Naturalness after LHC8

I review the status of naturalness of the weak scale after the results from the LHC operating at an energy of 8 TeV. Talk delivered at the 2013 Europhysics Conference on High Energy Physics (EPS), Stockholm, Sweden, 18-24 July 2013.Comment: 13 pages, 1 figure; 2013 EPS Conference Proceeding

Recent Developments in Physics Beyond the Standard Model

In this talk I discuss some recent developments in physics beyond the Standard Model. After some initial comments on neutrino masses, I discuss the status of low-energy supersymmetry and finally turn to describing some recent work in theories with extra spatial dimensions. Plenary talk at the XIX International Symposium on Lepton and Photon Interactions at High Energies, Stanford University, 9-14 August 1999.Comment: 25 pages, 2 eps figure

A new ansatz for quark and lepton mass matrices

A new ansatz for quark and lepton mass matrices is proposed in the context of supersymmetric grand unified theories. The 13 parameters describing fermion masses and mixings are determined in terms of only 6 free parameters, allowing 7 testable predictions. The values of $V_{us}$, $V_{cb}$, $V_{ub}$, $m_u$, $m_d$, $m_s$, and $m_b$ are then predicted as a function of the 3 charged lepton masses, $m_c$, $m_t$, and $\tan \beta$, the ratio of Higgs vacuum expectation values. In particular the Cabibbo angle and $m_s/m_d$ are determined in terms of only lepton masses. All predictions are in very good agreement with experiments.Comment: 10 page

Beyond the Standard Model

Elementary introduction to physics beyond the Standard Model. Lectures delivered at the 1995 European School of High-Energy Physics in Dubna, Russia.Comment: 19 page

On the Tuning Condition of Split Supersymmetry

Split Supersymmetry does not attempt to solve the hierarchy problem, but it assumes a tuning condition for the electroweak scale. We clarify the meaning of this condition and show how it is related to the underlying parameters. Simple assumptions on the structure of the soft terms lead to predictions on tan beta and on the physical Higgs mass.Comment: 9 pages, 6 figures, latex2

KK Gravitons and Unitarity Violation in the Randall-Sundrum Model

We show that perturbative unitarity for $W_LW_L$ scattering places significant constraints on the Randall-Sundrum theory with two 3-branes, with matter confined to the TeV brane. The exchange of massive 4D Kaluza-Klein gravitons leads to amplitudes growing linearly with the CM energy squared. Summing over KK gravitons up to a scale \lbar and testing unitarity at \sqrt s=\lbar, one finds that unitarity is violated for \lbar below the 'naive dimensional analysis' scale, $\Lambda_{NDA}$. We evaluate \lbar as a function of the curvature ratio $m_0/M_{Planck}$ for the pure gravity theory. We then demonstrate that unitarity need not be violated at \lbar in the presence of a heavy Higgs boson. In fact, much larger Higgs masses are consistent with unitarity than if no KK gravitons are present. Observation of the mass and width (or cross section) of one or more KK gravitons at the LHC will directly determine $m_0/M_{Planck}$ and the scale $\hat \Lambda$ specifying the couplings of matter to the KK gravitons. With this information in hand and a measurement of the Higgs boson mass, one can determine the precise scale \lbar below which unitarity will remain valid.Comment: 14 pages, 8 figures, major revisions mad

Two Color Matter in the Quenched Approximation

We study a quenched SU(2) lattice gauge theory in 4d in which the spatial gauge ensemble $\{U_i\}$ is generated from a 3d gauge-Higgs model and the timelike link variables are ``reconstructed'' from the Higgs fields. The resulting ensemble is used to study quenched quark propagation with non-zero chemical potential $\mu$. While it proves possible to alter the strength of the inter-quark interaction by changing the parameters of the dimensionally reduced model, there is no evidence for any region of parameter space where quarks exhibit deconfined behaviour or thermodynamic observables scale as if there were a Fermi surface.Comment: 7 pages, 4 figures; Poster presented at the XXV International Symposium on Lattice Field Theory, July 30 - August 4 2007, Regensburg, German