Alex Kehagias, Antonio Riotto

According to the dS/CFT correspondence, correlators of fields generated during a primordial de Sitter phase are constrained by three-dimensional conformal invariance. Using the properties of radially quantized conformal field theories and the operator-state correspondence, we glean information on some points. The Higuchi bound on the masses of spin-s states in de Sitter is a direct consequence of reflection positivity in radially quantized CFT$_3$ and the fact that scaling dimensions of operators are energies of states. The partial massless states appearing in de Sitter correspond from the boundary CFT$_3$ perspective to boundary states with highest weight for the conformal group. We discuss inflationary consistency relations and the role of asymptotic symmetries which transform asymptotic vacua to new physically inequivalent vacua by generating long perturbation modes. We show that on the CFT$_3$ side, asymptotic symmetries have a nice quantum mechanics interpretation. For instance, acting with the asymptotic dilation symmetry corresponds to evolving states forward (or backward) in "time" and the charge generating the asymptotic symmetry transformation is the Hamiltonian itself. Finally, we investigate the symmetries of anisotropic inflation and show that correlators of four-dimensional free scalar fields can be reproduced in the dual picture by considering an isotropic three-dimensional boundary enjoying dilation symmetry, but with a nonvanishing vacuum expectation value of the boundary stress-energy momentum tensor.

Lunchakorn Tannukij, Pitayuth Wongjun, Sushant G. Ghosh

We derive black string solutions, both charged and uncharged, in de Rham, Gabadadze and Tolley (dRGT) massive gravity, for a generic choice of the parameters in the theory and call it dRGT black string. They are generalization of the Lemos cylindrical solutions. It turns out that the dRGT black string solutions include most of the known black string solutions to the Einstein field equations such as the monopole-black string ones with the coefficients for the third and fourth terms in the potential while the graviton mass in massive gravity naturally generates the cosmological constant and the global monopole term. Further, we compute the mass, temperature, and entropy of dRGT black string and also perform thermodynamic stability of black string. It turns out that the presence of the graviton mass completely changes the black string thermodynamics, and it can provide the Hawking-Page phase transition which is also true for the charged dRGT black string. It turns out that the dRGT black string solutions are thermodynamically stable for $r>r_c$ with negative potential and positive heat capacity, unstable for $r<r_c$ where the potential is positive. The metric of the dRGT black string smoothly goes over to the Lemos solution.

Phongpichit Channuie, Chi Xiong

In this work, we propose a cosmological scenario inherently based on the effective Nambu-Jona-Lasinio (NJL) model that cosmic inflation and dark matter can be successfully described by a single framework. On the one hand, the scalar channel of the NJL model plays a role of the composite inflaton (CI) and we show that it is viable to achieve successful inflation via a non-minimal coupling to gravity. For model of inflation, we compute the inflationary parameters and confront them with recent Planck 2015 data. We discover that the predictions of the model are in excellent agreement with the Planck analysis. We also present in our model a simple connection of physics from the high scales to low scales via renormalization group equations of the physical parameters. On the other hand, the pseudoscalar channel can be assigned as a candidate for composite dark matter (CD). For model of dark matter, we couple the pseudoscalar to the Higgs sector of the standard model with the coupling strength $\kappa$ and estimate its thermally-averaged relic abundance. We discover that the CD mass is strongly sensitive to the coupling $\kappa$. We find in case of light CD, $M_{s}<M_{h}/2$, that the required relic abundance is archived for value of its mass $M_{s} \sim 61\,{\rm GeV}$ for $\kappa=0.1$. However, in this case the CD mass can be lighter when the coupling is getting larger. Moreover, in case of heavy CD, $M_{s}> M_{W,\,Z}$ (or $>M_{h}$), the required relic abundance can be satisfied for value of the CD mass $M_{s}\sim 410\,{\rm GeV}$ for $\kappa = 0.5$. In contradiction to the light mass case, however, the CD mass in this case can even be heavier when the coupling is getting larger.

Antonio Enea Romano

Low-redshift supernovae (SN) has increased the apparent tension between the value of $H_0$ estimated from low and high red-shift observations such as the cosmic microwave background (CMB) radiation. At the same time other observations have provided evidence of the existence of a local underdensity surrounding us up to a red-shift of about $0.07$. We compute with different methods the effects of this local void on the low-redshift luminosity distance using an exact solution of the Einstein's equations, linear perturbation theory and a low-redshift expansion. We find that the dominant effect is the non relativist Doppler red-shift correction, which is proportional to the volume averaged density contrast and to the comoving distance from the center. The red-shift correction can completely resolve the apparent $H_0$ tension. The void affects the megamaser angular diameter distance and the stellar parallax measurements used to calibrate the Cepheids, causing an overall miss-estimation of low red-shift supernovae luminosity distance and consequently of $H_0$. Comparison with previous analysis shows that a compensated void is favored. This effect was not taken into account because the density field maps used to obtain the peculiar velocity were for $z\leq 0.06$, which is not a sufficiently large scale to detect the presence of a local void extending up to $z=0.07$. The void does not affect the high red-shift luminosity distance because the volume averaged density contrast tends to zero asymptotically, making the value of $H_0^{CMB}$ obtained from CMB observations insensitive to the local structure. We propose a method to obtain the monopole component of the local density profile from the deviations of the red-shift uncorrected observed luminosity distance respect to the $\Lambda CDM$ prediction based on cosmological parameters obtained from large scale observations.

Giuseppe Congedo

With the first two detections in late 2015, astrophysics has officially entered into the new era of gravitational wave observations. Since then, much has been going on in the field with a lot of work focussing on the observations and implications for astrophysics and tests of general relativity in the strong regime. However much less is understood about how gravitational detectors really work at their fundamental level. For decades, the response to incoming signals has been customarily calculated using the very same physical principle, which has proved so successful in the first detections. In this paper we review the physical principle that is behind such a detection at the very fundamental level, and we try to highlight the peculiar subtleties that make it so hard in practice. We will then mention how detectors are built starting from this fundamental measurement element.

Todd A. Brun, Mark M. Wilde

Proposed models of closed timelike curves (CTCs) have been shown to enable powerful information-processing protocols. We examine the simulation of models of CTCs both by other models of CTCs and by physical systems without access to CTCs. We prove that the recently proposed transition probability CTCs (T-CTCs) are physically equivalent to postselection CTCs (P-CTCs), in the sense that one model can simulate the other with reasonable overhead. As a consequence, their information-processing capabilities are equivalent. We also describe a method for quantum computers to simulate Deutschian CTCs (but with a reasonable overhead only in some cases). In cases for which the overhead is reasonable, it might be possible to perform the simulation in a table-top experiment. This approach has the benefit of resolving some ambiguities associated with the equivalent circuit model of Ralph et al. Furthermore, we provide an explicit form for the state of the CTC system such that it is a maximum-entropy state, as prescribed by Deutsch.