Symmetry breaking and electroweak physics at Photon Linear Colliders

The physics potential of a high-energy photon collider is reviewed. The emphasis is put on aspects related to the symmetry breaking sector, including Higgs searches and production of longitudinal vector bosons.Comment: LATEX, 12 pages, 3 fig, macros included, no changes in pape

Dark matter and the LHC

Cosmological and astrophysical measurements indicate that the universe contains a large amount of dark matter. A number of weak scale dark matter candidates have been proposed in extensions of the standard model. The potential to discover the dark matter particle and determine its properties at the upcoming LHC is summarized.Comment: 6 pages, 4 figures, Talk at Dark matter and dark energy, GGI, Florence, Italy, March 200

Assisted freeze-out

We explore a class of dark matter models with two dark matter candidates, only one interacts with the standard model sector. One of the dark matter is thermalized with the assistance of the other stable particle. While both stable particles contribute to the total relic density only one can elastically scatter with nuclei, thus effectively reducing the direct detection rate.Comment: 16 pages, 13 figures, minor corrections, the final version published in JCA

Invisible Decays of the Supersymmetric Higgs and Dark Matter

We discuss effects of the light sparticles on decays of the lightest Higgs in a supersymmetric model with nonuniversal gaugino masses at the high scale, focusing on the `invisible' decays into neutralinos. These can impact significanlty the discovery possibilities of the lightest Higgs at the LHC. We show that due to these decays, there exist regions of the $M_2-\mu$ space where the B.R. $(h \to \gamma \gamma)$ becomes dangerously low even after imposing the LEP constraints on the sparticle masses, implying a possible preclusion of its discovery in the $\gamma \gamma$ channel. We find that there exist regions in the parameter space with acceptable relic density and where the ratio ${B.R. (h \to \gamma \gamma)_{SUSY} \over B.R. (h \to \gamma \gamma)_{SM}}$ falls below 0.6, implying loss of signal in the $\gamma \gamma$ channel. These regions correspond to $\tilde \chi_1^+, \tilde \chi_2^0$ masses which should be accessible already at the Tevatron. Further we find that considerations of relic density put lower limit on the U(1) gaugino mass parameter $M_1$ independently of $\mu, \tan \beta$ and $m_0$.Comment: 17 pages, 11 figures, Talk presented at Appi2002, Accelerator and Particle Physics Institute, Appi, Iwate, Japan, February 13--16 200

Impact of semi-annihilations on dark matter phenomenology - an example of Z_N symmetric scalar dark matter

We study the impact of semi-annihilations x_i x_j x_k X, where x_i is any dark matter and X is any standard model particle, on dark matter phenomenology. We formulate minimal scalar dark matter models with an extra doublet and a complex singlet that predict non-trivial dark matter phenomenology with semi-annihilation processes for different discrete Abelian symmetries Z_N, N>2. We implement two such example models with Z_3 and Z_4 symmetry in micrOMEGAs and work out their phenomenology. We show that both semi-annihilations and annihilations involving only particles from two different dark matter sectors significantly modify the dark matter relic abundance in this type of models. We also study the possibility of dark matter direct detection in XENON100 in those models.Comment: 17 pages, 4 figure

Status and prospects of the nMSSM after LHC Run-1

The new minimal supersymmetric standard model (nMSSM), a variant of the general next to minimal supersymmetric standard model (NMSSM) without $Z_3$ symmetry, features a naturally light singlino with a mass below 75 GeV. In light of the new constraints from LHC Run-1 on the Higgs couplings, sparticles searches and flavour observables, we define the parameter space of the model which is compatible with both collider and dark matter (DM) properties. Among the regions compatible with these constraints, implemented through NMSSMTools, SModelS and MadAnalysis 5, only one with a singlino lightest supersymmetric particle (LSP) with a mass around 5 GeV can explain all the DM abundance of the universe, while heavier mixed singlinos can only form one of the DM components. Typical collider signatures for each region of the parameter space are investigated. In particular, the decay of the 125 GeV Higgs into light scalars and/or pseudoscalars and the decay of the heavy Higgs into charginos and neutralinos, provide distinctive signatures of the model. Moreover, the sfermion decays usually proceed through heavier neutralinos rather than directly into the LSP, as the couplings to the singlino are suppressed. We also show that direct detection searches are complementary to collider ones, and that a future ton-scale detector could completely probe the region of parameter space with a LSP mass around 65 GeV.Comment: 33 pages, 9 figures. Version accepted for publication in JHE

Uncertainties in the Prediction of the Relic Density of Supersymmetric Dark Matter

We investigate how well the relic density of dark matter can be predicted in mSUGRA. We determine the parameters to which the relic density is most sensitive and quantify the collider accuracy needed to match the accuracy of WMAP and PLANCK.Comment: 4 pages, 1 figure, presented at LCWS, Paris, April 200

Higgs Phenomenology of Minimal Universal Extra Dimensions

The minimal model of Universal Extra Dimensions (MUED) is briefly reviewed. We explain how the cross-sections for Higgs production via gluon fusion and decay into two photons are modified, relative the the Standard Model (SM) values, by KK particles running in loops, leading to an enhancement of the gg to h to two photons and gg to h to W+W- cross-sections. ATLAS and CMS searches for the SM Higgs in these channels are reinterpreted in the context of MUED and used to place new limits on the MUED parameter space. Only a small region of between 1 and 3 GeV around mh = 125 GeV for 500 GeV < 1/R < 1600 GeV remains open at the 95 % confidence level.Comment: Presented at the 2011 Hadron Collider Physics symposium (HCP-2011), Paris, France, November 14-18 2011, 3 pages, 4 figure

Extracting constraints from direct detection searches of supersymmetric dark matter in the light of null results from the LHC in the squark sector

The comparison of the results of direct detection of Dark Matter, obtained with various target nuclei, requires model-dependent, or even arbitrary, assumptions. Indeed, to draw conclusions either the spin-dependent (SD) or the spin-independent (SI) interaction has to be neglected. In the light of the null results from supersymmetry searches at the LHC, the squark sector is pushed to high masses. We show that for a squark sector at the TeV scale, the framework used to extract contraints from direct detection searches can be redefined as the number of free parameters is reduced. Moreover, the correlation observed between SI and SD proton cross sections constitutes a key issue for the development of the next generation of Dark Matter detectors.Comment: Figure 3 has been updated. Conclusions unchange