LHC signals of T-odd heavy quarks in the Littlest Higgs model

Recently proposed Little Higgs models present a viable solution to the naturalness problem of the Standard Model. An additional discrete symmetry, called T-parity, has been included in the simplest Little Higgs models to evade the constraints arising from electroweak precision data. The Littlest Higgs model with T-parity (LHT) not only predicts a set of new fermions in addition to the heavy gauge bosons of the original Little Higgs model, but also provides a new candidate for dark matter. In this paper, we study two particularly interesting signatures of T-odd fermion pair production at the LHC, namely, (a) jj + l^+ l^- + missing E_T and (b) jj + b \bar b + l^\pm + missing E_T. Using a parton level Monte Carlo event generator, we evaluate both the signal as well as the standard model background profile for a selected set of model parameters thereby developing a good discriminator. Finally, we scan the parameter space and delineate the possible discovery region in the same

Unparticle physics in top pair signals at the LHC and ILC

We study the effects of unparticle physics in the pair productions of top quarks at the LHC and ILC. By considering vector, tensor and scalar unparticle operators, as appropriate, we compute the total cross sections for pair production processes depending on scale dimension d_{\U}. We find that the existence of unparticles would lead to measurable enhancements on the SM predictions at the LHC. In the case of ILC this may become two orders of magnitude larger than that of SM, for smaller values of d_\U, a very striking signal for unparticles.Comment: 19 pages, 9 figures, analysis for ILC has been adde

Anomaly mediated supersymmetry breaking and its test in linear colliders

Signatures of anomaly mediated supersymmetry breaking in linear colliders are briefly reviewed after presenting an outline of the theoretical framework. A unique and distinct feature of a large class of models of this type is a winolike chargino which is very closely degenerate in mass with the lightest neutralino. The very slow decay of this chargino results in a heavily ionizing charged track and one soft charged pion with a characteristic momentum distribution, leading to unique signals in linear colliders which are essentially free of background. The determination of chargino and slepton masses from such events is a distinctly interesting possibility.Comment: 15 pages, LaTex, 4 PS figures, ws-mpla.cls file included. One reference added. To appear as a Brief Review in Modern Physics Letters

Single top quark production as a probe of R-parity-violating SUSY at pp and p\bar p colliders

We investigate the ability of single top quark production via qq'-> squark->tb and q \bar q'->slepton->t\bar b at the LHC and Tevatron to probe the strength of R-parity violating couplings in the minimal supersymmetric model. We found that given the existing bounds on R-parity violating couplings, single top quark production may be greatly enhanced over that predicted by the standard model, and that both colliders can either discover R-parity violating SUSY or set strong constraints on the relevant R-parity violating couplings. We further found that the LHC is much more powerful than the Tevatron in probing the squark couplings, but the two colliders have comparable sensitivity for the slepton couplings.Comment: 15 pages, 4 figure

Supersymmetric interpretation of high--Q2Q^2 HERA events and other related issues

In the framework of the minimal supersymmetric standard model (MSSM) with $R-$parity violation, the high--$Q^2$ HERA events can be interpreted as the $s-$channel production of a single stop of $M_{\tilde{t}_1} \approx 200$ GeV, whose dominant decay modes are assumed to be the $R-$parity violating $e^+ + d$ and the $R-$parity conserving $\chi^+ + b$. Assuming only one coupling $\bar{\lambda_{131}^{'}}$ is nonzero of order $\sim 0.04-0.12$, we find that (i) the high$-Q^2$ HERA events can be understood as an $s-$channel stop production with a subsequent decay into $e^+ + (single ~jet)$, and (ii) the ALEPH 4-jet events can be understood in the scenario suggested by Carena et al.. We briefly discuss other physics signals of this scenario at other places such as HERA, LEP200 and Tevatron. The best test for our scenario is to observe the stop decay into $\chi^+ + b$ followed by $\chi^+ \to \tilde{e}^+ + \nu_e$ and $\tilde{e}^+ \to q + \bar{q}^{'}$ via the $R-$parity violating coupling.Comment: version published in Phys. Rev. D. 57 (1998) 489-49

Unparticle Physics in Single Top Signals

We study the single production of top quarks in $e^+e^-, ep$ and $pp$ collisions in the context of unparticle physics through the Flavor Violating (FV) unparticle vertices and compute the total cross sections for single top production as functions of scale dimension d_{\U}. We find that among all, LHC is the most promising facility to probe the unparticle physics via single top quark production processes.Comment: 14 pages, 10 figure

Constraining Bosonic Supersymmetry from Higgs results and 8 TeV ATLAS multi-jets plus missing energy data

The collider phenomenology of models with Universal Extra Dimensions (UED) is surprisingly similar to that of supersymmetric (SUSY) scenarios. For each level-1 bosonic (fermionic) Kaluza-Klein (KK) state, there is a fermionic (bosonic) analog in SUSY and thus UED scenarios are often known as bosonic supersymmetry. The minimal version of UED (mUED) gives rise to a quasi-degenerate particle spectrum at each KK-level and thus, can not explain the enhanced Higgs to diphoton decay rate hinted by the ATLAS collaboration of the Large Hadron Collider (LHC) experiment. However, in the non-minimal version of the UED (nmUED) model, the enhanced Higgs to diphoton decay rate can be easily explained via the suitable choice of boundary localized kinetic (BLK) terms for higher dimensional fermions and gauge bosons. BLK terms remove the degeneracy in the KK mass spectrum and thus, pair production of level-1 quarks and gluons at the LHC gives rise to hard jets, leptons and large missing energy in the final state. These final states are studied in details by the ATLAS and CMS collaborations in the context of SUSY scenarios. We find that the absence of any significant deviation of the data from the Standard Model (SM) prediction puts a lower bound of about 2.1 TeV on equal mass excited quarks and gluons.Comment: 19 page

Constraints on Astro-unparticle Physics from SN 1987A

SN 1987A observations have been used to place constraints on the interactions between standard model particles and unparticles. In this study we calculate the energy loss from the supernovae core through scalar, pseudo scalar, vector, pseudo vector unparticle emission from nuclear bremsstrahlung for degenerate nuclear matter interacting through one pion exchange. In order to examine the constraints on $d_{\cal U}=1$ we considered the emission of scalar, pseudo scalar, vector, pseudo vector and tensor through the pair annihilation process $e^+e^-\to {\cal U} \gamma$. In addition we have re-examined other pair annihilation processes. The most stringent bounds on the dimensionless coupling constants for $d_{\cal U} =1$ and $\Lambda_{\cal U}= m_Z$ are obtained from nuclear bremsstrahlung process for the pseudo scalar and pseudo-vector couplings $\bigl|\lambda^{\cal P}_{0,1}\bigr|\leq 4\times 10^{-11}$ and for tensor interaction, the best limit on dimensionless coupling is obtained from $e^+ e^-\to {\cal U} \gamma$ and we get $\bigl|\lambda^{\cal T}\bigr| \leq 6\times 10^{-6}$.Comment: 12 pages, 2 postscript figure