Search results for "Model theory"
showing 10 items of 681 documents
Transverse-momentum dependence of theJ/ψnuclear modification ind+Au collisions atsNN=200GeV
2013
We present measured J/psi production rates in d + Au collisions at root s(NN) = 200 GeV over broad ranges of transverse momentum (p(T) = 0-14 GeV/c) and rapidity (-2.2 1) for p(T) > 2 GeV/c. The observed enhancement at negative rapidity has implications for the interpretation of the observed modification in heavy-ion collisions at high p(T). DOI: 10.1103/PhysRevC.87.034904
Supersymmetric mass spectra and the seesaw type-I scale
2012
We calculate supersymmetric mass spectra with cMSSM boundary conditions and a type-I seesaw mechanism added to explain current neutrino data. Using published, estimated errors on SUSY mass observables for a combined LHC+ILC analysis, we perform a theoretical $\chi^2$ analysis to identify parameter regions where pure cMSSM and cMSSM plus seesaw type-I might be distinguishable with LHC+ILC data. The most important observables are determined to be the (left) smuon and selectron masses and the splitting between them, respectively. Splitting in the (left) smuon and selectrons is tiny in most of cMSSM parameter space, but can be quite sizeable for large values of the seesaw scale, $m_{SS}$. Thus,…
Supersymmetric type-III seesaw mechanism: Lepton flavor violating decays and dark matter
2011
We study a supersymmetric version of the seesaw mechanism type III. The model consists of the minimal supersymmetric extension of the standard model particle content plus three copies of $\mathbf{24}$ superfields. The fermionic part of the $SU(2)$ triplet contained in the $\mathbf{24}$ is responsible for the type-III seesaw, which is used to explain the observed neutrino masses and mixings. Complete copies of $\mathbf{24}$ are introduced to maintain gauge coupling unification. These additional states change the beta functions of the gauge couplings above the seesaw scale. Using minimal Supergravity boundary conditions, we calculate the resulting supersymmetric mass spectra at the electrowea…
LHCb pentaquark as aD¯*Σc−D¯*Σc*molecular state
2015
We perform a theoretical analysis of the ${\mathrm{\ensuremath{\Lambda}}}_{b}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}^{\ensuremath{-}}p$ reaction from where a recent LHCb experiment extracts a $\mathrm{\ensuremath{\Lambda}}(1405)$ contribution in the ${K}^{\ensuremath{-}}p$ spectrum close to threshold and two baryon states of hidden charm in the $J/\ensuremath{\psi}p$ spectrum. We recall that baryon states of this type have been theoretically predicted matching the mass, width and ${J}^{P}$ of the experiment; concretely some states built up from the $J/\ensuremath{\psi}N$, ${\overline{D}}^{*}{\mathrm{\ensuremath{\Lambda}}}_{c}$, ${\overline{D}}^{*}{\mathrm{\ensuremath{\Sigma}}}_{c}$, …
Large-$N_c$ naturalness in coupled-channel meson-meson scattering
2014
The analysis of hadronic interactions with effective field theory techniques is complicated by the appearance of a large number of low-energy constants, which are usually fitted to data. On the other hand, the large-$N_c$ limit imposes natural short-distance constraints on these low-energy constants, providing a parameter reduction. A Bayesian interpretation of the expected $1/N_c$ accuracy allows for an easy and efficient implementation of these constraints, using an augmented $\chi^2$. We apply this approach to the analysis of meson-meson scattering, in conjunction with chiral perturbation theory to one loop and coupled-channel unitarity, and show that it helps to largely reduce the many …
Flavour-violating charged lepton decays in seesaw-type models
1994
Analytic expressions of lepton-flavour- and lepton-number-violating decays of charged leptons are derived in the context of general $SU(2)_L\otimes U(1)_Y$ seesaw scenarios that are motivated by grand unified theories (GUT's) or superstring models, in which left-handed and/or right-handed neutral singlets are present. Possible constraints imposed by cosmology and low-energy data are briefly discussed. The violation of the decoupling theorem in flavour-dependent graphs due to the presence of heavy neutral leptons of Dirac or Majorana nature is emphasized. Numerical estimates reveal that the decays $\tau^-\to e^-e^-e^+$ or $\tau^-\to e^-\mu^-\mu^+$ can be as large as $\sim 10^{-6}$, which may…
A realistic model of neutrino masses with a large neutrinoless double beta decay rate
2011
The minimal Standard Model extension with the Weinberg operator does accommodate the observed neutrino masses and mixing, but predicts a neutrinoless double beta ($0\nu\beta\beta$) decay rate proportional to the effective electron neutrino mass, which can be then arbitrarily small within present experimental limits. However, in general $0\nu\beta\beta$ decay can have an independent origin and be near its present experimental bound; whereas neutrino masses are generated radiatively, contributing negligibly to $0\nu\beta\beta$ decay. We provide a realization of this scenario in a simple, well defined and testable model, with potential LHC effects and calculable neutrino masses, whose two-loop…
Inverse tribimaximal type-III seesaw mechanism and lepton flavor violation
2009
We present a type-III version of inverse seesaw or, equivalently an inverse version of type-III seesaw. Naturally small neutrino masses arise at low-scale from the exchange of neutral fermions transforming as hyperchargeless SU(2) triplets. In order to implement tri-bimaximal lepton mixing we supplement the minimal SU(3)xSU(2)xU(1) gauge symmetry with an A4-based flavor symmetry. Our scenario induces lepton flavour violating (LFV) three body decays that can proceed at the tree level, while radiative li to lj gamma decays and mu-e conversion in nuclei are also expected to be sizeable. LFV decays are related by the underlying flavor symmetry and the new fermions are also expected to be access…
Photo-transmutation of leptons
2001
By photo-transmutation of leptons we mean photon-lepton reactions of the following type: $\gamma l_\alpha \longrightarrow \gamma l_\beta$ with $l_\alpha \neq l_\beta$, occurring as a consequence of the lepton mass matrix changing its orientation (rotating) under changing scales. In this paper, we first discuss these reactions in general terms, then proceed to the calculation of their cross sections in two specific schemes, one within the framework of the conventional Standard Model, the other being the so-called Dualized Standard Model we ourselves advocate. Although the cross section obtained is generally small the calculation reveals certain special circumstances where these reactions may…
Observation of monojet events and tentative interpretation
1994
Abstract A data sample corresponding to almost two million hadronic Z decays collected by the ALEPH detector at LEP has been searched for monojet events. Three events were found, in agreement with the expectation from the process e + e − → γ * v v ¯ , with γ * → f f ¯ . Two events are hadronic, the third one being an e + e − pair. All monojet masses are in excess of 3 GeV/ c 2 , and two of the event have large transverse momenta: 18.5 and 20.3 GeV/ c . These kinematic characteristics are quite unlikely in the process e + e − → γ * v v ¯ . The probability of their occurence increases substantially when processes involving further Z or W exchanges are taken into account, but still remains at …