Search results for "Cosmology and Extragalactic Astrophysics"
showing 10 items of 1668 documents
Coupled dark matter-dark energy in light of near Universe observations
2010
Cosmological analysis based on currently available observations are unable to rule out a sizeable coupling among the dark energy and dark matter fluids. We explore a variety of coupled dark matter-dark energy models, which satisfy cosmic microwave background constraints, in light of low redshift and near universe observations. We illustrate the phenomenology of different classes of dark coupling models, paying particular attention in distinguishing between effects that appear only on the expansion history and those that appear in the growth of structure. We find that while a broad class of dark coupling models are effectively models where general relativity (GR) is modified - and thus can b…
Looking for MACHOs in the Spectra of Fast Radio Bursts
2019
We explore a novel search strategy for dark matter in the form of massive compact halo objects (MACHOs) such as primordial black holes or dense mini-halos in the mass range from $10^{-4}$ to 0.1 solar masses. These objects can gravitationally lens the signal of fast radio bursts (FRBs), producing a characteristic interference pattern in the frequency spectrum, similar to the previously studied femtolensing signal in gamma ray burst spectra. Unlike traditional searches using microlensing, FRB lensing will probe the abundance of MACHOs at cosmological distance scales (~Gpc) rather than just their distribution in the neighborhood of the Milky Way. The method is thus particularly relevant for d…
PBH assisted search for QCD axion dark matter
2022
The entropy production prior to BBN era is one of ways to prevent QCD axion with the decay constant $F_{a}\in[10^{12}{\rm GeV},10^{16}{\rm GeV}]$ from overclosing the universe when the misalignment angle is $\theta_{\rm i}=\mathcal{O}(1)$. As such, it is necessarily accompanied by an early matter-dominated era (EMD) provided the entropy production is achieved via the decay of a heavy particle. In this work, we consider the possibility of formation of primordial black holes during the EMD era with the assumption of the enhanced primordial scalar perturbation on small scales ($k>10^{4}{\rm Mpc}^{-1}$). In such a scenario, it is expected that PBHs with axion halo accretion develop to ultracomp…
Dark Sectors and New, Light, Weakly-Coupled Particles
2013
Dark sectors, consisting of new, light, weakly-coupled particles that do not interact with the known strong, weak, or electromagnetic forces, are a particularly compelling possibility for new physics. Nature may contain numerous dark sectors, each with their own beautiful structure, distinct particles, and forces. This review summarizes the physics motivation for dark sectors and the exciting opportunities for experimental exploration. It is the summary of the Intensity Frontier subgroup "New, Light, Weakly-coupled Particles" of the Community Summer Study 2013 (Snowmass). We discuss axions, which solve the strong CP problem and are an excellent dark matter candidate, and their generalizatio…
Femtolensing by dark matter revisited
2018
Femtolensing of gamma ray bursts (GRBs) has been put forward as an exciting possibility to probe exotic astrophysical objects with masses below $10^{-13}$ solar masses such as small primordial black holes or ultra-compact dark matter minihalos, made up for instance of QCD axions. In this paper we critically review this idea, properly taking into account the extended nature of the source as well as wave optics effects. We demonstrate that most GRBs are inappropriate for femtolensing searches due to their large sizes. This removes the previous femtolensing bounds on primordial black holes, implying that vast regions of parameter space for primordial black hole dark matter are not robustly con…
Search for GW signals associated with GRBs
2021
We present the results of targeted searches for gravitational-wave transients associated with gamma-ray bursts during the second observing run of Advanced LIGO and Advanced Virgo, which took place from 2016 November to 2017 August. We have analyzed 98 gamma-ray bursts using an unmodeled search method that searches for generic transient gravitational waves and 42 with a modeled search method that targets compact-binary mergers as progenitors of short gamma-ray bursts. Both methods clearly detect the previously reported binary merger signal GW170817, with p-values of <9.38x10^-6^ (modeled) and 3.1x10^-4^ (unmodeled). We do not find any significant evidence for gravitational-wave signals assoc…
Nebular emission lines towards NGC3372 center
2016
We present observations from the Gaia-ESO Survey in the lines of H{alpha}, [NII], [SII], and He I of nebular emission in the central part of the Carina nebula. We investigate the properties of the two already known kinematic components (approaching and receding), which account for the bulk of emission. Moreover, we investigate the features of the much less known low-intensity high-velocity (absolute RV>50km/s) gas emission. We show that gas giving rise to H{alpha} and HeI emission is dynamically well correlated with but not identical to gas seen through forbidden-line emission. Gas temperatures are derived from line-width ratios, and densities from [SII] doublet ratios. The spatial variatio…
Cosmological lepton asymmetry with a nonzero mixing angle \theta13
2012
While the baryon asymmetry of the Universe is nowadays well measured by cosmological observations, the bounds on the lepton asymmetry in the form of neutrinos are still significantly weaker. We place limits on the relic neutrino asymmetries using some of the latest cosmological data, taking into account the effect of flavor oscillations. We present our results for two different values of the neutrino mixing angle \theta_{13}, and show that for large \theta_{13} the limits on the total neutrino asymmetry become more stringent, diluting even large initial flavor asymmetries. In particular, we find that the present bounds are still dominated by the limits coming from Big Bang Nucleosynthesis, …
Infrated photometry of NGC 1893
2008
The independence of the star formation processes with respect to the environmental conditions is controversial. In particular it is not clear whether star formation in the outer Galaxy, where the environmental conditions are, theoretically, less conducive, occurs in the same way as in the inner Galaxy. We investigate the population of NGC 1893, a young cluster (~3-4Myr) in the outer part of the Galaxy (galactic radius >11kpc) in order to explore the effects of environmental conditions on star forming regions. We present the infrared observations obtained with the IRAC camera on board of the Spitzer Space Telescope and analyze the color-color diagrams to establish the membership of stars wit…
Old MS stars in young moving groups
2009
The associations and moving groups of young stars are excellent laboratories to investigate the stellar formation in the solar neighborhood. Past results confirmed that a non-negligible fraction of old main-sequence stars is present in the lists of members of the young stellar kinematic groups. A detailed study on the properties of these samples is needed to separate the young stars from old main-sequence stars with similar space motion, in order to identify the origin of these structures. Our intention is to characterize the sample of stars members of the young moving groups and determine their age distribution to quantify the contamination by old main-sequence stars, in particular, in the…