39 research outputs found
On The Halo-Mass And Radial Scale Dependence Of The Lensing Is Low Effect
The canonical Lambda cold dark matter (ÎCDM) cosmological model makes precise predictions for the clustering and lensing properties of galaxies. It has been shown that the lensing amplitude of galaxies in the Baryon Oscillation Spectroscopic Survey (BOSS) is lower than expected given their clustering properties. We present new measurements and modelling of galaxies in the BOSS LOWZ sample. We focus on the radial and stellar mass dependence of the lensing amplitude mismatch. We find an amplitude mismatch of around 35 per cent when assuming ÎCDM with Planck Cosmological Microwave Background (CMB) constraints. This offset is independent of halo mass and radial scale in the range Mhalo ⌠1013.3â1013.9hâ1 Mâ and r=0.1â60hâ1Mpc (â kâ0.05â20hMpcâ1â ). The observation that the offset is both mass and scale independent places important constraints on the degree to which astrophysical processes (baryonic effects, assembly bias) can fully explain the effect. This scale independence also suggests that the âlensing is lowâ effect on small and large radial scales probably have the same physical origin. Resolutions based on new physics require a nearly uniform suppression, relative to ÎCDM predictions, of the amplitude of matter fluctuations on these scales. The possible causes of this are tightly constrained by measurements of the CMB and of the low-redshift expansion history
Cosmic Ray Spectra in Nambu-Goldstone Dark Matter Models
We discuss the cosmic ray spectra in annihilating/decaying Nambu-Goldstone
dark matter models. The recent observed positron/electron excesses at PAMELA
and Fermi experiments are well fitted by the dark matter with a mass of 3TeV
for the annihilating model, while with a mass of 6 TeV for the decaying model.
We also show that the Nambu-Goldstone dark matter models predict a distinctive
gamma-ray spectrum in a certain parameter space.Comment: 16 pages, 4 figure
Dark energy with gravitational lens time delays
Strong lensing gravitational time delays are a powerful and cost effective
probe of dark energy. Recent studies have shown that a single lens can provide
a distance measurement with 6-7 % accuracy (including random and systematic
uncertainties), provided sufficient data are available to determine the time
delay and reconstruct the gravitational potential of the deflector.
Gravitational-time delays are a low redshift (z~0-2) probe and thus allow one
to break degeneracies in the interpretation of data from higher-redshift probes
like the cosmic microwave background in terms of the dark energy equation of
state. Current studies are limited by the size of the sample of known lensed
quasars, but this situation is about to change. Even in this decade, wide field
imaging surveys are likely to discover thousands of lensed quasars, enabling
the targeted study of ~100 of these systems and resulting in substantial gains
in the dark energy figure of merit. In the next decade, a further order of
magnitude improvement will be possible with the 10000 systems expected to be
detected and measured with LSST and Euclid. To fully exploit these gains, we
identify three priorities. First, support for the development of software
required for the analysis of the data. Second, in this decade, small robotic
telescopes (1-4m in diameter) dedicated to monitoring of lensed quasars will
transform the field by delivering accurate time delays for ~100 systems. Third,
in the 2020's, LSST will deliver 1000's of time delays; the bottleneck will
instead be the aquisition and analysis of high resolution imaging follow-up.
Thus, the top priority for the next decade is to support fast high resolution
imaging capabilities, such as those enabled by the James Webb Space Telescope
and next generation adaptive optics systems on large ground based telescopes.Comment: White paper submitted to SNOWMASS201
Absolute electron and positron fluxes from PAMELA/Fermi and Dark Matter
We extract the positron and electron fluxes in the energy range 10 - 100 GeV
by combining the recent data from PAMELA and Fermi LAT. The {\it absolute
positron and electron} fluxes thus obtained are found to obey the power laws:
and respectively, which can be confirmed by the
upcoming data from PAMELA. The positron flux appears to indicate an excess at
energies E\gsim 50 GeV even if the uncertainty in the secondary positron flux
is added to the Galactic positron background. This leaves enough motivation for
considering new physics, such as annihilation or decay of dark matter, as the
origin of positron excess in the cosmic rays.Comment: Accepted by JCA
Neutrino Self-Interactions: A White Paper
Neutrinos are the Standard Model (SM) particles which we understand theleast, often due to how weakly they interact with the other SM particles.Beyond this, very little is known about interactions among the neutrinos, i.e.,their self-interactions. The SM predicts neutrino self-interactions at a levelbeyond any current experimental capabilities, leaving open the possibility forbeyond-the-SM interactions across many energy scales. In this white paper, wereview the current knowledge of neutrino self-interactions from a vast array ofprobes, from cosmology, to astrophysics, to the laboratory. We also discusstheoretical motivations for such self-interactions, including neutrino massesand possible connections to dark matter. Looking forward, we discuss thecapabilities of searches in the next generation and beyond, highlighting thepossibility of future discovery of this beyond-the-SM physics.<br
Extragalactic Inverse Compton Light from Dark Matter Annihilation and the Pamela Positron Excess
We calculate the extragalactic diffuse emission originating from the
up-scattering of cosmic microwave photons by energetic electrons and positrons
produced in particle dark matter annihilation events at all redshifts and in
all halos. We outline the observational constraints on this emission and we
study its dependence on both the particle dark matter model (including the
particle mass and its dominant annihilation final state) and on assumptions on
structure formation and on the density profile of halos. We find that for
low-mass dark matter models, data in the X-ray band provide the most stringent
constraints, while the gamma-ray energy range probes models featuring large
masses and pair-annihilation rates, and a hard spectrum for the injected
electrons and positrons. Specifically, we point out that the all-redshift,
all-halo inverse Compton emission from many dark matter models that might
provide an explanation to the anomalous positron fraction measured by the
Pamela payload severely overproduces the observed extragalactic gamma-ray
background.Comment: Version accepted for publication in JCAP, one new figure and text
added; 19 pages, 5 figure
Snowmass2021 - Letter of interest cosmology intertwined IV: the age of the universe and its curvature
A precise measurement of the curvature of the Universe is of prime importance for cosmology since it could not only confirm the paradigm of primordial inflation but also help in discriminating between different early-Universe scenarios. Recent observations, while broadly consistent with a spatially flat standard Cold Dark Matter (CDM) model, show tensions that still allow (and, in some cases, even suggest) a few percent deviations from a flat universe. In particular, the Planck Cosmic Microwave Background power spectra, assuming the nominal likelihood, prefer a closed universe at more than 99% confidence level. While new physics could be at play, this anomaly may be the result of an unresolved systematic error or just a statistical fluctuation. However, since positive curvature allows a larger age of the Universe, an accurate determination of the age of the oldest objects provides a smoking gun in confirming or falsifying the current flat CDM model
Snowmass2021 - Letter of interest cosmology intertwined I: Perspectives for the next decade
The standard Cold Dark Matter cosmological model provides an amazing description of a wide range of astrophysical and astronomical data. However, there are a few big open questions, that make the standard model look like a first-order approximation to a more realistic scenario that still needs to be fully understood. In this Letter of Interest we will list a few important goals that need to be addressed in the next decade, also taking into account the current discordances present between the different cosmological probes, as the Hubble constant value, the tension, and the anomalies present in the Planck results. Finally, we will give an overview of upgraded experiments and next-generation space-missions and facilities on Earth that will be of crucial importance to address all these questions
Cosmology intertwined III: fÏ8 and S8
The standard Cold Dark Matter cosmological model provides a wonderful fit to current cosmological data, but a few statistically significant tensions and anomalies were found in the latest data analyses. While these anomalies could be due to the presence of systematic errors in the experiments, they could also indicate the need for new physics beyond the standard model. In this Letter of Interest we focus on the tension between Planck data and weak lensing measurements and redshift surveys, in the value of the matter energy density and the amplitude (or the growth rate ) of cosmic structure. We list a few promising models for solving this tension, and discuss the importance of trying to fit multiple cosmological datasets with complete physical models, rather than fitting individual datasets with a few handpicked theoretical parameters
Snowmass2021 - Letter of interest cosmology intertwined II: the hubble constant tension
The current cosmological probes have provided a fantastic confirmation of the standard Cold Dark Matter cosmological model, which has been constrained with unprecedented accuracy. However, with the increase of the experimental sensitivity, a few statistically significant tensions between different independent cosmological datasets emerged. While these tensions can be in part the result of systematic errors, the persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the need for new physics. In this Letter of Interest we will focus on the tension between the Planck estimate of the Hubble constant and the SH0ES collaboration measurements. After showing the evaluations made from different teams using different methods and geometric calibrations, we will list a few interesting models of new physics that could solve this tension and discuss how the next decadeâs experiments will be crucial