203 research outputs found
Interior potential of a toroidal shell from pole values
We have investigated the toroidal analog of ellipsoidal shells of matter,
which are of great significance in Astrophysics. The exact formula for the
gravitational potential of a shell with a circular section at the
pole of toroidal coordinates is first established. It depends on the mass of
the shell, its main radius and axis-ratio (i.e. core-to-main radius ratio),
and involves the product of the complete elliptic integrals of the first and
second kinds. Next, we show that successive partial derivatives are also accessible by analytical means
at that singular point, thereby enabling the expansion of the interior
potential as a bivariate series. Then, we have generated approximations at
orders , , and , corresponding to increasing accuracy. Numerical
experiments confirm the great reliability of the approach, in particular for
small-to-moderate axis ratios ( typically). In contrast with
the ellipsoidal case (Newton's theorem), the potential is not uniform inside
the shell cavity as a consequence of the curvature. We explain how to construct
the interior potential of toroidal shells with a thick edge (i.e. tubes), and
how a core stratification can be accounted for. This is a new step towards the
full description of the gravitating potential and forces of tori and rings.
Applications also concern electrically-charged systems, and thus go beyond the
context of gravitation.Comment: Accepted for publication in MNRA
Static and radiating p -form black holes in the higher dimensional Robinson-Trautman class
We study Robinson-Trautman spacetimes in the presence of an aligned p -form Maxwell field and an arbitrary cosmological constant in n ≥ 4 dimensions. As it turns out, the character of these exact solutions depends significantly on the (relative) value of n and p . In odd dimensions the solutions reduce to static black holes dressed with an electric and a magnetic field, with an Einstein space horizon (further constrained by the Einstein-Maxwell equations) — both the Weyl and Maxwell types are D. Even dimensions, however, open up more possibilities. In particular, when 2 p = n there exist non-static solutions describing black holes gaining (or losing) mass by receiving (or emitting) electromagnetic radiation. In this case the Weyl type is II (D) and the Maxwell type can be II (D) or N. Conditions under which the Maxwell field is self-dual (for odd p ) are also discussed, and a few explicit examples presented. Finally, the case p = 1 is special in all dimensions and leads to static metrics with a non-Einstein transverse space
Mirror Development for the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) is a planned observatory for very-high
energy gamma-ray astronomy. It will consist of several tens of telescopes of
different sizes, with a total mirror area of up to 10,000 square meters. Most
mirrors of current installations are either polished glass mirrors or
diamond-turned aluminium mirrors, both labour intensive technologies. For CTA,
several new technologies for a fast and cost-efficient production of
light-weight and reliable mirror substrates have been developed and industrial
pre-production has started for most of them. In addition, new or improved
aluminium-based and dielectric surface coatings have been developed to increase
the reflectance over the lifetime of the mirrors compared to those of current
Cherenkov telescope instruments
Gauge independence in a higher-order Lagrangian formalism via change of variables in the path integral
In this paper we work out the explicit form of the change of variables that reproduces an arbitrary change of gauge in a higher-order Lagrangian formalism
Measurement of the forward charged particle pseudorapidity density in pp collisions at s=8 TeV using a displaced interaction point
The pseudorapidity density of charged particles dN ch /d η is measured by the TOTEM experiment in proton–proton collisions at s=8 TeV within the range 3.9<η<4.7 and -6.95<η<-6.9 . Data were collected in a low intensity LHC run with collisions occurring at a distance of 11.25 m from the nominal interaction point. The data sample is expected to include 96–97 % of the inelastic proton–proton interactions. The measurement reported here considers charged particles with pT>0 MeV/c, produced in inelastic interactions with at least one charged particle in -7<η<-6 or 3.7<η<4.8 . The dN ch /d η has been found to decrease with |η| , from 5.11 ± 0.73 at η=3.95 to 1.81 ± 0.56 at η=- 6.925. Several Monte Carlo generators are compared to the data and are found to be within the systematic uncertainty of the measurement
Evidence for non-exponential elastic proton–proton differential cross-section at low |t| and s=8TeV by TOTEM
The TOTEM experiment has made a precise measurement of the elastic proton–proton differential cross-section at the centre-of-mass energy s=8 TeV based on a high-statistics data sample obtained with the β⁎=90 m optics. Both the statistical and systematic uncertainties remain below 1%, except for the t -independent contribution from the overall normalisation. This unprecedented precision allows to exclude a purely exponential differential cross-section in the range of four-momentum transfer squared 0.027<|t|<0.2 GeV2 with a significance greater than 7 σ . Two extended parametrisations, with quadratic and cubic polynomials in the exponent, are shown to be well compatible with the data. Using them for the differential cross-section extrapolation to t=0 , and further applying the optical theorem, yields total cross-section estimates of (101.5±2.1) mb and (101.9±2.1) mb , respectively, in agreement with previous TOTEM measurements
Baryon resonance production and dielectron decays in proton-proton collisions at 3.5 GeV
We report on baryon resonance production and decay in proton-proton
collisions at a kinetic energy of GeV based on data measured with HADES.
The exclusive channels and as well as are studied simultaneously
for the first time. The invariant masses and angular distributions of the
pion-nucleon systems were studied and compared to simulations based on a
resonance model ansatz assuming saturation of the pion production by an
incoherent sum of baryonic resonances (R) with masses GeV/. A very
good description of the one-pion production is achieved allowing for an
estimate of individual baryon-resonance production-cross-sections which are
used as input to calculate the dielectron yields from
decays. Two models of the resonance decays into dielectrons are examined
assuming a point-like coupling and the dominance of the
meson. The results of model calculations are compared to data from the
exclusive channel by means of the dielectron and
invariant mass distributions
Searching a dark photon with HADES
We present a search for the <math altimg="si1.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></math> decay of a hypothetical dark photon, also named U vector boson, in inclusive dielectron spectra measured by HADES in the p(3.5 GeV) + p, Nb reactions, as well as the Ar ( <math altimg="si2.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mn>1.756</mn><mtext> GeV</mtext><mo stretchy="false">/</mo><mtext>u</mtext></math> ) + KCl reaction. An upper limit on the kinetic mixing parameter squared <math altimg="si3.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msup><mrow><mi>ϵ</mi></mrow><mrow><mn>2</mn></mrow></msup></math> at 90% CL has been obtained for the mass range <math altimg="si4.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>M</mi></mrow><mrow><mi>U</mi></mrow></msub><mo>=</mo><mn>0.02</mn><mtext>–</mtext><mn>0.55</mn><mtext> GeV</mtext><mo stretchy="false">/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></math> and is compared with the present world data set. For masses <math altimg="si5.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mn>0.03</mn><mtext>–</mtext><mn>0.1</mn><mtext> GeV</mtext><mo stretchy="false">/</mo><msup><mrow><mi>c</mi></mrow><mrow><mn>2</mn></mrow></msup></math> , the limit has been lowered with respect to previous results, allowing now to exclude a large part of the parameter region favored by the muon <math altimg="si6.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mi>g</mi><mo>−</mo><mn>2</mn></math> anomaly. Furthermore, an improved upper limit on the branching ratio of <math altimg="si7.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mn>2.3</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>6</mn></mrow></msup></math> has been set on the helicity-suppressed direct decay of the eta meson, <math altimg="si8.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mi>η</mi><mo stretchy="false">→</mo><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></math> , at 90% CL
Diffractive dijet production with a leading proton in ep collisions at HERA
The cross section of the diffractive process e + p → e + Xp is measured at a centre-of-mass energy of 318 GeV, where the system X contains at least two jets and the leading final state proton p is detected in the H1 Very Forward Proton Spectrometer. The measurement is performed in photoproduction with photon virtualities Q 2 < 2 GeV 2 and in deep-inelastic scattering with 4 GeV 2 < Q 2 < 80 GeV 2 . The results are compared to next- to-leading order QCD calculations based on diffractive parton distribution functions as extracted from measurements of inclusive cross sections in diffractive deep-inelastic scattering
Measurement of dijet production in diffractive deep-inelastic ep scattering at HERA
A measurement is presented of single- and double-differential dijet cross sections in diffractive deep-inelastic ep scattering at HERA using data collected by the H1 experiment corresponding to an integrated luminosity of 290 pb −1 . The investigated phase space is spanned by the photon virtuality in the range of 4 < Q 2 < 100 GeV 2 and by the fractional proton longitudinal momentum loss x ℙ < 0 . 03. The resulting cross sections are compared with next-to-leading order QCD predictions based on diffractive parton distribution functions and the value of the strong coupling constant is extracted
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