119200038
Search for gauge extensions of the MSSM at the LHC
The extensions of the minimal supersymmetric model (MSSM), driving mainly from the need to solve the $\ensuremath{\mu}$ problem, involve novel matter species and gauge groups. These extended MSSM models can be searched for at the LHC via the effects of the gauge and Higgs bosons or their fermionic partners. Traditionally, the focus has been on the study of the extra forces induced by the new gauge and Higgs bosons present in such models. An alternative way of studying such effects is through the superpartners of matter species and the gauge forces. We thus consider a $U(1{)}^{\ensuremath{'}}$ gauge extension of the MSSM, and perform an extensive study of the signatures of the model through the production and decays of the scalar quarks and gluino, which are expected to be produced copiously at the LHC. After a detailed study of the distinctive features of such models with regard to the signatures at the LHC, we carry out a detailed Monte Carlo analysis of the signals from the process $pp\ensuremath{\rightarrow}n\text{ }\mathrm{\text{leptons}}+m\text{ }\mathrm{\text{jets}}+{\mathrm{E\ensuremath{\llap{\not\;}}}}_{T}$, and compare the resulting distributions with those predicted by the MSSM. Our results show that the searches for the extra gauge interactions in the supersymmetric framework can proceed not only through the forces mediated by the gauge and Higgs bosons but also through the superpartner forces mediated by the gauge and Higgs fermions. Analysis of the events induced by the squark/gluino decays presented here is complementary to the direct ${Z}^{\ensuremath{'}}$ searches at the LHC.
121188586
Heavy quark physics at HERA
Abstract A brief overview of the anticipated heavy quark physics at HERA is given. The topics discussed include heavy quark photo- and leptoproduction cross sections at HERA calculated in the context of perturbative QCD, various mechanisms of J / ϕ -leptoproduction and their rates, determination of the gluon density of the proton using open and bound charmed hadrons, and rare D 0 -meson decays. Some selected aspects of B -Physics at HERA are also discussed.
10853970
Rare B decays in the standard model
Abstract We discuss the electromagnetic-penguin-dominated radiative B decays B → X s + γ , B ±(0) → K ∗±(0) + γ , and B s → φ + γ in the context of the Standard Model (SM) and their Cabibbo-Kobayashi-Maskawa (CKM)-suppressed counterparts, B → X d + γ , B ± → ϱ ± + γ , B 0 → ( ϱ 0 , ω ) + γ , and B s → K ∗0 + γ , using QCD sum rules for the exclusive decays. The importance of these decays in determining the parameters of the CKM matrix [1] is emphasized. The semileptonic decays B → X s l + l − are also discussed in the context of the SM and their role in determining the Wilson coefficients of the effective theory is stressed. Comparison with the existing measurements are made and SM-based predictions for a large number of rare B decays are presented.
13281897
Majorana neutrinos and same-sign dilepton production at LHC and in rare meson decays
Abstract. We discuss same-sign dilepton production mediated by Majorana neutrinos in high-energy proton–proton collisions $pp\rightarrow \ell^+ \ell^{\prime +}X$ for $\ell, \ell^\prime = e, \mu, \tau$ at the LHC energy $ s^{1/2} =14$ TeV, and in the rare decays of the $K, D, D_s$, and B mesons of the type $M^+\rightarrow M^{\prime -}\ell ^+\ell ^{\prime+}$. For the pp reaction, assuming one heavy Majorana neutrino of mass $m_N$, we present discovery limits in the $\left(m_N,\left|U_{\ell N}U_{\ell^\prime N}\right|\right)$ plane where $U_{\ell N}$ are the mixing parameters. Taking into account the present limits from low-energy experiments, we show that at LHC one has sensitivity to heavy Majorana neutrinos up to a mass $m_N\leq 2--5$ TeV in the dilepton channels $\mu\mu, \tau\tau$, and $\mu\tau$, but the dilepton states $e\ell$ will not be detectable due to the already existing constraints from neutrinoless double beta decay. We work out a large number of rare meson decays, both for the light and heavy Majorana neutrino scenarios, and argue that the present experimental bounds on the branching ratios are too weak to set reasonable limits on the effective Majorana masses.
117235251
B Decays in the Standard Model - Status and Perspectives
These lectures review some of the progress made in the quantitative understanding of B decays. The emphasis here is on applications of QCD using perturbative and non-perturbative techniques. In some cases, however, phenomenological models must at present be invoked to make meaningful comparison with data. The resulting picture is consistent with the standard model (SM) and this agreement is quantified in terms of the branching ratios, mixing probabilities, and lifetimes which measure the charge current and effective flavour changing neutral current transitions involving B hadrons. This, in turn, enables a determination of five of the nine elements of the quark mixing matrix. We discuss several proposals on improving the precision on the parameters of this matrix in forthcoming experiments. Issues intimately related to the quark mixing matrix such as the profile of the unitarity triangle and CP-violating asymmetries in B decays are discussed. In particular, we emphasize the role of rare B decays and B^0 - $\overline{B^0}$ mixings in testing the SM quantitatively and in searching for physics beyond the SM.
117634637
The LHC signatures of the extended gauge structures in supersymmetry
118780957
Discreteness of space from the generalized uncertainty principle
Various approaches to Quantum Gravity (such as String Theory and Doubly Special Relativity), as well as black hole physics predict a minimum measurable length, or a maximum observable momentum, and related modifications of the Heisenberg Uncertainty Principle to a so-called Generalized Uncertainty Principle (GUP). We propose a GUP consistent with String Theory, Doubly Special Relativity and black hole physics, and show that this modifies all quantum mechanical Hamiltonians. When applied to an elementary particle, it implies that the space which confines it must be quantized. This suggests that space itself is discrete, and that all measurable lengths are quantized in units of a fundamental length (which can be the Planck length). On the one hand, this signals the breakdown of the spacetime continuum picture near that scale, and on the other hand, it can predict an upper bound on the quantum gravity parameter in the GUP, from current observations. Furthermore, such fundamental discreteness of space may have observable consequences at length scales much larger than the Planck scale.
119191368
Minimal length in quantum gravity, equivalence principle and holographic entropy bound
A possible discrepancy has been found between the results of a neutron interferometry experiment and quantum mechanics. This experiment suggests that the weak equivalence principle is violated at small length scales, which quantum mechanics cannot explain. In this paper, we investigated whether the generalized uncertainty principle (GUP), proposed by some approaches to quantum gravity such as string theory and doubly special relativity theories, can explain the violation of the weak equivalence principle at small length scales. We also investigated the consequences of the GUP on the Liouville theorem in statistical mechanics. We have found a new form of invariant phase space in the presence of GUP. This result should modify the density states and affect the calculation of the entropy bound of local quantum field theory, the cosmological constant, black body radiation, etc. Furthermore, such modification may have observable consequences at length scales much larger than the Planck scale. This modification leads to a -type correction to the bound of the maximal entropy of a bosonic field which would definitely shed some light on the holographic theory.
46115571
A proposal for testing quantum gravity in the lab
Attempts to formulate a quantum theory of gravitation are collectively known as {\it quantum gravity}. Various approaches to quantum gravity such as string theory and loop quantum gravity, as well as black hole physics and doubly special relativity theories predict a minimum measurable length, or a maximum observable momentum, and related modifications of the Heisenberg Uncertainty Principle to a so-called generalized uncertainty principle (GUP). We have proposed a GUP consistent with string theory, black hole physics and doubly special relativity theories and have showed that this modifies all quantum mechanical Hamiltonians. When applied to an elementary particle, it suggests that the space that confines it must be quantized, and in fact that all measurable lengths are quantized in units of a fundamental length (which can be the Planck length). On the one hand, this may signal the breakdown of the spacetime continuum picture near that scale, and on the other hand, it can predict an upper bound on the quantum gravity parameter in the GUP, from current observations. Furthermore, such fundamental discreteness of space may have observable consequences at length scales much larger than the Planck scale. Because this influences all the quantum Hamiltonians in an universal way, it predicts quantum gravity corrections to various quantum phenomena. Therefore, in the present work we compute these corrections to the Lamb shift, simple harmonic oscillator, Landau levels, and the tunneling current in a scanning tunneling microscope.