37,320 research outputs found
Characterizing the Epoch of Reionization with the small-scale CMB: constraints on the optical depth and physical parameters
Patchy reionization leaves a number of imprints on the small-scale cosmic
microwave background (CMB) temperature fluctuations, the largest of which is
the kinematic Sunyaev-Zel'dovich (kSZ), the Doppler shift of CMB photons
scattering off moving electrons in ionized bubbles. It has long been known that
in the CMB power spectrum, this imprint of reionization is largely degenerate
with the kSZ signal produced by late-time galaxies and clusters, thus limiting
our ability to constrain reionization. Following Smith & Ferraro (2017), it is
possible to isolate the reionization contribution in a model independent way,
by looking at the large scale modulation of the small scale CMB power spectrum.
In this paper we extend the formalism to use the full shape information of the
small scale power spectrum (rather than just its broadband average), and argue
that this is necessary to break the degeneracy between the optical depth
and parameters setting the duration of reionization. In particular, we show
that the next generation of CMB experiments could achieve up to a factor of 3
improvement on the optical depth and at the same time, constrain the
duration of reionization to 25 %. This can help tighten the constrains
on neutrino masses, which will be limited by our knowledge of , and shed
light on the physical processes responsible for reionization.Comment: 8 pages, 3 figures. Comments welcom
Detecting patchy reionization in the CMB
Upcoming cosmic microwave background (CMB) experiments will measure
temperature fluctuations on small angular scales with unprecedented precision.
Small-scale CMB fluctuations are a mixture of late-time effects: gravitational
lensing, Doppler shifting of CMB photons by moving electrons (the kSZ effect),
and residual foregrounds. We propose a new statistic which separates the kSZ
signal from the others, and also allows the kSZ signal to be decomposed in
redshift bins. The decomposition extends to high redshift, and does not require
external datasets such as galaxy surveys. In particular, the high-redshift
signal from patchy reionization can be cleanly isolated, enabling future CMB
experiments to make high-significance and qualitatively new measurements of the
reionization era
The influence of lifelong learning on mood
Mood state was assessed both before and after four different two-hour classes in the Osher Lifelong Learning Institute at Santa Clara University with the self-report Profile of Mood States-Brief Form (POMS-BF) developed by McNair, Lorr, and Droppleman (1992). Sixty-eight students (60% women), ages 49 to 92, filled in the 5-point mood assessment survey rating how they felt at that moment prior to the start of class and again two hours later, at the end of class. At the start of class these students reported very low levels of negative affect (tension, anger, depression, confusion, fatigue). Following the two-hour Osher class students felt even less angry, less tense, and less depressed than they were before the class. These results are discussed in relation to mood regulation and the detrimental impact of negative affect on cognition (e.g., Wilson, Mendes de Leon, Bennett, Bienias, Evans, 2004)
Supersonic baryon-CDM velocities and CMB B-mode polarization
It has recently been shown that supersonic relative velocities between dark
matter and baryonic matter can have a significant effect on formation of the
first structures in the universe. If this effect is still non-negligible during
the epoch of hydrogen reionization, it generates large-scale anisotropy in the
free electron density, which gives rise to a CMB B-mode. We compute the B-mode
power spectrum and find a characteristic shape with acoustic peaks at l ~ 200,
400, ... The amplitude of this signal is a free parameter which is related to
the dependence of the ionization fraction on the relative baryon-CDM velocity
during the epoch of reionization. However, we find that the B-mode signal is
undetectably small for currently favored reionization models in which hydrogen
is reionized promptly at z ~ 10, although constraints on this signal by future
experiments may help constrain models in which partial reionization occurs at
higher redshift, e.g. by accretion onto primordial black holes.Comment: 5 pages, 3 figure
Least costly energy management for series hybrid electric vehicles
Energy management of plug-in Hybrid Electric Vehicles (HEVs) has different
challenges from non-plug-in HEVs, due to bigger batteries and grid recharging.
Instead of tackling it to pursue energetic efficiency, an approach minimizing
the driving cost incurred by the user - the combined costs of fuel, grid energy
and battery degradation - is here proposed. A real-time approximation of the
resulting optimal policy is then provided, as well as some analytic insight
into its dependence on the system parameters. The advantages of the proposed
formulation and the effectiveness of the real-time strategy are shown by means
of a thorough simulation campaign
On the scatter in the relation between stellar mass and halo mass: random or halo formation time dependent?
The empirical HOD model of Wang et al. 2006 fits, by construction, both the
stellar mass function and correlation function of galaxies in the local
Universe. In contrast, the semi-analytical models of De Lucia & Blazoit 2007
(DLB07) and Guo et al. 2011 (Guo11), built on the same dark matter halo merger
trees than the empirical model, still have difficulties in reproducing these
observational data simultaneously. We compare the relations between the stellar
mass of galaxies and their host halo mass in the three models, and find that
they are different. When the relations are rescaled to have the same median
values and the same scatter as in Wang et al., the rescaled DLB07 model can fit
both the measured galaxy stellar mass function and the correlation function
measured in different galaxy stellar mass bins. In contrast, the rescaled Guo11
model still over-predicts the clustering of low-mass galaxies. This indicates
that the detail of how galaxies populate the scatter in the stellar mass --
halo mass relation does play an important role in determining the correlation
functions of galaxies. While the stellar mass of galaxies in the Wang et al.
model depends only on halo mass and is randomly distributed within the scatter,
galaxy stellar mass depends also on the halo formation time in semi-analytical
models. At fixed value of infall mass, galaxies that lie above the median
stellar mass -- halo mass relation reside in haloes that formed earlier, while
galaxies that lie below the median relation reside in haloes that formed later.
This effect is much stronger in Guo11 than in DLB07, which explains the
over-clustering of low mass galaxies in Guo11. Our results illustrate that the
assumption of random scatter in the relation between stellar and halo mass as
employed by current HOD and abundance matching models may be problematic in
case a significant assembly bias exists in the real Universe.Comment: 10 pages, 6 figures, published in MNRA
- …