# Ghost-free theory with third-order time derivatives [CL]

As the first step to extend our understanding of higher-derivative theories, within the framework of analytic mechanics of interacting particles, we construct a ghost-free theory involving third-order time derivative in Lagrangian. We clarify that there is a crucial difference in construction from up-to-second-order-derivative theories. While eliminating linear momentum terms in the Hamiltonian is necessary and sufficient to kill the ghosts associated with the higher derivatives for the Lagrangian with up to second-order derivatives, this is necessary but not sufficient for the Lagrangian with higher than second-order derivatives. We demonstrate that even after eliminating the linear momentum terms ghosts are still lurking and they need to be removed appropriately to make Lagrangian free from the ghosts. We clarify a set of ghost-free conditions under which we show that the Hamiltonian is bounded, and that equations of motion are reducible into a second-order system.

H. Motohashi, T. Suyama and M. Yamaguchi
Thu, 23 Nov 17
32/52

# Fluctuations through a Vibrating Bounce [CL]

We study the evolution of cosmological perturbations in a non-singular bouncing cosmology with a bounce phase which has superimposed oscillations of the scale factor. We identify length scales for which the final spectrum of fluctuations obtains imprints of the non-trivial bounce dynamics. These imprints in the spectrum are manifested in the form of damped oscillation features at scales smaller than a characteristic value and an increased reddening of the spectrum at all the scales as the number of small bounces increases.

R. Brandenberger, Q. Liang, R. Ramos, et. al.
Thu, 23 Nov 17
38/52

# Natural cliff inflation [CL]

We propose a novel scenario of inflation, in which the inflaton is identified as the lightest mode of an angular field in a compactified fifth dimension. The periodic effective potential exhibits exponentially flat plateaus, so that a sub-Planckian field excursion without hilltop initial conditions is naturally realized. We can obtain consistent predictions with observations on the spectral index and the tensor-to-scalar ratio.

J. Gong and C. Shin
Thu, 23 Nov 17
40/52

# Black branes and black strings in the astrophysical and cosmological context [CL]

We consider Kaluza-Klein models where internal spaces are compact flat or curved Einstein spaces. This background is perturbed by a compact gravitating body with the dust-like equation of state (EoS) in the external/our space and an arbitrary EoS parameter $\Omega$ in the internal space. Without imposing any restrictions on the form of the perturbed metric and the distribution of the perturbed energy densities, we perform the general analysis of the Einstein and conservation equations in the weak-field limit. All conclusions follow from this analysis. For example, we demonstrate that the perturbed model is static and perturbed metric preserves the block-diagonal form. In a particular case $\Omega=-1/2$, the found solution corresponds to the weak-field limit of the black strings/branes. The black strings/branes are compact gravitating objects which have the topology (four-dimensional Schwarzschild spacetime)$\times$ ($d$-dimensional internal space) with $d\geq 1$. We present the arguments in favour of these objects. First, they satisfy the gravitational tests for the parameterized post-Newtonian parameter $\gamma$ at the same level of accuracy as General Relativity. Second, they are preferable from the thermodynamical point of view. Third, averaging over the Universe, they do not destroy the stabilization of the internal space. These are the astrophysical and cosmological aspects of the black strings/branes.

O. Akarsu, A. Chopovsky and A. Zhuk
Thu, 23 Nov 17
50/52

Comments: 7 pages, no figures and tables

# Transitions between topologically non-trivial configurations [CL]

We study formation and evolution of solitons within a model with two real scalar fields with the potential having a saddle point. The set of these configurations can be split into disjoint equivalence classes. We give a simple expression for the winding number of an arbitrary closed loop in the field space and discuss the evolution scenarios that change the winding number. These non-trivial field configurations lead to formation of the domain walls in the three-dimensional physical space.

V. Gani, A. Kirillov and S. Rubin
Thu, 23 Nov 17
52/52

Comments: 5 pages, 2 figures; Proceedings of the 3rd International Conference on Particle Physics and Astrophysics, Moscow, 2-5 October 2017

# Black branes and black strings in the astrophysical and cosmological context [CL]

We consider Kaluza-Klein models where internal spaces are compact flat or curved Einstein spaces. This background is perturbed by a compact gravitating body with the dust-like equation of state (EoS) in the external/our space and an arbitrary EoS parameter $\Omega$ in the internal space. Without imposing any restrictions on the form of the perturbed metric and the distribution of the perturbed energy densities, we perform the general analysis of the Einstein and conservation equations in the weak-field limit. All conclusions follow from this analysis. For example, we demonstrate that the perturbed model is static and perturbed metric preserves the block-diagonal form. In a particular case $\Omega=-1/2$, the found solution corresponds to the weak-field limit of the black strings/branes. The black strings/branes are compact gravitating objects which have the topology (four-dimensional Schwarzschild spacetime)$\times$ ($d$-dimensional internal space) with $d\geq 1$. We present the arguments in favour of these objects. First, they satisfy the gravitational tests for the parameterized post-Newtonian parameter $\gamma$ at the same level of accuracy as General Relativity. Second, they are preferable from the thermodynamical point of view. Third, averaging over the Universe, they do not destroy the stabilization of the internal space. These are the astrophysical and cosmological aspects of the black strings/branes.

O. Akarsu, A. Chopovsky and A. Zhuk
Thu, 23 Nov 17
3/52

Comments: 7 pages, no figures and tables

# Fluctuations through a Vibrating Bounce [CL]

We study the evolution of cosmological perturbations in a non-singular bouncing cosmology with a bounce phase which has superimposed oscillations of the scale factor. We identify length scales for which the final spectrum of fluctuations obtains imprints of the non-trivial bounce dynamics. These imprints in the spectrum are manifested in the form of damped oscillation features at scales smaller than a characteristic value and an increased reddening of the spectrum at all the scales as the number of small bounces increases.

R. Brandenberger, Q. Liang, R. Ramos, et. al.
Thu, 23 Nov 17
11/52