I show that the neutral pion decay in B→K(∗)π0γ, with π0→eeγ, might generate large sources of lepton flavor universality violation (LFUV) in measurements of the ratios, RK(∗): If the photons in the K(∗)eeγγ final state are reconstructed as bremsstrahlung, the recovered electron-positron invariant mass can be pushed into the 1-6 GeV2 signal region, artificially enhancing the measured B→K(∗)ee branching ratio compared to B→K(∗)μμ. I present a conservative estimate and simulation of the B→Kπ0γ LFUV background at LHCb, that together suggest this effect could reduce the recovered RK up to several percent. A reliable assessment of the size of this effect will require dedicated simulations within experimental frameworks themselves.

The neutral component of a real pseudoscalar electroweak (EW) triplet can produce a diphoton excess at 750 GeV, if it is somewhat mixed with an EW singlet pseudoscalar. This triplet-singlet mixing allows for greater freedom in the diboson branching ratios than the singlet-only case, but it is still possible to probe the parameter space extensively with 300 fb-1. The charged component of the triplet is pair produced at the LHC, which results in a striking signal in the form of a pair of Wγ resonances with an irreducible rate of 0.27 fb. Other signatures include multiboson final states from cascade decays of the triplet-singlet neutral states. A large class of composite models feature both EW singlet and triplet pseudo-Nambu-Goldstone bosons in their spectrum, with the diboson couplings generated by axial anomalies.

A dark QCD sector is a relatively minimal extension of the Standard Model (SM) that admits Dark Matter (DM) candidates, but requires no portal to the visible sector beyond gravitational interactions: a "nightmare scenario"for DM detection. We consider a secluded dark sector containing a single flavor of light, vector-like dark quark gauged under (N). In the large-N limit, this single-flavor theory becomes highly predictive, generating two DM candidates whose masses and dynamics are described by few parameters: a light quark-antiquark bound state, the dark analog of the η' meson, and a heavy bound state of N quarks, the dark analog of the Δ++ baryon. We show that the latter may freeze-in with an abundance independent of the confinement scale, forming DM-like relics for N ≲ 10, while the former may generate DM via cannibalization and freeze-out. We study the interplay of this two-component DM system, and determine the characteristic ranges of the confinement scale, dark-visible sector temperature ratio, and N that admit non-excluded DM, once effects of self-interaction constraints and bounds on effective degrees of freedom at the BBN and CMB epochs are included.

We derive compact expressions for the helicity amplitudes of the many-body B → D(∗)(→ DY)τ(→ Xν)ν decays, specifically for X = ℓν or π and Y = π or γ. We include contributions from all ten possible new physics four-Fermi operators with arbitrary couplings. Our results capture interference effects in the full phase space of the visible τ and D∗ decay products which are missed in analyses that treat the τ or D∗ or both as stable. The τ interference effects are sizable, formally of order mτ/mB for the standard model, and may be of order unity in the presence of new physics. Treating interference correctly is essential when considering kinematic distributions of the τ or D∗ decay products, and when including experimentally unavoidable phase space cuts. Our amplitude-level results also allow for efficient exploration of new physics effects in the fully differential phase space, by enabling experiments to perform such studies on fully simulated Monte Carlo datasets via efficient event reweighing. As an example, we explore a class of new physics interactions that can fit the observed R(D(∗)) ratios, and show that analyses including more differential kinematic information can provide greater discriminating power for new physics, than single kinematic variables alone.

Ultraviolet completions for axionlike particles (ALPs) lighter than the neutral pion generically induce ALP-neutral pion mixing and are therefore sensitive to direct constraints on the mixing angle. For ALPs below the pion mass, we demonstrate that strong and novel bounds on the ALP-pion mixing angle can be extracted from existing rare pion decay data, measured by the PIENU and PIBETA experiments.

The τ polarization in semileptonic B decays provides probes of new physics complementary to decay rate distributions of the three-body final state. Prior calculations for inclusive decays used a definition for the polarization axis that is different from the choice used in calculations (and the only measurement) for exclusive channels. To compare inclusive and exclusive predictions, we calculate the τ polarization in inclusive B→Xτν¯ using the same choice as in the exclusive decays, and construct a sum rule relating the inclusive τ polarization to a weighted sum of exclusive decay polarizations. We use this relation, experimental data, and theoretical predictions for the decays to the lightest charm or up-type hadrons to make predictions for excited channels.

Normalizing the recent LHCb measurement of Λb→Λcτν¯ to the standard model (SM) prediction for the Λb→Λcμν¯ rate, instead of a LEP measurement, provides a more consistent comparison with the SM prediction for the lepton flavor universality ratio R(Λc). This modestly increases R(Λc) compared to the quoted LHCb result, such that it no longer hints at a suppression compared to the SM, which would be hard to accommodate in new physics scenarios that enhance R(D(∗)). We point out that the fraction of excited states in inclusive semileptonic Λb decay may be significantly greater than the corresponding fraction in B decays. Possible implications are speculated upon.

Abstract: We consider a twin WIMP scenario whose twin sector contains a full dark copy of the SM hadrons, where the lightest twin particles are twin pions. By analogy to the standard WIMP paradigm, the dark matter (DM) freezes out through twin electroweak interactions, and annihilates into a dark shower of light twin hadrons. These are either stable or decay predominantly to standard model (SM) photons. We show that this ‘hadrosymmetric’ scenario can be consistent with all applicable astrophysical, cosmological and collider constraints. In order to decay the twin hadrons before the big-bang nucleosynthesis epoch, an additional portal between the SM and twin sector is required. In most cases we find this additional mediator is within reach of either the LHC or future intensity frontier experiments. Furthermore, we conduct simulations of the dark shower and consequent photon spectra. We find that fits of these spectra to the claimed galactic center gamma-ray excess seen by Fermi -LAT non-trivially coincide with regions of parameter space that both successfully generate the observed DM abundance and exhibit minimal fine-tuning.

We revisit the experimental and theoretical status of B→ρlν¯ and B→ωlν¯ decays. We perform a combined fit of averaged spectra from Belle and BABAR measurements with prior light-cone sum rule calculations in order to obtain more precise predictions over the full q2 range. The extracted values of |Vub| from these combined fits exhibit smaller uncertainty compared to previous extractions from B→ρlν¯ and B→ωlν¯ decays, and the central values are found to be smaller than values extracted from B→πlν¯ or inclusive measurements. We use our fit results to obtain more precise predictions in and beyond the Standard Model for the lepton universality ratios R(ρ) and R(ω), as well as several angular observables that are sensitive to the full q2 distribution, such as the longitudinal polarization of the vector meson, the τ polarization, and its forward-backward asymmetry.

Very high multiplicity, spherically-symmetric distributions of soft particles, with pT ∼ few×100 MeV, may be a signature of strongly-coupled hidden valleys that exhibit long, efficient showering windows. With traditional triggers, such ‘soft bomb’ events closely resemble pile-up and are therefore only recorded with minimum bias triggers at a very low efficiency. We demonstrate a proof-of-concept for a high-level triggering strategy that efficiently separates soft bombs from pile-up by searching for a ‘belt of fire’: a high density band of hits on the innermost layer of the tracker. Seeding our proposed high-level trigger with existing jet, missing transverse energy or lepton hardware-level triggers, we show that net trigger efficiencies of order 10% are possible for bombs of mass several × 100 GeV. We also consider the special case that soft bombs are the result of an exotic decay of the 125 GeV Higgs. The fiducial rate for ‘Higgs bombs’ triggered in this manner is marginally higher than the rate achievable by triggering directly on a hard muon from associated Higgs production.