119098145
Behavior of f(R) gravity in the solar system, galaxies, and clusters
For cosmologically interesting f(R) gravity models, we derive the complete set of the linearized field equations in the Newtonian gauge, under environments of the solar system, galaxies, and clusters, respectively. Based on these equations, we confirm the previous gamma=1/2 solution in the solar system. However, f(R) gravity models can be strongly environment dependent and the high density (comparing to the cosmological mean) solar system environment can excite a viable gamma=1 solution for some f(R) gravity models. Although for f(R)proportional to-1/R, it is not the case; for f(R)proportional to-exp(-R/lambda H-2(0)2), such a gamma=1 solution does exist. This solution is virtually indistinguishable from that in general relativity (GR) and the value of the associated curvature approaches the GR limit, which is much higher than the value in the gamma=1/2 solution. We show that for some forms of f(R) gravity, this solution is physically stable in the solar system and can smoothly connect to the surface of the Sun. The derived field equations can be applied directly to gravitational lensing of galaxies and clusters. We find that, despite a significant difference in the environments of galaxies and clusters comparing to that of the solar system, gravitational lensing of galaxies and clusters can be virtually identical to that in GR, for some forms of f(R) gravity. Fortunately, galaxy rotation curve and intracluster gas pressure profile may contain valuable information to distinguish these f(R) gravity models from GR.
16130045
Isolating the Decay Rate of Cosmological Gravitational Potential
The decay rate of cosmological gravitational potential measures the deviation from Einstein-de Sitter universe and can put strong constraints on the nature of dark energy and gravity. The usual method to measure this decay rate is through the integrated Sachs-Wolfe (ISW) effect-large-scale structure (LSS) cross-correlation. However, the interpretation of the measured correlation signal is complicated by galaxy bias and the matter power spectrum. This could bias and/or degrade its constraints on the nature of dark energy and gravity. But combining the lensing-LSS cross-correlation measurements, the decay rate of gravitational potential can be isolated. For any given narrow redshift bin of LSS, the ratio of the two cross-correlations directly measures H(z)/W(χ, χs), where D is the linear growth factor of the gravitational potential, H is the Hubble constant at redshift z, W(χ, χs) is the lensing kernel, and χ and χs are the comoving angular diameter distance to lens and source, respectively. This method is optimal in the sense that (1) the measured quantity is essentially free of systematic errors and is only limited by cosmic variance, and (2) the measured quantity depends only on several cosmological parameters and can be predicted from first principles unambiguously. Although fundamentally limited by the inevitably large cosmic variance associated with the ISW measurements, it can still put useful independent constraints on the amount of dark energy and its equation of state. It can also provide a powerful test of modified gravity and can distinguish the Dvali-Gabadadze-Porrati model from ΛCDM at >2.5 σ confidence level.
119091401
The dark flow induced small-scale kinetic Sunyaev–Zel'dovich effect
Recently, Kashlinsky et al. reported a discovery of a similar to 10(3) km s(-1) bulk flow of the Universe out to z similar or equal to 0.3, through the dark flow induced cosmic microwave background (CMB) dipole in directions of clusters. We point out that, if this dark flow exists, it will also induce observable CMB temperature fluctuations at multipole l similar to 10(3), through modulation of the inhomogeneous electron distribution on the uniform dark flow. The induced small-scale kinetic Sunyaev-Zel'dovich (SZ) effect will reach similar to 1 mu K-2 at multipole 10(3) less than or similar to l less than or similar to 10(4), only a factor of similar to 2 smaller than the conventional kinetic SZ effect. Furthermore, it will be correlated with the large-scale structure (LSS) and its correlation with Two-Micron All-Sky Survey (2MASS) galaxy distribution reaches 0.3 mu K at l = 10(3), under a directional dependent optimal weighting scheme. We estimate that, Wilkinson Microwave Anisotropy Probe plus 2MASS should already be able to detect this dark flow induced small-scale kinetic SZ effect with similar to 6 sigma confidence. Deeper galaxy surveys such as the Sloan Digital Sky Survey can further improve the measurement. Planck plus existing galaxy surveys can reach greater than or similar to 14 sigma detection. Existing CMB-LSS cross-correlation measurements shall be reanalysed to test the existence of the dark flow and, if it exists, shall be used to eliminate possible bias on the integrated Sachs-Wolfe effect measurement through the CMB-LSS cross-correlation.
15003877
SELF-CALIBRATION OF GRAVITATIONAL SHEAR-GALAXY INTRINSIC ELLIPTICITY CORRELATION IN WEAK LENSING SURVEYS
The galaxy intrinsic alignment is a severe challenge to precision cosmic shear measurement. We propose self-calibrating the induced gravitational shear-galaxy intrinsic ellipticity correlation (the GI correlation) in weak lensing surveys with photometric redshift measurements. (1) We propose a method to extract the intrinsic ellipticity-galaxy density cross-correlation (I-g) from the galaxy ellipticity-density measurement in the same redshift bin. (2) We also find a generic scaling relation to convert the extracted I-g correlation to the necessary GI correlation. We perform a concept study under simplified conditions and demonstrate its capability to significantly reduce GI contamination. We discuss the impact of various complexities on the two key ingredients of the self-calibration technique, namely the method for extracting the I-g correlation and the scaling relation between the I-g and the GI correlation. We expect that none of them will likely be able to completely invalidate the proposed self-calibration technique.
14253775
SELF CALIBRATION OF GALAXY BIAS IN SPECTROSCOPIC REDSHIFT SURVEYS OF BARYON ACOUSTIC OSCILLATIONS
Baryon acousticoscillation (BAO)isapowerfulprobeon theexpansion oftheuniverse,sheddinglight on elusive dark energy and gravity atcosm ologicalscales. BAO m easurem entsthrough biased trac- ersofthe underlying m atterdensityeld,asm ostproposalsdo,can reach high statisticalaccuracy. However,possible scale dependence in biasm ay induce non-negligiblesystem aticalerrors,especially forthem ostam bitiousspectroscopicsurveysproposed.W eshow thatprecision spectroscopicredshift inform ation availablein thesesurveysallowsfor selfcalibration ofthegalaxybiasand itsstochasticity, as function ofscale and redshift. Through the eect ofredshift distortion,one can sim ultaneously m easure the realspace powerspectra ofgalaxies,galaxy-velocity and velocity,respectively. Atrel- evantscalesofBAO,galaxy velocity faithfully tracesthatofthe underlying m atter. This valuable feature enablesa ratherm odelindependentway to m easure the galaxy biasand itsstochasticity by com paring the three power spectra. For the square kilom eter array (SKA),this selfcalibration is statistically accurateto correctfor1% levelshiftin BAO peak positionsinduced by biasscaledepen- dence.Furtherm ore,wend thatSKA isabletodetectBAO in thevelocity powerspectrum ,opening a new window forBAO cosm ology. Subjectheadings: cosm ology:distancescale{large-scalestructureofuniverse{theory 1. IN TRO D U CTIO N
15276899
The effect of cluster magnetic field on the Sunyaev–Zel'dovich power spectrum
Precision measurements of the Sunyaev–Zel'dovich (SZ) effect in upcoming blank sky surveys require theoretical understanding of all physical processes with ≳10 per cent effects on the SZ power spectrum. We show that the observed cluster magnetic field could reduce the SZ power spectrum by ∼20 per cent at l∼ 4000, where the SZ power spectrum will be precisely measured by the Sunyaev–Zel'dovich array (SZA) and the Atacama Cosmology Telescope (ACT). At smaller scale, this effect is larger and could reach a factor of several. Such an effect must be considered for an unbiased interpretation of the SZ data. Although the magnetic effect on the SZ power spectrum is very similar to that of radiative cooling, it is measurable by multiband cosmic microwave background polarization measurement.
6475881
Energy-Momentum of a Cosmological Brane Model and the Gauge Hierarchy
We analyze in this paper the general covariant energy-momentum tensor of the gravitational system in general five-dimensional cosmological brane-world models. Then through calculating this energy-momentum for the cosmological generalization of the Randall-Sundrum model, which includes the original RS model as the static limit, we are able to show that the weakness of the gravitation on the “visible” brane is a general feature of this model. This is the origin of the gauge hierarchy from a gravitational point of view. Our results are also consistent with the fact that a gravitational system has vanishing total energy.
44301996
BEAM-BASED HOM STUDY IN THIRD HARMONIC SC CAVITIES FOR BEAM ALIGNMENT AT FLASH*
An electron beam entering an accelerator cavity excites higher order modes (HOM). These are radiated to HOM couplers and subsequently damped. They can also be used to facilitate beam position monitoring. The modes excited by off-axis beams are the focus of this study. Results are presented on the first analysis of HOM dependency on the beam position for the third harmonic cavities at FLASH. The analysis is based on the beampipe and cavity dipole modes. Various analysis methods are used and compared to satisfy the needs emerging from the characteristics of those modes. The electric center of each mode is observed by looking for the minima of the HOM signals of different beam positions. A single electron bunch per RF pulse is used.
119117894
The generalized second law of thermodynamics in generalized gravity theories
We investigate the generalized second law of thermodynamics (GSL) in generalized theories of gravity. We examine the total entropy evolution with time including the horizon entropy, the non-equilibrium entropy production, and the entropy of all matter, field and energy components. We derive a universal condition to protect the generalized second law and study its validity in different gravity theories. In Einstein gravity (even in the phantom-dominated universe with a Schwarzschild black hole), Lovelock gravity and braneworld gravity, we show that the condition to keep the GSL can always be satisfied. In f(R) gravity and scalar?tensor gravity, the condition to protect the GSL can also hold because the temperature should be positive, gravity is always attractive and the effective Newton constant should be an approximate constant satisfying the experimental bounds.
32996904
Higher order modes in third harmonic cavities for XFEL/FLASH
We analyse higher order modes in the 3.9 GHz bunch shaping cavities recently installed in the FLASH facility at DESY. We report on recent experimental results on the frequency spectrum from probe based measurements made at CMTB at DESY. These are compared to those predicted by finite difference and finite element computer codes. This study is focused mainly on the dipole component of the multi-pole expansion of the wakefield. The modes are readily identifiable as single-cavity modes provided the frequencies of these modes are below the cut-off of the inter-connecting beam pipes. The modes above cut-off are coupled to the 4 cavities and are distinct from single cavity modes.
118309815
Kohn's theorem and Galilean symmetry
Abstract The relation between the separability of a system of charged particles in a uniform magnetic field and Galilean symmetry is revisited using Duvalʼs “Bargmann framework”. If the charge-to-mass ratios of the particles are identical, e a / m a = ϵ for all particles, then the Bargmann space of the magnetic system is isometric to that of an anisotropic harmonic oscillator. Assuming that the particles interact through a potential which only depends on their relative distances, the system splits into one representing the center of mass plus a decoupled internal part, and can be mapped further into an isolated system using Niedererʼs transformation. Conversely, the manifest Galilean boost symmetry of the isolated system can be “imported” to the oscillator and to the magnetic systems, respectively, to yield the symmetry used by Gibbons and Pope to prove the separability. For vanishing interaction potential the isolated system is free and our procedure endows all our systems with a hidden Schrodinger symmetry, augmented with independent internal rotations. All these properties follow from the cohomological structure of the Galilei group, as explained by Souriauʼs “decomposition barycentrique” .