Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe double-soft limit in cosmological correlation functions and graviton exchange effects
92
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The graviton exchange effect on cosmological correlation functions is examined by employing the double-soft limit technique. A new relation among correlation functions that contain the effects due to graviton exchange diagrams in addition to those due to scalar-exchange and scalar-contact-interaction, is derived by using the background field method and independently by the method of Ward identities associated with dilatation symmetry. We compare these three terms, putting small values for the slow-roll parameters and $(1-n_{s}) = 0.042$, where $n_{s}$ is the scalar spectral index. It is argued that the graviton exchange effects are more dominant than the other two and could be observed in the trispectrum in the double-soft limit. Our observation strengthens the previous work by Seery, Sloth and Vernizzi, in which it has been argued that the graviton exchange dominates in the counter-collinear limit for single field slow-roll inflation.
rate research
Read More
It is now well understood that Ward identities associated to the (extended) BMS algebra are equivalent to single soft graviton theorems. In this work, we show that if we consider nested Ward identities constructed out of two BMS charges, a class of double soft factorization theorems can be recovered. By making connections with earlier works in the literature, we argue that at the sub-leading order, these double soft graviton theorems are the so-called consecutive double soft graviton theorems. We also show how these nested Ward identities can be understood as Ward identities associated to BMS symmetries in scattering states defined around (non-Fock) vacua parametrized by supertranslations or superrotations.
Recently it was conjectured that a certain infinite-dimensional diagonal subgroup of BMS supertranslations acting on past and future null infinity (${mathscr I}^-$ and ${mathscr I}^+$) is an exact symmetry of the quantum gravity ${cal S}$-matrix, and an associated Ward identity was derived. In this paper we show that this supertranslation Ward identity is precisely equivalent to Weinbergs soft graviton theorem. Along the way we construct the canonical generators of supertranslations at ${mathscr I}^pm$, including the relevant soft graviton contributions. Boundary conditions at the past and future of ${mathscr I}^pm$ and a correspondingly modified Dirac bracket are required. The soft gravitons enter as boundary modes and are manifestly the Goldstone bosons of spontaneously broken supertranslation invariance.
We show that the form of the recently proposed subleading soft graviton and gluon theorems in any dimension are severely constrained by elementary arguments based on Poincare and gauge invariance as well as a self-consistency condition arising from the distributional nature of scattering amplitudes. Combined with the assumption of a local form as it would arise from a Ward identity the orbital part of the subleading operators is completely fixed by the leading universal Weinberg soft pole behavior. The polarization part of the differential subleading soft operators in turn is determined up to a single numerical factor for each hard leg at every order in the soft momentum expansion. In four dimensions, factorization of the Lorentz group allows to fix the subleading operators completely.
We study instanton corrections to four-point correlation correlation function of half-BPS operators in $mathcal N=4$ SYM in the light-cone limit when operators become null separated in a sequential manner. We exploit the relation between the correlation function in this limit and light-like rectangular Wilson loop to determine the leading instanton contribution to the former from the semiclassical result for the latter. We verify that the light-like rectangular Wilson loop satisfies anomalous conformal Ward identities nonperturbatively, in the presence of instantons. We then use these identities to compute the leading instanton contribution to the light-like cusp anomalous dimension and to anomalous dimension of twist-two operators with large spin.
We explore the possibility to make use of cosmological data to look for signatures of unknown heavy particles whose masses are on the order of the Hubble parameter during the time of inflation. To be more specific we take up the quasi-single field inflation model, in which the isocurvaton $sigma $ is supposed to be the heavy particle. We study correlation functions involving both scalar ($zeta $) and tensor ($gamma $) perturbations and search for imprints of the $sigma$-particle effects. We make use of the technique of the effective field theory for inflation to derive the $zeta sigma $ and $gamma zeta sigma $ couplings. With these couplings we compute the effects due to $sigma $ to the power spectrum $langle zeta zeta rangle $ and correlations $langle gamma^{s} zeta zeta rangle$ and $langle gamma^{s_{1}} gamma ^{s_{2}} zeta zeta rangle $, where $s$, $s_{1}$ and $s_{2}$ are the polarization indices of gravitons. Numerical analyses of the $sigma$-mass effects to these corrlations are presented. It is argued that future precise observations of these correlations could make it possible to measure the $sigma$-mass and the strength of the $zeta sigma$ and $gamma zeta sigma$ couplings. As an extension to the $N$-graviton case we also compute the correlations $langle gamma ^{s_{1}} cdots gamma ^{s_{N}} zeta zeta rangle $ and $langle gamma ^{s_{1}} cdots cdots gamma ^{s_{2N}} zeta zeta rangle $ and their $sigma$-mass effects. It is suggested that larger $N$ correlation functions are useful to probe larger $sigma$-mass .
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
