Light Signals from a Lighter Higgs

With the Higgs search program already quite mature, there is the exciting possibility of discovering a new particle with rates near that of the SM Higgs. We consider models with a signal in $\gamma \gamma$ below the SM Higgs mass, taking the recent $2.9\, \sigma$ (local) CMS excess at 95 GeV as a target. We discuss singlet models with additional vectorlike matter, but argue that a Type-I two Higgs doublet model provides a more economical scenario. In such a setup, going into regions of moderate-to-strong fermiophobia, the enhanced $\gamma \gamma$ branching ratio allows signals from $VH$+VBF production to yield $\sigma \times BR_{\gamma\gamma}$ comparable to total SM rates. Light $H$ production can be dominated via rare top decays $t \rightarrow b H^+ \rightarrow b W^{*} H$, which provides an alternate explanation of the excess. We consider this in the context of other Higgs anomalies, namely the LEP Higgs excess near the same mass, and excesses in $t\bar{t}h$ searches at Tevatron and LHC. We find that with $140\, \mathrm{GeV} < m_{H^+} < 160\, \mathrm{GeV}$, $\tan \beta \sim 5$ and a coupling to gauge bosons of $\sin^2 \delta \sim 0.1$, such a scenario can produce all the excesses simultanously, where $tth$ arise from contamination from the rare top decays, as previously proposed. An implication of the Type-I scenario is that any $\gamma \gamma$ excess should be associated with additional elements that could reduce background, including $b$-jets, forward jets or signs of vector boson production.Comment: 15 pages, 3 figure

Quark and lepton masses from top loops

Assuming that the leptons and quarks other than top are massless at tree level, we show that their masses may be induced by loops involving the top quark. As a result, the generic features of the fermion mass spectrum arise from combinations of loop factors. Explicitly, we construct a renormalizable model involving a few new particles, which leads to 1-loop bottom and tau masses, a 2-loop charm mass, 3-loop muon and strange masses, and 4-loop masses for first generation fermions. This realistic pattern of masses does not require any symmetry to differentiate the three generations of fermions. The new particles may produce observable effects in future experiments searching for mu to e conversion in nuclei, rare meson decays, and other processes.Comment: 29 pages; Introduction expanded, references adde

Exotic Decays of Heavy B quarks

Heavy vector-like quarks of charge $-1/3$, $B$, have been searched for at the LHC through the decays $B\rightarrow bZ,\, bh,\,tW$. In models where the $B$ quark also carries charge under a new gauge group, new decay channels may dominate. We focus on the case where the $B$ is charged under a $U(1)^\prime$ and describe simple models where the dominant decay mode is $B\rightarrow bZ^\prime\rightarrow b (b\bar{b})$. With the inclusion of dark matter such models can explain the excess of gamma rays from the Galactic center. We develop a search strategy for this decay chain and estimate that with integrated luminosity of 300 fb$^{-1}$ the LHC will have the potential to discover both the $B$ and the $Z'$ for $B$ quarks with mass below $\sim 1.6$ TeV, for a broad range of $Z'$ masses. A high-luminosity run can extend this reach to $2$ TeV.Comment: 28 pages, 10 figures, 3 table

Catastrophic Decays of Compactified Space-Times

Witten long ago pointed out that the simplest Kaluza-Klein theory, without supersymmetry, is subject to a catastrophic instability. There are a variety of string theories which are potentially subject to these instabilities. Here we explore a number of questions: how generic are these instabilities? what happens when a potential is generated on the moduli space? in the presence of supersymmetry breaking, is there still a distinction between supersymmetric and non-supersymmetric states?Comment: Typos corrected, references adde