A Heavy "Neutralino" in Warped Extra dimensions

Generic extensions of the Standard Model that respect baryon and lepton numbers have accidentally stable particles. Typical examples are the lightest exotic neutral fermion, or "neutralino", and fields with non-trivial lepton and baryon charges. In this paper we show that an accidentally stable neutralino is a natural dark matter candidate in models with warped extra dimensions. We find that annihilation into other Kaluza-Klein resonances is often allowed and very efficient. The observed dark matter abundance may then be obtained with couplings of order unity and a compactification scale above the TeV. Light dark matter is also possible in the presence of unsuppressed couplings to the Higgs boson. In this latter case direct detection experiments will soon be able to probe a significant portion of the parameter space.Comment: 17 pages (JHEP style) plus Appendice

Is entanglement observer-dependent?

The properties of quantum entanglement are examined and the role of the observer is pointed out.Comment: Latex, 5 pages, 1 fil

A dangerous irrelevant UV-completion of the composite Higgs

One of the most challenging hurdles to the construction of realistic composite Higgs models is the generation of Yukawa couplings for the Standard Model fermions. This problem can be successfully addressed in approximate conformal theories that admit a marginally relevant mixing between composite fermionic operators and the SM fermions. I argue that SU(3) gauge theories with light Dirac flavors in the fundamental representation feature all the ingredients under theoretical control, including a strongly-coupled IR fixed point, composite partners for all Standard Model fermions, absence of Landau poles at low energy, and a realistic phenomenology. These models acquire the status of compelling UV-completions of the SM if some spin-1/2 baryon operator has scaling dimension close to 2.5 within the conformal window, a possibility that can only be assessed via non-perturbative methods like lattice QCD. A distinctive collider signature is long-lived hadrons with fractional charges. Vacuum alignment is controlled by the Nambu-Goldstone bosons of the coset SU(4)xSU(4)/SU(4). With a technically natural choice of mixing for the top-quark, the exotic scalars with electro-weak charges acquire large positive masses and a compelling custodial-symmetric phenomenology is obtained. In the decoupling limit the symmetry breaking pattern effectively reduces to SU(4)->Sp(4) with a light Higgs.Comment: 14 pages, JHEP style, added discussion of vacuum alignment (first presented at https://lattice.llnl.gov/meetings/2015/beyond-standard-model-physics/presentations/2015-04-24/1630_VECCHI.pdf

WIMPs and Un-Naturalness

The WIMP "miracle" suggests a new physics threshold ranging from the weak scale up to several tens of TeVs. Obtaining the correct dark matter density in many theories aiming to solve the hierarchy problem may thus require some amount of tuning of the weak scale, hinting at a possible connection between WIMP dark matter and unnaturalness. We point out that dark matter direct detection is a very efficient probe of these unnatural models, and that existing data already provide important clues to the nature of the associated WIMPs. We present a model-independent, relativistic analysis of the signatures of a gauge-singlet dark matter candidate of arbitrary spin, and discuss the current experimental bounds from LUX and XENON100. For complex WIMPs, dark matter direct detection is complementary to electroweak precision tests, and can even compete with flavor constraints if the dark matter has spin. Particularly relevant for future searches are couplings to the Higgs mass operator, which are expected to be large if the electroweak scale is finely tuned. Care is devoted to the RG evolution of the effective Lagrangian. We find that the CP-even scalar coupling to charm quarks is enhanced by about 20% compared to the one-loop estimate. When pushed in the unnatural regime, warped extra dimensions -- with or without custodial symmetry -- become attractive theories for flavor, the Higgs mass, and dark matter. The WIMP argument basically sets an upper bound on unnaturalness, whereas direct detection experiments select scalar or real particles as the most compelling dark matter candidates.Comment: 25 pages plus Appendix, 3 figures. V2: reference added, discussion on pNGB Higgs mass correcte

The Natural Composite Higgs

The discovery of the Higgs boson has put considerable pressure on theories that aim to solve the hierarchy problem. Scenarios in which the Higgs is a pseudo Nambu-Goldstone boson (NGB) of some new strong dynamics must possess a number of non-generic features in order to pass the progressively stringent collider bounds and simultaneously meet our naturalness criteria. Among these features are the existence of light fermionic partners of the top quark and an efficient collective breaking of the Nambu-Goldstone symmetry. The top partners have to be not only parametrically lighter than the other composites, but also weakly coupled to them in order to suppress unwanted flavor-violating effects. A Natural pseudo-NGB Higgs model should also be able to fit the LHC Higgs data without fine-tuning. Among theories with comparable compositeness scales, those that predict smaller corrections in the Higgs couplings to the standard model particles are therefore preferred. A concrete implementation of these ingredients is discussed in a scenario based on the coset SU(5)/SO(5). The fit to the current LHC Higgs data is significantly improved compared to the minimal scenarios, and a fully natural explanation of both the weak scale and the Higgs boson mass can be attained. An important role is played by an independent quartic Higgs coupling generated by UV-sensitive loops involving electroweak doublets mixing with the top partners. The collider signature of this framework is shown to be rather model-dependent; in particular, the exotic scalars can alter the phenomenology of the top partners at a qualitative level.Comment: 41 pages plus Appendix (JHEP style), 8 figures. Version 2: references added/corrected, minor changes (results unchanged

Hidden assumptions in decoherence theory

The role of implicit assumptions in current decoherence theory is pointed out and clarified.Comment: Te

ANTARES: Status, first results and multi-messenger astronomy

The ANTARES Collaboration has completed in 2008 the deployment of what is currently the largest high energy neutrino detector in the Northern hemisphere. The search for cosmic neutrinos in the energy range between tens of GeV and tens of PeV is performed by means of a three dimensional array of photomultiplier tubes (PMTs), arranged on 12 vertical structures (strings) located in the Mediterranean Sea at a depth of about 2500 meters. The detection principle relies on the identification of the Cherenkov light produced as ultra-relativistic muons propagate in water. The main goal of the detector is the search for point-like sources of cosmic neutrinos from both Galactic and extra-Galactic sources. Besides the search for point sources, other analysis topics are strongly pursued and will be described in the following.Comment: Proceedings of Rencontres de Moriond (EW session) La Thuile, Italy, March 201

Are classical probabilities instances of quantum amplitudes?

A conjecture about the quantum nature of classical probabilites is set forth and discussed.Comment: Latex, 7 page

The anomalous dimension of spin-1/2 baryons in many flavors QCD

The anomalous dimension of spin-1/2 baryon operators in QCD is derived at leading 1/Nf order using the minimal subtraction scheme. A residual ambiguity, originating from the presence of evanescent operators in dimensional regularization, is parametrized by a function of the renormalized coupling. Our result is shown to agree with previous 2 and 3 loop calculations performed in two different renormalization schemes.Comment: We briefly discuss the absence of scheme-dependence in physical observables to all orders in \alpha Nf and comment on the value of the anomalous dimension within the conformal windo

Shannon entropy and blackbody radiation

A response to criticism of the author's previous paper quant-ph/0002084.Comment: Latex, 3 page