## Journal Club

Seminar Room, Mondays at 14:00

### Monday 14th of December, 2015

# Tensor Networks from Kinematic Space

(Submitted on 4 Dec 2015)

We point out that the MERA network for the ground state of a 1+1-dimensional conformal field theory has the same structural features as kinematic space---the geometry of CFT intervals. In holographic theories kinematic space becomes identified with the space of bulk geodesics studied in integral geometry. We argue that in these settings MERA is best viewed as a discretization of the space of bulk geodesics rather than of the bulk geometry itself. As a test of this kinematic proposal, we compare the MERA representation of the thermofield-double state with the space of geodesics in the two-sided BTZ geometry, obtaining a detailed agreement which includes the entwinement sector. We discuss how the kinematic proposal can be extended to excited states by generalizing MERA to a broader class of compression networks.

Presented by J. M. Lizana

#
One Leptoquark to Rule Them All: A Minimal Explanation for RD(∗) , RK and (g−2)μ

(Submitted on 5 Nov 2015)

We show that by adding a single new scalar particle to the Standard Model, a TeV-scale leptoquark with the quantum numbers of a right-handed down quark, one can explain in a natural way three of the most striking anomalies of particle physics: the violation of lepton universality inB¯→K¯ℓ+ℓ− decays, the enhancedB¯→D(∗)τν¯ decay rates, and the anomalous magnetic moment of the muon. Constraints from other precision measurements in the flavor sector can be satisfied without fine-tuning. Our model predicts enhancedB¯→K¯(∗)νν¯ decay rates and a new-physics contribution toBs−B¯s mixing close to the current central fit value.

Presented by R. Vega-Morales

# Z' models for the LHCb and g-2 muon anomalies

(Submitted on 23 Nov 2015)

We revisit a class of Z' explanations of the anomalies found by the LHCb collaboration inB decays, and show that the scenario is tightly constrained by a combination of constraints: (i) LHC searches for di-muon resonances, (ii) pertubativity of the Z' couplings; (iii) theBs mass difference, and (iv) and electro-weak precision data. Solutions are found by suppressing the Z' coupling to electrons and to light quarks and/or by allowing for a Z' decay width into dark matter. We also present a simplified framework where a TeV-scale Z' gauge boson that couples to standard leptons as well as to new heavy vector-like leptons, can simultaneously accommodate the LHCb anomalies and the muon g-2 anomaly.

Presented by R. Vega-Morales

# Creating the Fermion Mass Hierarchies with Multiple Higgs Bosons

(Submitted on 10 Dec 2015)

After the Higgs boson discovery, it is established that the Higgs mechanism explains electroweak symmetry breaking and generates the masses of all particles in the Standard Model, with the possible exception of neutrino masses. The hierarchies among fermion masses and mixing angles remain however unexplained. We propose a new class of two Higgs doublet models in which a flavor symmetry broken at the electroweak scale addresses this problem. The models are strongly constrained by electroweak precision tests and the fact that they produce modifications to Higgs couplings and flavor changing neutral currents; they are also constrained by collider searches for extra scalar bosons. The surviving models are very predictive, implying unavoidable new physics signals at the CERN Large Hadron Collider, e.g. extra Higgs Bosons with massesM<700 GeV.

Presented by J. Santiago