-inelastic e^+ p scattering at very large Q^2. We discuss the possibilities
of new effective interactions and the production of a narrow state of mass 200
GeV with leptoquark couplings. We compare these models with the measured Q^2
distributions: for the contact terms, constraints from LEP2 and the Tevatron
allow only a few choices of helicity and flavour structure that could roughly
fit the HERA data. The data are instead quite consistent with the Q^2
distribution expected from a leptoquark state. We study the production cross
sections of such a particle at the Tevatron and at HERA. The absence of a
signal at the Tevatron disfavours the likelihood that any such leptoquark
decays only into e^+ q. We then focus on the possibility that the leptoquark is
a squark with R-violating couplings. In view of the present experimental limits
on such couplings, the most likely production channels are e^+d -> scharm_L or
perhaps e^+d->stop, with e^+s->stop a more marginal possibility. Possible tests
of our preferred model include the absence both of analogous events in e^- p
collisions and of charged current events, and the presence of detectable
cascade decays whose kinematical signatures we discuss. We also discuss the
possible implications for K->pi nu nubar, neutrinoless double-beta decay, the
Tevatron and for e^+ e^- ->q qbar and neutralinos at LEP2.Comment: 28 pages, Latex, epsfig, 8 figures. Note added on contact term
HERA Data and Leptoquarks in Supersymmetry
I present a concise review of the possible evidence for new physics at HERA
and of the recent work towards a theoretical interpretation of the signal. It
is not clear yet if the excess observed at large Q^2 is a resonance or a
continuum (this tells much about the quality of the signal). I discuss both
possibilities. For the continuum case one considers either modifications of the
quark structure functions or contact terms. In the case of a resonance, a
leptoquark, the most attractive possibility that is being studied is in terms
of s-quarks with R-parity violation. In writing this script I updated the
available information to include the new data and the literature presented up
to August 1, 1997.Comment: 10 pages, LaTeX, uses fleqn,twoside,espcrc2, Talk given at SUSY'9
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