Exploring the small mass limit of stationary black holes in theories with Gauss-Bonnet terms

In this work we examine the small mass limit of black holes (BHs), with and without spin, in theories where a scalar field is non-minimally coupled to a Gauss–Bonnet (GB) term. First, we provide an analytical example for a theory where a static closed-form solution with a small mass limit is known, and later use analytical and numerical techniques to explore this limit in standard scalar-GB theories with dilatonic, linear and quadratic-exponential couplings. In most cases studied here, we find an inner singularity that overlaps with the event horizon of the static BH as the small mass limit is reached. Moreover, since solutions in this limit possess a non-vanishing Hawking temperature, a naked singularity is expected to be reached through evaporation, raising questions concerning the consistency of these theories altogether. On the other hand, we provide for the first time in this context an example of a coupling where the small mass limit is never reached, thus preferred from the point of view of cosmic censorship. Finally, we consider BHs with spin and numerically investigate how this changes the picture, using these to place the tightest upper bounds to date on the coupling constant for the dilatonic and linear theories, with α‾<1 km

Observational constraints on the regularized 4D Einstein-Gauss-Bonnet theory of gravity

In this paper we study the observational constraints that can be imposed on the coupling parameter, $\hat \alpha$, of the regularized version of the 4-dimensional Einstein-Gauss-Bonnet theory of gravity. We use the scalar-tensor field equations of this theory to perform a thorough investigation of its slow-motion and weak-field limit, and apply our results to observations of a wide array of physical systems that admit such a description. We find that the LAGEOS satellites are the most constraining, requiring $| \hat \alpha | \lesssim 10^{10} \,{\rm m}^2$. This constraint suggests that the possibility of large deviations from general relativity is small in all systems except the very early universe ($t<10^{-3}\, {\rm s}$), or the immediate vicinity of stellar-mass black holes ($M\lesssim100\, M_{\odot}$). We then consider constraints that can be imposed on this theory from cosmology, black hole systems, and table-top experiments. It is found that early universe inflation prohibits all but the smallest negative values of $\hat \alpha$, while observations of binary black hole systems are likely to offer the tightest constraints on positive values, leading to overall bounds $0 \lesssim \hat \alpha \lesssim 10^8 \, {\rm m}^2$.Comment: 17 page

Radiata : an economic breeding objective : the definition of an economic breeding objective for plantation radiata pine grown to produce timber flitch and newsprint and an investigation of some aspects related to short-rotation breeding in general using plantation eucalypts as an example

An economic breeding objective was defined for unpruned radiata pine grown to produce structural grade timber flitch and high brightness newsprint from thermomechanical pulp (TMP) in Australia. A production enterprise model was developed including all sources of income (sale of flitch and newsprint) and costs (including growing, harvesting, transporting and mill processing components). The enterprise, as modelled, was shown to be profitable (Profitability Index 19.9%, assuming a discount rate of 5%). The majority of wood volume was assumed to be utilised to produce high brightness newsprint (77% by volume), with only 23% used to produce rough green flitch. The effect of future changes in growth, bark volume, stem sweep, stem taper, branch quality, timber strength, basic density, tracheid length, tracheid coarseness and wood brightness (breeding objective traits) on the profitability of this production enterprise was modelled by defining profit functions relating each of these traits to the economics of each stage of production. Sensitivity analysis was employed throughout this process to examine which assumptions were driving profitability, and identify any that may need verification. For each trait an economic weight was estimated as the incremental Profitability Index associated with a unit increa, se in each trait. Basic density, mean tracheid length and wood brightness were demonstrated as having a major effect on the production of high brightness newsprint from TMP. Growth, as expected, had a large impact on the cost of growing a plantation, however was predicted to be only of moderate to low importance in increasing enterprise profitbability overall. Branch index was shown to have a major impact on the profitability of the flitch production line of the enterprise. Bark volume, stem sweep, stem taper and tracheid coarseness appeared to have a very low impact on production system profitability. However, the importance of stem sweep and stem taper as well as branch index and timber strength are likely to become more important if the enterprise increases its production ratio of flitch to newsprint. An investigation into multi-trait selection strategies clearly demonstrated the dominance of basic density as a selection trait on enterprise profitability. The assessment of wood and tracheid properties is much more costly than assessment of growth and form traits. However it was demonstrated that the gains predicted from individual-tree selections compared with selection based on family-means for basic density and tracheid length are significant and well worth the additional associated cost

The 4D Einstein-Gauss-Bonnet theory of gravity: a review

57 pages, 2 figures57 pages, 2 figure

Black Holes in the Scalar-Tensor Formulation of 4D Einstein-Gauss-Bonnet Gravity: Uniqueness of Solutions, and a New Candidate for Dark Matter

In this work we study static black holes in the regularized 4D Einstein-Gauss-Bonnet theory of gravity; a shift-symmetric scalar-tensor theory that belongs to the Horndeski class. This theory features a simple black hole solution that can be written in closed form, and which we show is the unique static, spherically-symmetric and asymptotically-flat black hole vacuum solution of the theory. We further show that no asymptotically-flat, time-dependent, spherically-symmetric perturbations to this geometry are allowed, which suggests that it may be the only spherically-symmetric vacuum solution that this theory admits (a result analogous to Birkhoff's theorem). Finally, we consider the thermodynamic properties of these black holes, and find that their final state after evaporation is a remnant with a size determined by the coupling constant of the theory. We speculate that remnants of this kind from primordial black holes could act as dark matter, and we constrain the parameter space for their formation mass, as well as the coupling constant of the theory

Derivation of regularized field equations for the Einstein-Gauss-Bonnet theory in four dimensions

6 pages + 2 pages with reference