3,945 research outputs found
Gauge-flation vs chromo-natural inflation
No full textAbstractGauge-flation, non-Abelian gauge field inflation, which was introduced in Maleknejad and Sheikh-Jabbari (2011) [4] and analyzed more thoroughly in Maleknejad and Sheikh-Jabbari (2011) [5], is a model of inflation driven by non-Abelian gauge fields minimally coupled to Einstein gravity. In this model a certain rotationally invariant combination of gauge fields plays the role of the inflaton. Recently, the chromo-natural inflation model was proposed (Adshead and Wyman, 2012 [8]) which besides the non-Abelian gauge fields also involves an axion field. In this short Letter we show that the model involving axions, indeed allows for various slow-roll trajectories for different values of its parameters: A specific trajectory discussed in Adshead and Wyman (2012) [8] starts from a “small axion” region, while the trajectory considered in Maleknejad and Sheikh-Jabbari (2011) [4,5] corresponds to a “large axion” region
On black hole temperature in Horndeski gravity
No full textIt has been observed that for black holes in certain family of Horndeski gravity theories Wald's entropy formula does not lead to the correct first law for black hole thermodynamics. For this family of Horndeski theories speeds of propagation of gravitons and photons are in general different and gravitons move on an effective metric different than the one seen by photons. We show that the temperature of the black hole should be modified from surface gravity over 2π to include effects of this effective metric. The modified temperature, with the entropy unambiguously computed by the solution phase space method, yields the correct first law. Our results have far reaching implications for the Hawking radiation and species problem, going beyond the Horndeski theories
Gauged M-flation after BICEP2
No full textIn view of the recent BICEP2 results [arXiv:1403.3985] which may be attributed to the observation of B-modes polarization of the CMB with tensor-to-scalar ratio r=0.2−0.05+0.07, we revisit M-flation model. Gauged M-flation is a string theory motivated inflation model with Matrix valued scalar inflaton fields in the adjoint representation of a U(N) Yang–Mills theory. In continuation of our previous works, we show that for a class of M-flation models the action for these inflaton fields can be such that the “effective inflaton field” ϕ has a double-well Higgs-like potential, with minima at ϕ=0,μ. We focus on the ϕ>μ, symmetry-breaking region. We thoroughly examine predictions of the model for r in the 2σ region allowed for nS by the Planck experiment. As computed in [arXiv:0903.1481], for Ne=60 and nS=0.96 we find r≃0.2, which sits in the sweet spot of BICEP2 region for r. We find that with increasing μ arbitrarily, nS cannot go beyond ≃0.9670, the scalar spectral index for the quadratic chaotic potential. As nS varies in the 2σ range which is allowed by Planck and could be reached by the model, r varies in the range [0.13,0.26]. Future cosmological experiments, like the CMBPOL, that confines nS with σ(nS)=0.0029 can constrain the model further. Also, in this region of potential, for nS=0.9603, we find that the largest isocurvature mode, which is uncorrelated with curvature perturbations, has a power spectrum with the amplitude of order 10−11 at the end of inflation. We also discuss the range of predictions of r in the hilltop region, ϕ<μ
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