Discovering hidden sectors with mono-photon Z' searches

In many theories of physics beyond the Standard Model, from extra dimensions to Hidden Valleys and models of dark matter, Z' bosons mediate between Standard Model particles and hidden sector states. We study the feasibility of observing such hidden states through an invisibly decaying Z' at the LHC. We focus on the process pp -> \gamma Z' -> \gamma X X*, where X is any neutral, (quasi-) stable particle, whether a Standard Model (SM) neutrino or a new state. This complements a previous study using pp -> Z Z' -> l+ l- X X*. Only the Z' mass and two effective charges are needed to describe this process. If the Z' decays invisibly only to Standard Model neutrinos, then these charges are predicted by observation of the Z' through the Drell-Yan process, allowing discrimination between Z' decays to SM neutrinos and invisible decays to new states. We carefully discuss all backgrounds and systematic errors that affect this search. We find that hidden sector decays of a 1 TeV Z' can be observed at 5 sigma significance with 50 fb^{-1} at the LHC. Observation of a 1.5 TeV state requires super-LHC statistics of 1 ab^{-1}. Control of the systematic errors, in particular the parton distribution function uncertainty of the dominant Z \gamma background, is crucial to maximize the LHC searchComment: 13 pages, 4 figure

Two novel PCR-based assays for sexing of Silene latifolia and Silene dioica plants

Silene latifolia and S. dioica are model systems in studies of plant reproduction, chromosome evolution and sexual dimorphism, but sexing of plants based on morphology is only possible from flowering stage onwards. Both species show homogametic females (XX) and heterogametic males (XY). • Here we developed two assays (primer pairs ss816 and ss441) for molecular sexing of S. latifolia and S. dioica, targeting length polymorphisms between the X and Y-linked copies of the spermidine synthase gene. The two assays were successful in identifying known (flowering-stage) males and females from UK and Spanish populations, with an error rate of 3.1% (ss816; successful for both species) and 0% (ss441, only successful for S. latifolia). Our assays therefore represent novel tools for rapid, robust and simple determination of the genotypic sex of S. latifolia and S. dioica

Accidental Supersymmetric Dark Matter and Baryogenesis

We show that "accidental" supersymmetry is a beyond-the-Standard Model framework that naturally accommodates a thermal relic dark matter candidate and successful electroweak baryogenesis, including the needed strongly first-order character of the electroweak phase transition. We study the phenomenology of this setup from the standpoint of both dark matter and baryogenesis. For energies around the electroweak phase transition temperature, the low-energy effective theory is similar to the MSSM with light super-partners of the third-generation quarks and of the Higgs and gauge bosons. We calculate the dark matter relic abundance and the baryon asymmetry across the accidental supersymmetry parameter space, including resonant and non-resonant CP-violating sources. We find that there are regions of parameter space producing both the observed value of the baryon asymmetry and a dark matter candidate with the correct relic density and conforming to present-day constraints from dark matter searches. This scenario makes sharp predictions for the particle spectrum, predicting a lightest neutralino mass between 200 and 500 GeV, with all charginos and neutralinos within less than a factor 2 of the lightest neutralino mass and the heavy Higgs sector within 20-25% of that mass, making it an interesting target for collider searches. In addition, we demonstrate that successful accidental supersymmetric dark matter and baryogenesis will be conclusively tested with improvements smaller than one order of magnitude to the current performance of electron electric dipole moment searches and of direct dark matter searches, as well as with IceCube plus Deep Core neutrino telescope data.Comment: 36 pages, 10 figure

Z' signals in polarised top-antitop final states

We study the sensitivity of top-antitop samples produced at all energy stages of the Large Hadron Collider (LHC) to the nature of an underlying Z' boson, in presence of full tree level standard model (SM) background effects and relative interferences. We concentrate on differential mass spectra as well as both spatial and spin asymmetries thereby demonstrating that exploiting combinations of these observables will enable one to distinguish between sequential Z's and those pertaining to Left-Right symmetric models as well as E6 inspired ones, assuming realistic final state reconstruction efficiencies and error estimates.Comment: 21 pages, 6 colour figures, 10 table

Constraining the Littlest Higgs

Little Higgs models offer a new way to address the hierarchy problem, and give rise to a weakly-coupled Higgs sector. These theories predict the existence of new states which are necessary to cancel the quadratic divergences of the Standard Model. The simplest version of these models, the Littlest Higgs, is based on an $SU(5)/SO(5)$ non-linear sigma model and predicts that four new gauge bosons, a weak isosinglet quark, $t'$, with $Q=2/3$, as well as an isotriplet scalar field exist at the TeV scale. We consider the contributions of these new states to precision electroweak observables, and examine their production at the Tevatron. We thoroughly explore the parameter space of this model and find that small regions are allowed by the precision data where the model parameters take on their natural values. These regions are, however, excluded by the Tevatron data. Combined, the direct and indirect effects of these new states constrain the `decay constant' f\gsim 3.5 TeV and m_{t'}\gsim 7 TeV. These bounds imply that significant fine-tuning be present in order for this model to resolve the hierarchy problem.Comment: 31 pgs, 26 figures; bound on t' mass fixed to mt'>2f, conclusions unchange

Signals for Non-Commutative Interactions at Linear Colliders

Recent theoretical results have demonstrated that non-commutative geometries naturally appear within the context of string/M-theory. One consequence of this possibility is that QED takes on a non-abelian nature due to the introduction of 3- and 4-point functions. In addition, each QED vertex acquires a momentum dependent phase factor. We parameterize the effects of non-commutative space-time co-ordinates and show that they lead to observable signatures in several $2\to 2$ QED processes in $e^+e^-$ collisions. In particular, we examine pair annihilation, Moller and Bhabha scattering, as well as $\gamma\gamma\to\gamma\gamma$ scattering and show that non-commutative scales of order a TeV can be probed at high energy linear colliders.Comment: 51 pages, 23 figures, typos corrected, figure and references adde

Photon-Photon and Electron-Photon Colliders with Energies Below a TeV

We investigate the potential for detecting and studying Higgs bosons in $\gamma\gamma$ and $e\gamma$ collisions at future linear colliders with energies below a TeV. Our study incorporates realistic $\gamma\gamma$ spectra based on available laser technology, and NLC and CLIC acceleration techniques. Results include detector simulations. We study the cases of: a) a SM-like Higgs boson based on a devoted low energy machine with $\sqrt{s_{ee}}\le 200$ GeV; b) the heavy MSSM Higgs bosons; and c) charged Higgs bosons in $e\gamma$ collisions.We investigate the potential for detecting and studying Higgs bosons in $\gamma\gamma$ and $e\gamma$ collisions at future linear colliders with energies below a TeV. Our study incorporates realistic $\gamma\gamma$ spectra based on available laser technology, and NLC and CLIC acceleration techniques. Results include detector simulations. We study the cases of: a) a SM-like Higgs boson based on a devoted low energy machine with $\sqrt{s_{ee}}\le 200$ GeV; b) the heavy MSSM Higgs bosons; and c) charged Higgs bosons in $e\gamma$ collisions

Dusty MgII absorbers: population statistics, extinction curves and gamma-ray burst sightlines

We present a new determination of the dust content and near-ultraviolet/optical extinction curves associated with a sample of ~8300 strong (equivalent width > 1A) Mg II absorbers, with redshifts 0.4<z<2.2, identified in Sloan Digital Sky survey (SDSS) spectra of quasars. Taking into account the selection effects that result from dust extinction, including the reduction in the signal-to-noise ratio of an absorber appearing in a reddened quasar spectrum, we find a stronger dependence of E(B-V) on absorber rest equivalent width (EW) than in other published work. The dependence of the median reddening on EW can be reproduced by a power-law model: E(B-V)=.8+/-3*10-4 * EW^(3.48+/-0.3) for 1.0A<EW<5.0A. Observed Mg II samples, derived from flux-limited quasar surveys, are shown to suffer from significant incompleteness at the level of 24+/-4 per cent for absorbers with EW>1A and 34+/-2 per cent for absorbers with EW>2A. Direct determination of the shape of the near-ultraviolet extinction curves for absorbers as a function of E(B-V) show evidence for systematic changes in the form of the extinction curves. At low E(B-V) (>0.05), the extinction curve is well represented by a Small Magellanic Cloud-like extinction curve. For intermediate E(B-V)s (<0.2), approximately a third of MgII absorbers show evidence for a 2175A feature similar to that of the Large Magellanic Cloud. For the small number of high E(B-V) (>0.3) absorbers, the majority of which exhibit strong CaII 3935,3970 absorption, there is evidence for a 2175A feature as strong as that found in the Milky Way. Application of the new results on the dust content of strong Mg II absorbers shows that dusty absorbers can account for a significant proportion, up to a factor of two, of the observed overdensity of absorbers seen towards Gamma-Ray Burst (GRB) sightlines, compared to sightlines towards quasars in flux-limited samples. (Abridged)Comment: 21 pages, 20 figures, 2 tables, accepted for publication in MNRA

Bounds for Lepton Flavor Violation and the Pseudoscalar Higgs in the General Two Higgs Doublet Model using g−2g-2 muon factor

Current experimental data from the $g-2$ muon factor, seems to show the necessity of physics beyond the Standard Model (SM), since the difference between SM and experimental predictions is 2.6$\sigma$. In the framework of the General Two Higgs Doublet Model (2HDM), we calculate the muon anomalous magnetic moment to get lower and upper bounds for the Flavour Changing (FC) Yukawa couplings in the leptonic sector. We also obtain lower bounds for the mass of the pseudoscalar Higgs ($m_{A^0}$) as a function of the parameters of the model.Comment: 12 pages, RevTex4, 5 figures. Improved presentation, updated experimental data, amplified analysis, new figures added. Subbmited to Phys. Rev.