119269042
Exploring the origin of the fine structures in the CMB temperature angular power spectrum
The angular power spectrum of the cosmic microwave background (CMB) temperature anisotropies is a good probe to look into the primordial density fluctuations at large scales in the universe. Here we re-examine the angular power spectrum of the Wilkinson Microwave Anisotropy Probe data, paying particular attention to the fine structures (oscillations) at $\ell=100 \sim 150$ reported by several authors. Using Monte-Carlo simulations, we confirm that the gap from the simple power law spectrum is a rare event, about 2.5--3$\sigma$, if these fine structures are generated by experimental noise and the cosmic variance. Next, in order to investigate the origin of the structures, we examine frequency and direction dependencies of the fine structures by dividing the observed QUV frequency maps into four sky regions. We find that the structures around $\ell \sim 120$ do not have significant dependences either on frequencies or directions. For the structure around $\ell \sim 140$, however, we find that the characteristic signature found in the all sky power spectrum is attributed to the anomaly only in the South East region.
75530
Cosmological constraints from the cluster contribution to the power spectrum of the soft X‐ray background. New evidence for a low σ8?
We use the X-ray power spectrum of the soft X-ray background ROSAT all-sky survey in the R6 band (0.9-1.3 keV) to set an upper limit on the galaxy cluster power spectrum. The cluster power spectrum is modelled with a minimum number of robust assumptions regarding the structure of the clusters. The power spectrum of ROSAT sets an upper limit on the Ω m -σ 8 plane that excludes all the models with σ 8 above σ 8 = 0.5 ′ 0 . 0 8 0.05 Ω - ( 0 . 3 8 ′ 0 . 0 1 0.05) m in a flat A-cold dark matter universe. We discuss the possible sources of systematic errors in our conclusions. mainly dominated by the assumed L x -T relation and some cluster signal subtracted during the point source removal. The uncertainties due to removed clusters can move our upper limit as much as 0.2 units upwards. The systematic bias introduced by uncertainties in the scaling relations is more difficult to quantify since these relations are not accurately known yet but we show how, alternatively, the L x -T relation could be constrained using the X-ray power spectrum, if the cosmological model is known and provided a good estimate of the power spectrum of the diffuse X-ray background can be obtained from the data. Roughly accounting for all the systematics, our conclusions suggest that models with a low value of σ 8 are favoured by the soft X-ray diffuse background. The approach presented in this work would be extremely powerful with high-quality data from Chandra and XMM with a better point source subtraction and going to smaller scales than those proved in this work.
118743945
Solar Neutrino Physics: Sensitivity to Light Dark Matter Particles
Neutrinos are produced in several neutrino nuclear reactions of the proton–proton chain and carbon– nitrogen–oxygen cycle that take place at different radius of the Sun’s core. Hence, measurements of solar neutrino fluxes provide a precise determination of the local temperature. The accumulation of non-annihilating light dark matter particles (with masses between 5 GeV and 16 GeV) in the Sun produces a change in the local solar structure, namely, a decrease in the central temperature of a few percent. This variation depends on the properties of the dark matter particles, such as the mass of the particle and its spin-independent scattering cross-section on baryon-nuclei, specifically, the scattering with helium, oxygen, and nitrogen among other heavy elements. This temperature effect can be measured in almost all solar neutrino fluxes. In particular, by comparing the neutrino fluxes generated by stellar models with current observations, namely 8 B neutrino fluxes, we find that non-annihilating dark matter particles with a mass smaller than 10 GeV and a spin-independent scattering cross-section with heavy baryon-nuclei larger than 3 × 10 −37 cm −2 produce a variation in the 8 B neutrino fluxes that would be in conflict with current measurements.
14905165
Gravitational magnification of the cosmic microwave background
Some aspects of gravitational lensing by large-scale structure are investigated. We show that lensing causes the damping tail of the cosmic microwave background (CMB) power spectrum to fall less rapidly with decreasing angular scale than previously expected. This is because of a transfer of power from larger to smaller angular scales, which produces a fractional change in power spectrum that increases rapidly beyond l~2000. We also find that lensing produces a nonzero mean magnification of structures on surfaces of constant redshift if weighted by area on the sky. This is a result of the fact that light rays that are evenly distributed on the sky oversample overdense regions. However, this mean magnification has a negligible affect on the CMB power spectrum. A new expression for the lensed power spectrum is derived, and it is found that future precision observations of the high-l tail of the power spectrum will need to take lensing into account when determining cosmological parameters.
17129713
Star Formation in Viscous Galaxy Disks
The Lin and Pringle model (1987) of galactic disk formation postulates that if star formation proceeds on the same timescale as the viscous redistribution of mass and angular momentum in disk galaxies, then the stars attain an exponential density profile. Their claim is that this result holds generally: regardless of the disk galaxy's initial gas and dark matter distribution and independent of the nature of the viscous processes acting in the disk. We present new results from a set of 2D hydro-simulations which investigate their analytic result.
120508431
Origin and evolution of the large-scale structure of the universe
Ever since the epoch of the spontaneous breaking of grand unification symmetry between the nuclear and electromagnetic interactions, the universe has expanded under the imprint of a spectrum of density fluctuations that is generally considered to have originated in this phase transition. I will discuss various possibilities for the form of the primordial fluctuation spectrum, spanning the range of adiabatic fluctuations, isocurvature fluctuations, and cosmic strings. Growth of the seed fluctuations by gravitational instability generates the formation of large-scale structures, from the scale of galaxies to that of clusters and superclusters of galaxies. There are three areas of confrontation with observational cosmology that will be reviewed. The large-scale distribution of the galaxies, including the apparent voids, sheets and filaments, and the coherent peculiar velocity field on scales of several tens of megaparsecs, probe the primordial fluctuation spectrum on scales that are only mildly nonlinear. Ev...
122618150
Energy dissipation process for 100-MeV protons and the nucleon-nucleon interactions in nuclei
Coincidence studies of two protons emitted from p+/sup 58/Ni at 100 MeV have been carried out. The proton spectra in coincidence with scattered protons suffering an average energy loss of 60 MeV are similar to those resulting from 60-MeV incident protons. This suggests that the initial interaction of the incident proton is with a bound nucleon and that one or both of these nucleons are emitted or initiates a cascade leading to more complex states.
125435973
Reaction Ni-58 (pi+, p p) at T(pi+) = 160-MeV
119291656
Correlation functions of twist fields from Ward identities in the massive Dirac theory
We derive non-linear differential equations for correlation functions of U(1) twist fields in the two-dimensional massive Dirac theory. Primary U(1) twist fields correspond to exponential fields in the sine-Gordon model at the free-fermion point, and it is well-known that their vacuum two-point functions are determined by integrable differential equations. We extend part of this result to more general quantum states (pure or mixed) and to certain descendents, showing that some two-point functions are determined by the sinh-Gordon differential equations whenever there is translation and parity invariance, and the density matrix is the exponential of a bilinear expression in fermions. We use methods involving Ward identities associated to the copy-rotation symmetry in a model with two independent, anti-commuting copies. Such methods were used in the context of the thermally perturbed Ising quantum field theory model. We show that they are applicable to the Dirac theory as well, and we suggest that they are likely to have a much wider applicability to free fermion models in general. Finally, we note that our form-factor study of descendents twist fields combined with a CFT analysis provides a new way of evaluating vacuum expectation values of primary U(1) twist fields: by deriving and solving a recursion relation.
119268926
More general correlation functions of twist fields from Ward identities in the massive Dirac theory
Following on from previous work we derive the nonlinear differential equations of more general correlators of U(1) twist fields in two-dimensional massive Dirac theory. Using the conserved charges of the double-copy model equations parametrizing the correlators of twist fields with arbitrary twist parameter are found. This method also gives a parametrization of the correlation functions of general, fermionic, descendent twist fields. The equations parametrizing correlators of primary twist fields are compared to those of the literature and evidence is presented to confirm that these equations represent the correct parametrization.