Using the production of a Higgs boson in association with a W boson as a test case, we assess the impact of dimension-8 operators within the context of the Standard Model Effective Field Theory. Dimension-8-SM-interference and dimension-6-squared terms appear at the same order in an expansion in 1/Λ, hence dimension-8 effects can be treated as a systematic uncertainty on the new physics inferred from analyses using dimension-6 operators alone. To study the phenomenological consequences of dimension-8 operators, one must first determine the complete set of operators that can contribute to a given process. We accomplish this through a combination of Hilbert series methods, which yield the number of invariants and their field content, and a step-by-step recipe to convert the Hilbert series output into a phenomenologically useful format. The recipe we provide is general and applies to any other process within the dimension ≤ 8 Standard Model Effective Theory. We quantify the effects of dimension-8 by turning on one dimension-6 operator at a time and setting all dimension-8 operator coefficients to the same magnitude. Under this procedure and given the current accuracy on σ(pp → h W + ), we find the effect of dimension-8 operators on the inferred new physics scale to be small, O(few %), with some variation depending on the relative signs of the dimension-8 coefficients and on which dimension-6 operator is considered. The impact of the dimension-8 terms grows as σ(pp → h W + ) is measured more accurately or (more significantly) in high-mass kinematic regions. We provide a FeynRules implementation of our operator set to be used for further more detailed analyses.

Motivated by theories of Neutral Naturalness, we argue that Mirror Stars are a generic possibility in any hidden sector with analogues of Standard Model (SM) electromagnetism and nuclear physics. We show that if there exists a tiny kinetic mixing between the dark photon and the SM photon, Mirror Stars capture SM matter from the interstellar medium, which accumulates in the core of the Mirror Star and radiates in the visible spectrum. This signature is similar to, but in most cases much fainter than, ordinary white dwarfs. We also show for the first time that in the presence of captured SM matter, a fraction of dark photons from the core of the Mirror Star convert directly to SM photons, which leads to an X-ray signal that represents a direct probe of the properties of the Mirror Star core. These two signatures together are a highly distinctive, smoking gun signature of Mirror Stars. We show that Mirror Stars could be discovered in both optical and X-ray searches up to approximately 100-1000 light years away, for a range of well-motivated values of the kinetic mixing parameter.

Non-minimal hidden sectors are an important generic possibility and arise in highly motivated theories like Neutral Naturalness. A fraction of dark matter could therefore have hidden interactions analogous to Standard Matter (SM) electromagnetism and nuclear physics. This leads to the formation of Mirror Stars: dark-sector analogues of regular stars that shine in dark photons. We examine the visible signatures of Mirror Stars in observations for the first time. If the dark and visible photon have a small kinetic mixing, SM matter is captured in Mirror Star cores, giving rise to an optical signal similar to but much fainter than white dwarfs, as well as a separate X-ray signal that represents a direct window into the Mirror Star core. This robust and highly distinctive signature is a smoking gun of Mirror Stars and could be discovered in optical and X-ray searches.

Non-helical tracks are the smoking gun signature of charged and/or colored quirks, which are pairs of particles bound by a new, long-range confining force. We propose a method to efficiently search for these non-helical tracks at the LHC, without the need to fit their trajectories. We show that the hits corresponding to quirky trajectories can be selected efficiently by searching for co-planar hits in the inner layers of the ATLAS and CMS trackers, even in the presence of on average 50 pile-up vertices. We further argue that backgrounds from photon conversions and unassociated pile-up hits can be removed almost entirely, while maintaining a signal reconstruction efficiency as high as ∼70%.With the 300 fb −1 dataset, this implies a discovery potential for string tension between 100 eV and 30 keV, and colored (electroweak charged) quirks as heavy as 1600 (650) GeV may be discovered.

Identifying the inflaton with a pseudo-Goldstone boson explains the flatness of its potential. Successful Goldstone Inflation should also be robust against UV corrections, such as from quantum gravity: in the language of the effective field theory this implies that all scales are sub-Planckian. In this paper we present scenarios which realise both requirements by examining the structure of Goldstone potentials arising from Coleman-Weinberg contributions. We focus on single-field models, for which we notice that both bosonic and fermionic contributions are required and that spinorial fermion representations can generate the right potential shape. We then evaluate the constraints on non-Gaussianity from higher-derivative interactions, finding that axiomatic constraints on Goldstone boson scattering prevail over the current CMB measurements. The fit to CMB data can be connected to the UV completions for Goldstone Inflation, finding relations in the spectrum of new resonances. Finally, we show how hybrid inflation can be realised in the same context, where both the inflaton and the waterfall fields share a common origin as Goldstones.