We present a formulation of naturalness made in the framework of Bayesian statistics, which unravels the conceptual problems related to previous approaches. Among other things, the relative ...interpretation of the measure of naturalness turns out to be unambiguously established by Jeffreys' scale. Also, the usual sensitivity formulation (the so-called Barbieri-Giudice measure) appears to be embedded in our formulation under an extended form. We derive the general sensitivity formula applicable to an arbitrary number of observables. Several consequences and developments are further discussed. As a final illustration, we work out the map of combined fine-tuning associated with the gauge hierarchy problem and neutralino dark matter in a classic supersymmetric model.
A
bstract
The existence of an axion-like particle (ALP) would induce anomalous scattering of light by light. This process can be probed at the Large Hadron Collider in central exclusive production of ...photon pairs in proton-proton collisions by tagging the surviving protons using forward proton detectors. Using a detailed simulation, we estimate the expected bounds on the ALP-photon coupling for a wide range of masses. We show that the proposed search is competitive and complementary to other collider bounds for masses above 600 GeV, especially for resonant ALP production between 600 GeV and 2 TeV. Our results are also valid for a CP-even scalar, and the efficiency of the search is independent of the width of the ALP.
We consider the possibility that the diphoton excess at 750 GeV is caused by a new scalar resonance produced in photon fusion. This scenario is parametrized by only one relevant effective couplings ...and is thus minimal. We show that this setup can reproduce both the production rate and width of the resonance, and is not in conflict with the 8 TeV limits on the diphoton cross section. The scenario also predicts event rates for WW, ZZ, Zgamma final states. We suggest for one to perform precision measurements by studying light-by-light scattering with intact protons detected in forward detectors. We construct a simple model that shows that the required couplings can be achieved with new vectorlike, uncolored fermions (with a strong Yukawa coupling to the resonance) which may also account for the required width.
A slight excess has been observed in the first data of photon-photon events at the 13 TeV Large Hadron Collider that might be interpreted as a hint of physics beyond the standard model. We show that ...a completely model-independent measurement of the photon-photon coupling of a putative 750 GeV resonance is possible using the forward proton detectors scheduled at ATLAS and CMS.
A
bstract
The sensitivities to the anomalous quartic gauge boson coupling
γγγZ
are estimated via
γZ
production with intact protons in the forward region at the LHC. Proton tagging proves to be a ...powerful tool to suppress the background, which allows consideration of the hadronic decays of the
Z
boson in addition to the leptonic ones. We discuss the discovery potential for an integrated luminosity of 300 fb
−1
and 3000 fb
−1
. The sensitivity we obtain at 300 fb
−1
goes beyond the one expected from LHC bounds on the
Z
→
γγγ
decay by about three orders of magnitude. The
γZ
channel provides important discriminatory information with respect to the exclusive
γγ
channel, as many particles beyond the Standard Model (such as a radion or Kaluza Klein gravitons) predict a signal in the latter but not the former.
The sensitivities to anomalous quartic photon couplings at the Large Hadron Collider are estimated using diphoton production via photon fusion. The tagging of the protons proves to be a very powerful ...tool to suppress the background and unprecedented sensitivities down to 7 x 10 super(-15) GeV-4 are obtained, providing a new window on extra dimensions and strongly interacting composite states in the multi-TeV range. Generic contributions to quartic photon couplings from charged and neutral particles with arbitrary spin are also presented.
We point out that the hypothesis of an SU(5)-like supersymmetric Grand Unified Theory (GUT) implies a generic relation within the flavour structure of up-type squarks. Contrary to other well-known ...SU(5) relations between the down-quark and charged lepton sectors, this relation remains exact in the presence of any corrections and extra operators. Moreover it remains valid to a good precision at the electroweak scale, and opens thus new possibilities for testing SU(5)-like GUTs. We derive the low-energy effective theory of observable light up-type squarks, that also constitutes a useful tool for squark phenomenology. We use this effective theory to determine how to test SU(5) relations at the LHC. Focusing on scenarios with light stops, compatible with Natural SUSY, it appears that simple tests involving ratios of event rates are sufficient to test the hypothesis of an SU(5)-like GUT theory. The techniques of charm-tagging and top-polarimetry are a crucial ingredient of these tests.
A
bstract
We study supersymmetric models with a GUT-sized extra dimension, where both the Higgs fields and the SUSY breaking hidden sector are localized on a 4D brane. Exponential wave function ...profiles of the matter fields give rise to hierarchical structures in the Yukawa couplings and soft terms. Such structures can naturally explain hierarchical fermion masses and mixings, while at the same time alleviating the supersymmetric flavour problem. We discuss two sources of supersymmetry breaking, radion mediation and brane fields, and perform a detailed numerical analysis, thoroughly taking into account the proliferation of unknown
(1) coefficients that occurs in this class of models. It turns out that additional assumptions on supersymmetry breaking are necessary to evade the stringent experimental bounds on lepton flavour violation. The favourable regions of parameter space are then examined with regards to their LHC phenomenology. They generically feature heavy gluinos and squarks beyond current bounds. Lepton flavour violation in SUSY cascade decays can give interesting signatures.
A
bstract
We investigate the possibilities of New Physics affecting the Standard Model (SM) Higgs sector. An effective Lagrangian with dimension-six operators is used to capture the effect of New ...Physics. We carry out a global Bayesian inference analysis, considering the recent LHC data set including all available correlations, as well as results from Tevatron. Trilinear gauge boson couplings and electroweak precision observables are also taken into account. The case of weak bosons tensorial couplings is closely examined and NLO QCD corrections are taken into account in the deviations we predict. We consider two scenarios, one where the coefficients of all the dimension-six operators are essentially unconstrained, and one where a certain subset is loop suppressed. In both scenarios, we find that large deviations from some of the SM Higgs couplings can still be present, assuming New Physics arising at 3 TeV. In particular, we find that a significantly reduced coupling of the Higgs to the top quark is possible and slightly favored by searches on Higgs production in association with top quark pairs. The total width of the Higgs boson is only weakly constrained and can vary between 0.7 and 2.7 times the Standard Model value within 95% Bayesian credible interval (BCI). We also observe sizeable effects induced by New Physics contributions to tensorial couplings. In particular, the Higgs boson decay width into
Zγ
can be enhanced by up to a factor 12 within 95% BCI.
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