Dr. Janson wins NASA's 2017 Innovative Advanced Concepts Phase II award for his teams proposal of Brane Craft, a thinner-than-human-hair spacecraft hoping to gather space debris and bring it safe back into atmosphere.
Read More
“This is a very diverse company that hires engineers and scientists with very different backgrounds. Your working experience is highly dependent on the group you end up working with.”
In 1977, The Aerospace Corporation established the Robert H. Herndon Memorial Science Competition. This event provides middle and high school students in Los Angeles County an opportunity to participate annually in the El Segundo portion of the essay and/or science experiment competition. In 2000, a Washington-area Herndon Memorial Science Competition was established and is also held annually.
Learn MoreIntroductory paragraph, instead we present a well-defined series expansion that makes it possible to find analytic solutions order by order in the expansion parameter: it is well known that the time average of the product of two functions is not in general the product of the time averages of those functions, and also that a scalar field is not a perfect fluid [8], so one needs to take some care with the standard procedure.
Default paragraph style, for those modes larger than the Jeans length the scalar field follows the evolution in the standard CDM scenario, except for the large oscillations of the contrast in the energy density for modes larger than the Hubble radius when evaluated in e.g. the conformal-Newtonian gauge. Note however that these (large) oscillations are not present in the behavior of the Newtonian potential, for which the scalar field behaves like CDM, or even in the super-Hubble modes of the contrast to the energy density when evaluated in e.g. the synchronous gauge
Small paragraph style, for those modes smaller than the Jeans length the evolution cannot bring the small perturbations in the early universe to the nonlinear regime, and the inhomogeneities are erased. This will introduce a cutoff in the mass power spectrum for the distribution of galaxies in the universe. Something similar happens in warm DM scenarios [15].
For a canonical scalar field we have c 2 s = 1, see e.g. Ref. [3], and it is usually argued that this implies that small perturbations in the energy density do not grow [4]. This would seem to be a very serious argument against the whole scalar field DM program.
One should also mention that recently the problem of structure formation with a massive scalar field has been studied by performing full nonlinear numerical simulations of the EinsteinKlein-Gordon system, both in the relativistic [9] and the nonrelativistic [10] regimes. However, we believe that by studying the problem from the point of view of a mode analysis in perturbation theory one can more clearly separate the relevant physical mechanisms that come into play at different scales.
At very large scales the universe is (nearly) homogeneous and isotropic; that makes it possible to introduce the idea of a homogeneous and isotropic background. According to the current cosmological observations this background can be described in terms of a flat RobertsonWalker (RW) metric of the form…