Mu to e gamma and matching at mW

Several experiments search for \mu - e flavour change, for instance in \mu ->e conversion, \mu-> e \gamma, and \mu -> 3e. This paper studies how to translate these experimental constraints from low energy to a New Physics scale M >> mW. A basis of QCD and QED-invariant operators (as appropriate below mW) is constructed, then run to mW with one-loop RGEs of QCD and QED. At mW, these operators are matched onto SU(2)-invariant dimension-six operators, which can continue to run up with electroweak RGEs. As an example, the \mu-> e \gamma bound is translated to the scale M, where it constrains two sums of operators. The constraints differ from those obtained in previous EFT analyses of \mu -> e \gamma, but reproduce the expected bounds on flavour-changing interactions of the Z and the Higgs, because the matching at mW is pragmatically performed to the loop order required to get the "leading" contribution.Comment: minor changes (typos corrected), version accepted for publicatio

Basis independent parametrisations of R parity violation in the soft SUSY breaking sector

The magnitude of R-parity violating coupling constants depends on which direction in the space of weak doublets with hypercharge = -2 corresponds to the Higgs. To address this ``basis dependence'', one can construct combinations of coupling constants that are invariant under these basis transformations, and which parametrise how much R parity violation is present in the Lagrangian (analogous to Jarlskog invariants for CP violation). This has previously been done for the Higgs vev and the R parity violating couplings constants in the superpotential. In this letter, I build invariants that include soft SUSY breaking interactions, and briefly discuss their relation to invariants involving the Higgs vev. This completes the construction of invariants based on the MSSM with baryon parity.Comment: 8 pages, accepted for publication in PL

Axions: Bose Einstein Condensate or Classical Field?

The axion is a motivated dark matter candidate, so it would be interesting to find features in Large Scale Structures specific to axion dark matter. Such features were proposed for a Bose Einstein condensate of axions, leading to confusion in the literature (to which I contributed) about whether axions condense due to their gravitational interactions. This note argues that the Bose Einstein condensation of axions is a red herring: the axion dark matter produced by the misalignment mechanism is already a classical field, which has the distinctive features attributed to the axion condensate (BE condensates are described as classical fields). This note also estimates that the rate at which axion particles condense to the field, or the field evaporates to particles, is negligeable.Comment: 11 pages, 1 figure, version accepted for publicatio

Flavoured Leptogenesis

Thermal leptogenesis, in the seesaw model, is a popular mechanism for generating the Baryon Asymmetry of the Universe. It was noticed recently, that including lepton flavour can modify significantly the results. These proceedings aim to discuss why and when flavour matters, in the thermal leptogenesis scenario for hierarchical right-handed neutrinos. No Boltzmann Equations are introduced.Comment: 15 pages, 2 figures, proceedings for the Venice Neutrino Telescopes Conference. Some typos corrected and references adde

Including the Z in an Effective Field Theory for dark matter at the LHC

An Effective Field Theory for dark matter at a TeV-scale hadron collider should include contact interactions of dark matter with the partons, the Higgs and the Z. This note estimates the impact of including dark matter-Z interactions on the complementarity of spin dependent direct detection and LHC monojet searches for dark matter. Their effect is small, because they are suppressed by electroweak couplings and the contact interaction self-consistency condition $C/\Lambda^2 < 4\pi/\hat{s}$. In this note, the contact interactions between the Z and dark matter are parametrised by derivative operators; this is convenient at colliders because such interactions do not match onto the quark-dark matter contact interactions.Comment: 8 pages, 3 figures, version accepted for publication (same content, presentation hopefully improved

Determining See-Saw Parameters from Weak Scale Measurements?

The see-saw mechanism is a very attractive explanation for small neutrino masses, parametrized at the GUT scale by the right-handed Majorana mass matrix, ${\cal M}$, and the neutrino Yukawa matrix, ${\bf Y_\nu}$. We show that in a SUSY model with universal soft terms, ${\cal M}$ and ${\bf Y_\nu}$ can be calculated from the light neutrino masses, the MNS matrix, and ${\bf Y^{\dagger}_\nu} {\bf Y_\nu}$, which enters into the left-handed slepton radiative corrections. This suggests that in principle the GUT-scale inputs of the seesaw could be reconstructed from the neutrino and sneutrino mass matrices. We briefly discuss why this is impractical, but advocate the neutrino and sneutrino mass matrices as an alternative bottom-up parametrization of the seesaw.Comment: Version to be published. References added, modified abstract, minor stylistic changes. Content unchange

Non standard neutrino interactions at LEP2 and the LHC

We consider Non-Standard neutrino Interactions (NSI) connecting two neutrinos with two first-generation fermions ($e, u$ or $d$), which we assume to arise at at dimension eight due to New Physics. The coefficient is normalised as $4 \epsilon G_F/\sqrt{2}$. We explore signatures of NSI-on-electrons at LEP2, and of NSI-on-quarks at the LHC, treating the NSI as contact interactions at both energies. In models where the coefficients of dangerous dimension six operators are suppressed by cancellations, LEP2 provides interesting bounds on NSI operators (\epsilon \lsim 10^{-2} - 10^{-3}), which arise because $\sqrt{s} \sim 200$ GeV, and the cancellation applied at zero momentum transfer. At the LHC, we use the Equivalence Theorem, which relates the longitudinal $W$ to the Higgs, to estimate the rate for $\bar{q} q W^+W^- e_\alpha^+ e_\beta^-$ induced by NSI. We find that the cross-section is small, but that the outgoing particles have very high $p_T > 400$ GeV, which reduces the issue of backgrounds. In a conservative scenario, we find that the LHC at 14 TeV and with 100 fb$^{-1}$ of data would have a sensitivity to \epsilon \gsim 3 \times 10^{-3}.Comment: 4 pages, contribution to NUFACT 11, XIIIth International Workshop on Neutrino Factories, Super beams and Beta beams, 1-6 August 2011, CERN and University of Geneva (Submitted to IOP conference series

Thermalisation after inflation

During (re)heating of the universe after inflation, the relativistic decay products of the inflaton field $\phi$ must lose energy and additional particles must be produced to attain a thermalised state at a temperature T_{\reh}. We estimate the rate of energy loss via elastic and inelastic scattering interactions. Elastic scattering is an inefficient energy loss mechanism so inelastic processes, although higher order in the coupling $\alpha$, can be faster because more energy is transfered. The timescale to produce a particle number density of {\cal O}(T_{\reh}^3) is the inelastic energy loss timescale, \sim(\alpha^3 n_\phi/T_{\reh}^2)^{-1}.Comment: minor changes: another reference, additional sentences in introduction. Version accepted by journa