Abstract
We investigate stringy excitations in Randall-Sundrum effective theories for electroweak symmetry breaking arising from embedding in string theory. RS is dual to a confining gauge theory, which we expect to have “QCD strings”, or color flux tubes. Stringy constructions of RS-like theories allow us to investigate the mass of these string states, which typically grows with a small fractional power of the number of colors N of the dual gauge theory. There are two known strong constraints on N for RS-like theories. The first arises from demanding that the Standard Model gauge couplings do not have a Landau pole at low scales. The second arises from demanding that the first-order confining phase transition in the early universe is able to proceed without leaving an empty universe, i.e. that the rate of bubble nucleation is not too small. We find that these constraints on N imply that string states are generically at most a factor of a few heavier than the lightest KK states, and we cannot self-consistently remain in the limit N,λ ≫ 1. We examine various string constructions of AdS or RS-like backgrounds, including orbifolds, theories on M5-branes, theories on D4-branes, and the recent F-theory construction of Polchinski and Silverstein. In every case we find that there are strong bounds on the mass of new stringy states. We briefly discuss important phenomenological implications due to the presence of such light stringy excitations, such as precision electroweak and flavor observables, as well as collider signals.
Highlights
There are in principle two different embeddings of the Standard Model in such a UV completion
They will be an integral part of the strong dynamics rather than weakly gauging its global symmetry
Using eq 3.7 to specialize to the case of N D3-branes on a cone over an Einstein manifold, we find: bCF T. This is consistent with expectations that bCFT ∼ N, since the matter charged under the global symmetry is a bifundamental of the global symmetry group and the SU(N ) gauge theory dual to our AdS space
Summary
We consider a new strongly-interacting sector which has a group of global symmetries, some of which are gauged by the Standard Model gauge bosons. At leading order in the weak SM gauge couplings, the Standard Model gauge beta functions are modified by the two-point function of the global symmetry current in the strongly-interacting sector. Most RandallSundrum models in the literature do assume that the full Standard Model gauge group is a subgroup of the global symmetry group of the strongly-interacting sector, because it gives a nice way of dealing with flavor. In these models, there is a constraint on bCFT for the SU(3)c currents as well, which numerically is very similar (the QCD coupling is larger but its SM beta function is more asymptotically free). We will revisit this point below, but first we turn to an independent phenomenological bound which applies to the total number of degrees of freedom
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