Twin Peak Higgs

A broad class of models in which electroweak symmetry breaking originates from dynamics in a singlet dark sector, and is transferred to the Standard Model via the Higgs portal, predicts in general strongly suppressed Higgs boson mixing with a singlet scalar. In this work we point out that at present this class of models allows for the second phenomenologically acceptable solution with almost maximal mixing between the Higgs and the scalar singlet. This scenario predicts an almost degenerate twin peak Higgs signal which is presently indistinguishable from a single peak, due to the limited LHC mass resolution. Because of that, the LHC experiments measure inclusive Higgs rates that all must exactly agree with Standard Model predictions due to sum rules. We show that if the dark sector and Standard Model communicate only via the singlet messenger scalar that mixes with the Higgs, the spin independent direct detection cross section of dark matter is suppressed by the scalar mass degeneracy, explaining its non-observation so far.Comment: 6 pages, 3 figures, 1 table. Final version to be published in Physics Letters

Equilibrium ion distribution in the presence of clearing electrodes and its influence on electron dynamics

Here we compute the ion distribution produced by an electron beam when ion-clearing electrodes are installed. This ion density is established as an equilibrium between gas ionization and ion clearing. The transverse ion distributions are shown to strongly peak in the beam's center, producing very nonlinear forces on the electron beam. We will analyze perturbations to the beam properties by these nonlinear fields. To obtain reasonable simulation speeds, we develop fast algorithms that take advantage of adiabatic invariants and scaling properties of Maxwell's equations and the Lorentz force. Our results are very relevant for high current Energy Recovery Linacs, where ions are produced relatively quickly, and where clearing gaps in the electron beam cannot easily be used for ion elimination. The examples in this paper therefore use parameters of the Cornell Energy Recovery Linac project. For simplicity we only consider the case of a circular electron beam of changing diameter. However, we parameterize this model to approximate non-round beams well. We find suitable places for clearing electrodes and compute the equilibrium ion density and its effect on electron-emittance growth and halo development. We find that it is not sufficient to place clearing electrodes only at the minimum of the electron beam potential where ions are accumulated

Anomalous Higgs-boson coupling effects in HWW production at the LHC

We study the LHC associated production of a Higgs boson and a W^+W^- vector-boson pair at 14 TeV, in the Standard Model and beyond. We consider different signatures corresponding to the cleanest H and W decay channels, and discuss the potential of the high-luminosity phase of the LHC. In particular, we investigate the sensitivity of the HWW production to possible anomalous Higgs couplings to vector bosons and fermions. Since the b-quark initiated partonic channel contributes significantly to this process, we find a moderate sensitivity to both the size and sign of an anomalous top-quark Yukawa coupling, because perturbative unitarity in the standard model implies a destructive interference in the b b-bar subprocess. We show that a combination of various signatures can reach a ~9 standard-deviation sensitivity in the presently allowed negative region of the top-Higgs coupling, if not previously excluded.Comment: 13 pages, 3 figure

Minimal flavor-changing Z′Z' models and muon g−2g-2 after the RK∗R_{K^*} measurement

There has been a steady interest in flavor anomalies and their global fits as ideal probes of new physics. If the anomalies are real, one promising explanation is a new $Z'$ gauge boson with flavor-changing coupling to bottom and strange quarks and a flavor-conserving coupling to muons and, possibly, electrons. We point out that direct production of such a $Z'$, emerging from the collision of $b$ and $s$ quarks, may offer a complementary window into these phenomena because collider searches already provide competitive constraints. On top of that, we analyse the same $Z'$ scenario in relation to another long-standing discrepancy between theory and experiment that concerns the anomalous magnetic moment of the muon. By scanning the allowed $Z'$ coupling strengths in the low-mass region, we assess the compatibility of the signals from LHCb with the $Z'$ searches in the high energy LHC data and the measurements of the anomalous magnetic moment of the involved leptons. We also argue that observations of the latter can break the degeneracy pattern in the Wilson coefficients $C_9$ and $C_{10}$ presented by LHCb data. The $Z'$ model we consider is compatible with the new measurement of $R_{K^*}$, therefore it can potentially account for the long-standing deviations observed in $B$-physics.Comment: 13 pages, 5 figures. Missing factors corrected in eqs. 2.7-2.9 with slight updates in fig.

Towards Completing the Standard Model: Vacuum Stability, EWSB and Dark Matter

We study the standard model (SM) in its full perturbative validity range between $\Lambda_QCD$ and the $U(1)_Y$ Landau pole, assuming that a yet unknown gravitational theory in the UV does not introduce additional particle thresholds, as suggested by the tiny cosmological constant and the absence of new stabilising physics at the EW scale. We find that, due to dimensional transmutation, the SM Higgs potential has a global minimum at 10^26 GeV, invalidating the SM as a phenomenologically acceptable model in this energy range. We show that extending the classically scale invariant SM with one complex singlet scalar S allows us to: (i) stabilise the SM Higgs potential; (ii) induce a scale in the singlet sector via dimensional transmutation that generates the negative SM Higgs mass term via the Higgs portal; (iii) provide a stable CP-odd singlet as the thermal relic dark matter due to CP-conservation of the scalar potential; (iv) provide a degree of freedom that can act as an inflaton in the form of the CP-even singlet. The logarithmic behaviour of dimensional transmutation allows one to accommodate the large hierarchy between the electroweak scale and the Landau pole, while understanding the latter requires a new non-perturbative view on the SM.Comment: 15 pages, 9 figures. Final version to be published in Physical Review

The EDGES 21 cm Anomaly and Properties of Dark Matter

The recently claimed anomaly in the measurement of the 21 cm hydrogen absorption signal by EDGES at $z\sim 17$, if cosmological, requires the existence of new physics. The possible attempts to resolve the anomaly rely on either (i) cooling the hydrogen gas via new dark matter-hydrogen interactions or (ii) modifying the soft photon background beyond the standard CMB one, as possibly suggested also by the ARCADE~2 excess. We argue that solutions belonging to the first class are generally in tension with cosmological dark matter probes once simple dark sector models are considered. Therefore, we propose soft photon emission by light dark matter as a natural solution to the 21 cm anomaly, studying a few realizations of this scenario. We find that the signal singles out a photophilic dark matter candidate characterised by an enhanced collective decay mechanism, such as axion mini-clusters.Comment: 7 pages, 2 figure