Higher curvature quantum gravity and large extra dimensions

Abstract

We discuss effective interactions among brane matter induced by modifications of higher dimensional Einstein gravity via the replacement of Einstein-Hilbert term with a generic function f (R) of the curvature scalar R. After deriving the graviton propagator, we analyze impact of virtual graviton exchanges on particle interactions, and conclude that f (R) gravity effects are best probed by high-energy processes involving massive gauge bosons, heavy fermions or the Higgs boson. We perform a comparative analysis of the predictions of f (R) gravity and of Arkani-HamedDvali-Dimopoulos (ADD) scenario, and find that the former competes with the latter when f (0) is positive and comparable to the fundamental scale of gravity in higher dimensions. In addition, we briefly discuss graviton emission from the brane as well as its decays into brane-localized matter, and find that they hardly compete with the ADD expectations. Possible existence of higher-curvature gravitational interactions in large extra spatial dimensions opens up various signatures to be confronted with existing and future collider experiments.

Generalized modified gravity in large extra dimensions

“…While the former plays a crucial role in cosmological and astrophysical contexts, the latter constitutes one of the most important signatures of extra dimensions at colliders in that gravi-particle emission from the brane gives rise to scattering processes with single missing energy signal, and thus, it is of fundamental importance for distinguishing supersymmetric models from the extra dimensional ones. In these real gravi-particle involving processes the presence of bulk masses for tensor and scalar modes modify decay signatures significantly, as has been detailed in [11].…”

“…A highly interesting aspect of (19) with the replacements (24) is that effects of the modified gravity (due to the massive ghosty J = 2 graviton) survive even in the limit of massless fermions. This is , as one recalls form [11], not the case for f (R) gravity to which only scatterings of the massive brane matter exhibit sensitivity. This property of f (R, P, Q) gravity is important in that its effects can be directly probed at high-energy colliders (where colliding beams of matter are essentially massless) and effective higherdimensional operators consisting of light fermions.…”

“…The dominant contribution to gravi-particle emission comes from Kaluza-Klein levels in the vicinity of R 2 (M 2 Z − m 2 gravi−particle ). However, one here notes an important aspect of gravi-particle decay/emission processes: For such processes all gravi-particles must be fields with positive semi-definite mass-squareds and hence, as in f (R) gravity [11], one does not expect significant contributions from gravi-particles other than J = 0 graviton (see the figures Fig. 1-4).…”

“…The tree-level gravi-particle exchange, as has been detailed in the last section, gives rise to anomalous interactions among brane matter species [5,6,11]. The on-brane processes are entirely tree-level ones in such processes; however, they exhibit appreciable sensitivity to gravi-particle exchange due to rather high virtualities that gravi-particles obtain via their propagation through the extra dimensions.…”

“…heavy fermions, weak bosons and the Higgs boson (for recent work on Lovelock gravity see [12]). The reason is that f (R) theory is equivalent to Einstein gravity plus an independent scalar field theory, and it is the propagation of this additional scalar that causes observable differences between the f (R) gravity and ADD setup in high energy processes [11].…”