Generalized modified gravity in large extra dimensions

Abstract

We discuss effective interactions among brane matter induced by modifications of higher-dimensional Einstein gravity through the replacement of Einstein-Hilbert term with a generic function f ( R, RA B RA B, RA B C D RA B C D ) of the curvature tensors. We determine gravi-particle spectrum of the theory, and perform a comparative analysis of its predictions with those of the Einstein gravity within Arkani-Hamed-Dvali-Dimopoulos (ADD) setup. We find that this general higher-curvature quantum gravity theory contributes to scatterings among both massive and massless brane matter (in contrast to much simpler generalization of the Einstein gravity, f ( R ), which influences only the massive matter), and therefore, can be probed via various scattering processes at present and future colliders and directly confronted with the ADD expectations. In addition to collision processes which proceed with tree-level gravi-particle exchange, effective interactions among brane matter are found to exhibit a strong sensitivity to higher-curvature gravity via the gravi-particle loops. Furthermore, particle collisions with missing energy in their final states are found to be sensitive to additional gravi-particles not found in Einstein gravity. In general, road to a correct description of quantum gravity above Fermi energies depends crucially on if collider and other search methods end up with a negative or positive answer for the presence of higher-curvature gravitational interactions.Turkish Academy of Sciences and TÜBİTAK project 104T50

Conformal transformations in metric‐affine gravity and ghosts

“…The transformed frame consists of no ghost field, and exhibits emergent conformal invariance (sometimes called Weyl-Stückelberg invariance). The results can have far-reaching consequences for collider experiments [12,25], cosmological evolution [5,28,33] as well as electroweak breaking [11].…”

“…as was the case for metrical gravity, defined in (14). Therefore, though the original action (15) exhibits no sign of conformal invariance and hence the new action (22) arises, this transformed action exhibits manifest conformal invariance.…”

“…This is a built-in property of the system; this is common to 'transformations' including the gauge transformations. -Another point to notice about (11) is that the scalar field φ (which is a function of the conformal factor Ω) is a ghost [11][12][13]. This is an unavoidable feature if gravity is to be an attractive force.…”

“…This is a highly important result since it generalizes the very concept of 'conformal coupling' between scalar fields and curvature scalar by changing ζ D to ζ D . This modification can have noticeable consequences in cosmological [5,23,24] as well as collider observables [12,25] of GR with affinity. -In complete contrast to (11), the scalar field φ in (31) obtains an indefinite kinetic term.…”

“…• Another point to notice about (11) is that the scalar field φ (which is a function of the conformal factor Ω) is a ghost [13][14][15]. This is an unavoidable feature if gravity is to be an attractive force.…”