Impact of a XENONnT Signal on LHC Dijet Searches

It is well-known that dark matter (DM) direct detection experiments and the LHC are complementary, since they probe physical processes occurring at different energy scales. And yet, there are aspects of this complementarity which are still not fully understood, or exploited. For example, what is the impact that the discovery of DM at XENONnT would have on present and future searches for DM in LHC final states involving a pair of hadronic jets? In this work we investigate the impact of a XENONnT signal on the interpretation of current dijet searches at the LHC, and on the prospects for dijet signal discovery at the High-Luminosity (HL) LHC in the framework of simplified models. Specifically, we focus on a general class of simplified models where DM can have spin 0, 1/2 or 1, and interacts with quarks through the exchange of a scalar, pseudo-scalar, vector, or pseudo-vector mediator. We find that exclusion limits on the mediator's mass and its coupling to quarks from dijet searches at the LHC are significantly affected by a signal at XENONnT, and that $\mathcal{O}(100)$ signal events at XENONnT would drastically narrow the region in the parameter space of simplified models where a dijet signal can be discovered at $5\sigma$ C.L. at the HL-LHC.Comment: 23 pages, 3 figures, 3 tables, version accepted by JHE

Killing the Straw Man: Does BICEP Prove Inflation at the GUT Scale?

The surprisingly large value of $r$, the ratio of power in tensor to scalar density perturbations in the CMB reported by the BICEP2 Collaboration, if confirmed, provides strong evidence for Inflation at the GUT scale. While the Inflationary signal remains the best motivated source, a large value of $r$ alone would still allow for the possibility that a comparable gravitational wave background might result from a self ordering scalar field (SOSF) transition that takes place later at somewhat lower energy. We find that even without detailed considerations of the predicted BICEP signature of such a transition, simple existing limits on the isocurvature contribution to CMB anisotropies would definitively rule out a contribution of more than $5\%$ to $r \approx 0.2$,. We also present a general relation for the allowed fractional SOSF contribution to $r$ as a function of the ultimate measured value of $r$. These results point strongly not only to an inflationary origin of the BICEP2 signal, if confirmed, but also to the fact that if the GUT scale is of order $10^{16} GeV$ then either the GUT transition happens before Inflation or the Inflationary transition and the GUT transition must be one and the same.Comment: 3 pages 2 figures, accepted for publication in Physics Letters B . Accepted version revised slightly in response to referee's comment

Minimal Asymmetric Dark Matter

In the early Universe, any particle carrying a conserved quantum number and in chemical equilibrium with the thermal bath will unavoidably inherit a particle-antiparticle asymmetry. A new particle of this type, if stable, would represent a candidate for asymmetric dark matter (DM) with an asymmetry directly related to the baryon asymmetry. We study this possibility for a minimal DM sector constituted by just one (generic) $SU(2)_L$ multiplet $\chi$ carrying hypercharge, assuming that at temperatures above the electroweak phase transition an effective operator enforces chemical equilibrium between $\chi$ and the Higgs boson. We argue that limits from DM direct detection searches severely constrain this scenario, leaving as the only possibilities scalar or fermion multiplets with hypercharge $y = 1$, preferentially quintuplets or larger $SU(2)$ representations, and with a mass in the few TeV range.Comment: 9 pages, 2 figures, included t-channel scattering, added details on charged-neutral mass splitting and indirect detection, accepted in PL

Higher Dimensional Effective Operators for Direct Dark Matter Detection

We discuss higher dimensional effective operators describing interactions between fermionic dark matter and Standard Model particles. They are typically suppressed compared to the leading order effective operators, which can explain why no conclusive direct dark matter detection has been made so far. The ultraviolet completions of the effective operators, which we systematically study, require new particles. These particles can potentially have masses at the TeV scale and can therefore be phenomenologically interesting for LHC physics. We demonstrate that the lowest order options require Higgs-portal interactions generated by dimension six operators. We list all possible tree-level completions with extra fermions and scalars, and we discuss the LHC phenomenology of a specific example with extra heavy fermion doublets.Comment: 27 pages, 11 figures, 3 table

The 'anti-economics' of the European common market

I would like to preface my comments by extending a personal but public note of appreciation to the administrators, faculty and students of the Royal University for inviting me to visit and address this distinguished audience of scholars, business men and government officers, this evening on the theme of the 'Anti-Economics' of the European Common Market and its relation to the tax harmonization program of the Community. Perhaps the title of my talk warrants clarification? What is precisely meant by the 'anti-economics' of the European Economic Community for one; and what is meant by 'tax harmonization' for the other? And even more important, why should this distinguished gathering be interested in either one of them?peer-reviewe

Determining Dark Matter properties with a XENONnT/LZ signal and LHC-Run3 mono-jet searches

We develop a method to forecast the outcome of the LHC Run 3 based on the hypothetical detection of $\mathcal{O}(100)$ signal events at XENONnT. Our method relies on a systematic classification of renormalisable single-mediator models for dark matter-quark interactions, and is valid for dark matter candidates of spin less than or equal to one. Applying our method to simulated data, we find that at the end of the LHC Run 3 only two mutually exclusive scenarios would be compatible with the detection of $\mathcal{O}(100)$ signal events at XENONnT. In a first scenario, the energy distribution of the signal events is featureless, as for canonical spin-independent interactions. In this case, if a mono-jet signal is detected at the LHC, dark matter must have spin 1/2 and interact with nucleons through a unique velocity-dependent operator. If a mono-jet signal is not detected, dark matter interacts with nucleons through canonical spin-independent interactions. In a second scenario, the spectral distribution of the signal events exhibits a bump at non zero recoil energies. In this second case, a mono-jet signal can be detected at the LHC Run 3, dark matter must have spin 1/2 and interact with nucleons through a unique momentum-dependent operator. We therefore conclude that the observation of $\mathcal{O}(100)$ signal events at XENONnT combined with the detection, or the lack of detection, of a mono-jet signal at the LHC Run 3 would significantly narrow the range of possible dark matter-nucleon interactions. As we argued above, it can also provide key information on the dark matter particle spin.Comment: 17 pages, 8 figures, updated operator coefficients and figures, version accepted by PR