ترغب بنشر مسار تعليمي؟ اضغط هنا

Emulating $Lambda$CDM-like expansion on the Phantom brane

65   0   0.0 ( 0 )
 نشر من قبل Satadru Bag
 تاريخ النشر 2018
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

In [Schmidt PRD 80 123003 (2009)], the author suggested that dynamical dark energy (DDE) propagating on the phantom brane could mimick $Lambda$CDM. Schmidt went on to derive a phenomenological expression for $rho_{rm DE}$ which could achieve this. We demonstrate that while Schmidts central premise is correct, the expression for $rho_{rm DE}$ derived in Schmidt (2009) is flawed. We derive the correct expression for $rho_{rm DE}$ which leads to $Lambda$CDM-like expansion on the phantom brane. We also show that DDE on the brane can be associated with a Quintessence field and derive a closed form expression for its potential $V(phi)$. Interestingly the $alpha$-attractor based potential $V(phi) propto coth^2{lambdaphi}$ makes braneworld expansion resemble $Lambda$CDM. However the two models can easily be distinguished on the basis of density perturbations which grow at different rates on the braneworld and in $Lambda$CDM.



قيم البحث

اقرأ أيضاً

We derive an analytical expression for the growth rate of matter density perturbations on the phantom brane (which is the normal branch of the Dvali-Gabadadze-Porrati model). This model is characterized by a phantomlike effective equation of state fo r dark energy at the present epoch. It agrees very well with observations. We demonstrate that the traditional parametrization $f=Omega_m^gamma$ with a quasiconstant growth index $gamma$ is not successful in this case. Based on a power series expansion at large redshifts, we propose a different parametrization for this model: $f=Omega_m^gammaleft(1+frac{b}{ell H}right)^beta$, where $beta$ and $b$ are constants. Our numerical simulations demonstrate that this new parametrization describes the growth rate with great accuracy - the maximum error being $leq 0.1%$ for parameter values consistent with observations.
We show that a cosmology driven by gravitationally induced particle production of all non-relativistic species existing in the present Universe mimics exactly the observed flat accelerating $Lambda$CDM cosmology with just one dynamical free parameter . This kind of scenario includes the creation cold dark matter (CCDM) model [Lima, Jesus & Oliveira, JCAP 011(2010)027] as a particular case and also provides a natural reduction of the dark sector since the vacuum component is not needed to accelerate the Universe. The new cosmic scenario is equivalent to $Lambda$CDM both at the background and perturbative levels and the associated creation process is also in agreement with the universality of the gravitational interaction and equivalence principle. Implicitly, it also suggests that the present day astronomical observations cannot be considered the ultimate proof of cosmic vacuum effects in the evolved Universe because $Lambda$CDM may be only an effective cosmology.
137 - Artur Alho , Claes Uggla 2015
This paper treats nonrelativistic matter and a scalar field $phi$ with a monotonically decreasing potential minimally coupled to gravity in flat Friedmann-Lema^{i}tre-Robertson-Walker cosmology. The field equations are reformulated as a three-dimensi onal dynamical system on an extended compact state space, complemented with cosmographic diagrams. A dynamical systems analysis provides global dynamical results describing possible asymptotic behavior. It is shown that one should impose emph{global and asymptotic} bounds on $lambda=-V^{-1},dV/dphi$ to obtain viable cosmological models that continuously deform $Lambda$CDM cosmology. In particular we introduce a regularized inverse power-law potential as a simple specific example.
We propose a novel model in the framework of $f(Q)$ gravity, which is a gravitational modification class arising from the incorporation of non-metricity. The model has General Relativity as a particular limit, it has the same number of free parameter s to those of $Lambda$CDM, however at a cosmological framework it gives rise to a scenario that does not have $Lambda$CDM as a limit. Nevertheless, confrontation with observations at both background and perturbation levels, namely with Supernovae type Ia (SNIa), Baryonic Acoustic Oscillations (BAO), cosmic chronometers (CC), and Redshift Space Distortion (RSD) data, reveals that the scenario, according to AIC, BIC and DIC information criteria, is in some datasets slightly preferred comparing to $Lambda$CDM cosmology, although in all cases the two models are statistically indiscriminate. Finally, the model does not exhibit early dark energy features, and thus it immediately passes BBN constraints, while the variation of the effective Newtons constant lies well inside the observational bounds.
We present an explicit detailed theoretical and observational investigation of an anisotropic massive Brans-Dicke (BD) gravity extension of the standard $Lambda$CDM model, wherein the extension is characterized by two additional degrees of freedom; t he BD parameter, $omega$, and the present day density parameter corresponding to the shear scalar, $Omega_{sigma^2,0}$. The BD parameter, determining the deviation from general relativity (GR), by alone characterizes both the dynamics of the effective dark energy (DE) and the redshift dependence of the shear scalar. These two affect each other depending on $omega$, namely, the shear scalar contributes to the dynamics of the effective DE, and its anisotropic stress --which does not exist in scalar field models of DE within GR-- controls the dynamics of the shear scalar deviating from the usual $propto(1+z)^6$ form in GR. We mainly confine the current work to non-negative $omega$ values as it is the right sign --theoretically and observationally-- for investigating the model as a correction to the $Lambda$CDM. By considering the current cosmological observations, we find that $omegagtrsim 250$, $Omega_{sigma^2,0}lesssim 10^{-23}$ and the contribution of the anisotropy of the effective DE to this value is insignificant. We conclude that the simplest anisotropic massive BD gravity extension of the standard $Lambda$CDM model exhibits no significant deviations from it all the way to the Big Bang Nucleosynthesis. We also point out the interesting features of the model in the case of negative $omega$ values; for instance, the constraints on $Omega_{sigma^2,0}$ could be relaxed considerably, the values of $omegasim-1$ (relevant to string theories) predict dramatically different dynamics for the expansion anisotropy.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا