Scales of gravity

Abstract

We propose a framework in which the quantum gravity scale can be as low as 10 Ϫ3 eV. The key assumption is that the standard model ultraviolet cutoff is much higher than the quantum gravity scale. This ensures that we observe conventional weak gravity. We construct an explicit brane-world model in which the brane-localized standard model is coupled to strong 5D gravity of infinite-volume flat extra space. Because of the high ultraviolet scale, the standard model fields generate a large graviton kinetic term on the brane. This kinetic term ''shields'' the standard model from the strong bulk gravity. As a result, an observer on the brane sees weak 4D gravity up to astronomically large distances beyond which gravity becomes five dimensional. Modeling quantum gravity above its scale by the closed string spectrum we show that the shielding phenomenon protects the standard model from an apparent phenomenological catastrophe due to the exponentially large number of light string states. The collider experiments, astrophysics, cosmology and gravity measurements independently point to the same lower bound on the quantum gravity scale, 10 Ϫ3 eV. For this value the model has experimental signatures both for colliders and for submillimeter gravity measurements. Black holes reveal certain interesting properties in this framework.

Induced gravity in orientifold models

“…Whereas the RandallSundrum setup leads to a four-dimensional behaviour of gravity at long distances and a five-dimensional behaviour of gravity at short distances (that is similar to compactification) in the case of the Dvali-Gabadadze-Porrati 1 setup gravity is four-dimensional at short distances and five-dimensional at long distances. Therefore to be consistent with experiments and astronomical observations the cross-over scale has either to be astronomically large or one has to compactify the extra dimension [7]. In the later case KaluzaKlein graviton emission is suppressed in the ultraviolet and therefore also the energy loss from brane to bulk.…”

“…we can have a four-dimensional Einstein-Hilbert term that is induced on a 3-brane by the fields that live on the 3-brane. This has been put forward by Dvali, Gabadadze and Porrati ( [4] - [6]). Obviously we can also combine these three ideas in a given model.…”

Physics of trans-Planckian gravity

“…In quantum field theory any measurement that attempts to resolve the distance L has to excite, via a scattering experiment, degrees of freedom of energy 1/L within the box of size L. The explicit construction of such a scattering experiment would involve at least two particles which are boosted in such a way that their (Lorentz-invariant) center of mass energy exceeds 1/L and that their impact parameter will be less than L. For L ≪ L P such an attempt will lead to the formation of a classical BH (see also [6,[9][10][11]). Note, that by itself none of the involved boosted particles is a BH even when boosted to energies ≫ M P as no graviton exchange is involved.…”

“…The discovery of low scale quantum gravity scenarios [8,9] promoted this possibility to a potentially experimentallyobservable phenomenon. Indeed, BH formation in high energy scatterings at particle colliders was predicted in [9] (for subsequent work in this direction see [10]). This feature of gravity was formulated in terms of the "Asymptotic Darkness" as a unique outcome of Trans-Planckian scattering at small impact parameter in [11].…”

D‐branes in Standard Model building, gravity and cosmology

“…Since BIG is dominating in the UV, it suppresses the emission of KK gravitons in that regime, that would have been otherwise unsuppressed. A calculation of the value of the wave-function of graviton KK states of mass m, in this case gives |φ m (0)| 2 ∼ (4 + m 2 r 2 c ) −1 [185]. This value is the classical coupling constant, controlling the emission of the KK states.…”