118857369
Constraints on scalar-tensor theories of gravity from observations
In spite of their original discrepancy, both dark energy and modified theory of gravity can be parameterized by the effective equation of state (EOS) ω for the expansion history of the Universe. A useful model independent approach to the EOS of them can be given by so-called Chevallier-Polarski-Linder (CPL) parametrization where two parameters of it (ω0 and ωa) can be constrained by the geometrical observations which suffer from degeneracies between models. The linear growth of large scale structure is usually used to remove these degeneracies. This growth can be described by the growth index parameter γ and it can be parameterized by γ0+γa(1−a) in general. We use the scalar-tensor theories of gravity (STG) and show that the discernment between models is possible only when γa is not negligible. We show that the linear density perturbation of the matter component as a function of redshift severely constrains the viable subclasses of STG in terms of ω and γ. From this method, we can rule out or prove the viable STG in future observations. When we use Z() = 1, F shows the convex shape of evolution in a viable STG model. The viable STG models with Z() = 1 are not distinguishable from dark energy models when we strongly limit the solar system constraint.
117762235
Correct sub-horizon scales linear perturbation equation for general dark energy models
1970563
Can strong gravitational lensing constrain dark energy
We discuss the ratio of the angular diameter distances from the source to the lens, D{sub ds}, and to the observer at present, D{sub s}, for various dark energy models. It is well known that the difference of D{sub s}s between the models is apparent and this quantity is used for the analysis of Type Ia supernovae. However we investigate the difference between the ratio of the angular diameter distances for a cosmological constant, (D{sub ds}/D{sub s}){sup {lambda}}, and that for other dark energy models, (D{sub ds}/D{sub s}){sup other}, in this paper. It has been known that there is lens model degeneracy in using strong gravitational lensing. Thus, we investigate the model independent observable quantity, Einstein radius ({theta}{sub E}), which is proportional to both D{sub ds}/D{sub s} and velocity dispersion squared, {sigma}{sub v}{sup 2}. D{sub ds}/D{sub s} values depend on the parameters of each dark energy model individually. However, (D{sub ds}/D{sub s}){sup {lambda}}-(D{sub ds}/D{sub s}){sup other} for the various dark energy models, is well within the error of {sigma}{sub v} for most of the parameter spaces of the dark energy models. Thus, a single strong gravitational lensing by use of the Einstein radius may not be a proper method tomore » investigate the property of dark energy. However, better understanding to the mass profile of clusters in the future or other methods related to arc statistics rather than the distances may be used for constraints on dark energy.« less
3165699
Growth index in an accelerating universe
We obtain the exact analytic form of growth index ($f = \Omega_{m}(a)^{\gamma}$) at present epoch in a flat universe for the general value of constant equation of state of dark energy $\omega_{de}$. For the cosmological constant ($\omega_{de} = -1$) we obtain $\gamma = 0.5547$ which is very close to the well known value 6/11. However, if $\omega_{de} = -0.9$, then $\gamma$ gives rise to 0.6405. This result is quite different from that of some other literatures. This discrepancy happens because the numerical solution includes not only the growing mode solution but also the decaying one in some literatures. Thus, the numerical estimation of $\delta$ is over estimated in some references. $\Omega_{m}^{0}$ dependence of $\gamma$ is fairly small for the viable range of the current matter energy density $0.2 \leq \Omega_{m}^{0} \leq 0.3$. (0.6% and 3% changes in $\gamma$ for $\omega_{de}$ equal to -1 and -0.9, respectively.) The difference of peculiar velocity values from the different choices of $\gamma$ is about 11% for $\Omega_{m}^{0} = 0.3$. This simple but accurate formula which covers a large class of dark energy models will provide a practical tool for galaxy redshift survey to measure the matter density and the peculiar velocity.
118495217
Evidence for departure from \Lambda CDM with LSS
We investigate the growth index parameter \gamma and the time variation of the gravitational constant G_{eff} by using the currently available growth function f(z) data at different redshifts, with and without scaling to the fiducial \Lambda CDM model. We inquire the four different models of \gamma including a constant \gamma. From a \chi^2 minimization, we constrain the parameter spaces of models and show that \Lambda CDM model is excluded by 1-\sigma level from current f(z) data. G_{eff} is different from the Newton's gravitational constant G_{N} in modified gravity theories and interestingly, the current data shows that G_{eff} \neq G_{N} at z \gtrsim 0.2 \sim 0.3 at 3-\sigma level. From these, we conclude that Einstein's General Relativity with \Lambda CDM is ruled out by 99% confidence level from large scale structure observations.
15011888
Effect on cosmic microwave background polarization of coupling of quintessence to pseudoscalar formed from the electromagnetic field and its dual.
We present the full set of power spectra of cosmic microwave background (CMB) temperature and polarization anisotropies due to the coupling between quintessence and pseudoscalar of electromagnetism. This coupling induces a rotation of the polarization plane of the CMB, thus resulting in a nonvanishing B mode and parity-violating TB and EB modes. Using the BOOMERANG data from the flight of 2003, we derive the most stringent constraint on the coupling strength. We find that in some cases the rotation-induced B mode can confuse the hunting for the gravitational lensing-induced B mode.
119501262
EMERGENCE OF GRAVITY FROM INTERACTING SIMPLICES
We consider a statistical model of interacting 4-simplices fluctuating in an N-dimensional target space. We argue that a gravitational theory may arise as a low energy effective theory in a strongly interacting phase where the simplices form clusters with an emergent space and time with the Euclidean signature. In the large N limit, two possible phases are discussed, that is, "gravitational Coulomb phase" and "gravitational Higgs phase."
17587151
Nuclear Density-Dependent Effective Coupling Constants in the Mean-Field Theory
It is shown that the equation of state of nuclear matter can be determined within the mean-field theory of $\sigma \omega$ model provided only that the nucleon effective mass curve is given. We use a family of the possible nucleon effective mass curves that reproduce the empirical saturation point in the calculation of the nuclear binding energy curves in order to obtain density-dependent effective coupling constants. The resulting density-dependent coupling constants may be used to study a possible equation of state of nuclear system at high density or neutron matter. Within the constraints used in this paper to $M^*$ of nuclear matter at saturation point and zero density, neutron matter of large incompressibility is strongly bound at high density while soft neutron matter is weakly bound at low density. The study also exhibits the importance of surface vibration modes in the study of nuclear equation of state.
123098353
Vector Meson Dispersion in Medium
30204992
Quadruple-bend achromatic low emittance lattice studies
A quadruple-bend-achromatic (QBA) cell, defined as a super cell made of two double-bend (DB) cells with different outer and inner dipole bend angles, is found to provide a factor of two in lowering the beam emittance of electron synchrotron light sources. The ratio of bending angles of the inner dipoles to that of the outer dipoles is numerically found to be about 1.5 to 1.6 for an optimal low beam emittance in the isomagnetic condition. The QBA lattice provides an advantage over the double-bend achromat or the double-bend non-achromat in performance by providing some zero dispersion straight- sections and a small natural beam emittance. A lattice with 12 QBA cells with a preliminary dynamic aperture study serves as an example.
96461990
ON MULTIPLE SPIN RESONANCES FOR THE POLARIZED PROTONt
We reformulate the acceleration of polarized protons through a spin resonance in terms of the spin transfer matrix. The method is then applied to the acceleration of polarized protons through nonoverlapping spin resonances. We find that the phase factor between two resonances is important when two resonances have moderate strength. The method has also been applied to resonance jumping. Good agreement with the AGS experiment is achieved. However, when two resonances overlap, no analytic solution is available; we therefore resort to a numerical calculation by solving the system of first-order differential equations. We find that: (i) overlapping resonances can be considered as a single resonance with an effective strength that oscillates rapidly as a function of the spacing of these resonances. Because of this rapid fluctuation, tune spread averaging is also considered. (ii) For isolated resonances, the final spin also oscillates rapidly around a nominal value, which depends solely on the Froissart-Stora equation of individual resonance. Our analytic results in both cases agree very well with the numerical solutions.