Search

We build rigorously the attractive five-dimensional model where bulk fermions propagate along the ${\mathcal{S}}^{1}/{\mathbb{Z}}_{2}$ orbifold and interact with a Higgs boson localized at a fixed point of the extra dimension. The analytical calculation of the fermion mass spectrum and effective Yukawa couplings is shown to require the introduction of either essential boundary conditions (EBC) imposed by the model definition or certain bilinear brane terms (BBT) in the action, instead of the usual brane-Higgs regularizations. The obtained fermion profiles along the extra dimension turn out to undergo some discontinuities, in particular at the Higgs brane, which can be mathematically consistent if the action is well written with improper integrals. We also show that the ${\mathbb{Z}}_{2}$ parity transformations in the bulk do not affect the fermion chiralities, masses and couplings, in contrast with the EBC and the BBT, but when extended to the fixed points, they can generate the chiral nature of the theory and even select the Standard Model chirality setup while fixing as well the fermion masses and couplings. Thanks to the strict analysis developed, the duality with the interval model is scrutinized.

The studies of the Higgs boson couplings based on the recent and upcoming LHC data open up a new window on physics beyond the Standard Model. In this paper, we propose a statistical guide to the consistent treatment of the theoretical uncertainties entering the Higgs rate fits. Both the Bayesian and frequentist approaches are systematically analysed in a unified formalism. We present analytical expressions for the marginal likelihoods, useful to implement simultaneously the experimental and theoretical uncertainties. We review the various origins of the theoretical errors (QCD, EFT, PDF, production mode contamination...). All these individual uncertainties are thoroughly combined with the help of moment-based considerations. The theoretical correlations among Higgs detection channels appear to affect the location and size of the best-fit regions in the space of Higgs couplings. We discuss the recurrent question of the shape of the prior distributions for the individual theoretical errors and find that a nearly Gaussian prior arises from the error combinations. We also develop the bias approach, which is an alternative to marginalisation providing more conservative results. The statistical framework to apply the bias principle is introduced and two realisations of the bias are proposed. Finally, depending on the statistical treatment, the Standard Model prediction for the Higgs signal strengths is found to lie within either the $68\%$ or $95\%$ confidence level region obtained from the latest analyses of the $7$ and $8$ TeV LHC datasets., 62 pages, 10 figures

The class of higher-dimensional scenarios, based on a brane-localised Higgs boson coupled to bulk fermions, can address both the flavour puzzle and gauge hierarchy problem. A key question arises due to the possibility of fermion profile discontinuities at the Higgs boundary: how to calculate rigorously the fermion mass spectrum and effective four-dimensional (4D) Yukawa couplings? We show that the proper treatment, leading to physically consistent solutions, does not rely on any Higgs peak regularisation but requires the presence of certain Bilinear Brane Terms (BBT). In particular, no profile jump should appear and the Higgs regularisations turn out to suffer from mathematical discrepancies reflected in two non-commutativities of calculation steps debated in the literature. The introduction of BBT can by replaced by vanishing conditions for probability currents at the considered flat interval boundaries. Both contribute to the definition of the field geometrical configuration of the model, even in the free case. The BBT could allow to elaborate an ultra-violet origin of the chiral nature of the Standard Model and of its chirality distribution among quarks/leptons. The current conditions are implemented via essential boundary conditions to be contrasted with the natural boundary conditions derived from the action variation. All these theoretical conclusions are confirmed in particular by the converging exact results of the 4D versus 5D approaches. The analysis is completed by a description of the appropriate energy cut-off procedure. The new calculation methods presented, implying the independence of excited fermion masses and 4D Yukawa couplings on the 'wrong-chirality' Yukawa terms, have impacts on phenomenological results like the relaxing of previously obtained strong bounds on Kaluza-Klein masses induced by flavour changing reactions generated through exchanges of the Higgs field., Comment: 50 pages, 1 figure, 1 table, Latex file

The radion scalar field might be the lightest new particle predicted by extra-dimensional extensions of the Standard Model. It could thus lead to the first signatures of new physics at the LHC collider. We perform a complete study of the radion production in association with the Z gauge boson in the custodially protected warped model with a brane-localised Higgs boson addressing the gauge hierarchy problem. Radion-Higgs mixing effects are present. Such a radion production receives possibly resonant contributions from the Kaluza-Klein excitations of the Z boson as well as the extra neutral gauge boson (Z'). All the exchange and mixing effects induced by those heavy bosons are taken into account in the radion coupling and rate calculations. The investigation of the considered radion production at LHC allows to be sensitive to some parts of the parameter space but only the ILC program at high luminosity would cover most of the theoretically allowed parameter space via the studied reaction. Complementary tests of the same theoretical parameters can be realised through the high accuracy measurements of the Higgs couplings at ILC. The generic sensitivity limits on the rates discussed for the LHC and ILC potential reach can be applied to the searches for other (light) exotic scalar bosons., Comment: 28 pages, 10 figures

The imperfect knowledge of the Higgs boson decay rates and cross sections at the LHC constitutes a critical systematic uncertainty in the study of the Higgs boson properties. We show that the full covariance matrix between the Higgs rates can be determined from the most elementary sources of uncertainty by a direct application of probability theory. We evaluate the error magnitudes and full correlation matrix on the set of Higgs cross sections and branching ratios at $\sqrt{s}=7$, $8$, $13$ and $14$ TeV, which are provided in ancillary files. The impact of this correlation matrix on the global fits is illustrated with the latest $7$+$8$ TeV Higgs dataset., 25 pages, 1 figure. Complete covariance matrix is available in C, Fortran, Mathematica, PDF, TeX and text formats in ancillary files

We consider the Randall-Sundrum extra dimensional model with fields propagating in the bulk based on an extended electroweak gauge symmetry with specific fermion charges and localizations that allow to explain the LEP anomaly of the forward--backward asymmetry for $b$--quarks, $A_{FB}^b$. We study the manifestations of the strongly--interacting and electroweak gauge boson Kaluza--Klein excitations $\vkk$ at the LHC, with masses of the order of a few TeV, which dominantly decays into top and bottom quark pairs. We first analyze the two--body tree--level production processes $pp \to t\bar t$ and $b\bar b$ in which the Kaluza--Klein (KK) excitations of gauge bosons are exchanged. We find that the additional channels can lead to a significant excess of events with respect to the Standard Model prediction; characteristic top quark polarization and angular asymmetries are quantitatively studied and turn out to probe the chiral structure of couplings to excited states. We then analyze higher order production processes for the gauge boson excitations which have too weak or no couplings to light quarks and, in particular, the loop induced process $gg \to \vkk \to t\bar t$ and $b\bar b$ in which the anomalous $gg \vkk $ four--dimensional vertex has to be regulated. The RS effects in this process, as well as in the four--body reactions $pp \to t\bar t b\bar b$, $t\bar t t\bar t$, $b\bar b b\bar b$ and in the related three--body reactions $gb \to b t \bar t$, $b b\bar b$, in which the $\vkk$ excitations are mainly radiated off the eavy quarks, are shown to be potentially difficult to test at LHC, due to small hase space and low parton density for $\mkk \gsim 3$ TeV., 31 pages, 9 figures, usages axodraw.sty (included)

It is notorious that, contrary to all other precision electroweak data, the forward-backward asymmetry for b quarks $A_{FB}^b$ measured in Z decays at LEP1 is nearly three standard deviations away from the predicted value in the Standard Model; significant deviations also occur in measurements of the asymmetry off the Z pole. We show that these discrepancies can be resolved in a variant of the Randall-Sundrum extra-dimensional model in which the gauge structure is extended to $SU(2)_L \times SU(2)_R \times U(1)_X$ to allow for relatively light Kaluza-Klein excitations of the gauge bosons. In this scenario, the fermions are localized differently along the extra dimension, in order to generate the fermion mass hierarchies, so that the electroweak interactions for the heavy third generation fermions are naturally different from the light fermion ones. We show that the mixing between the Z boson with the Kaluza-Klein excitations allows to explain the $A_{FB}^b$ anomaly without affecting (and even improving) the agreement of the other precision observables, including the $Z \to bb$ partial decay width, with experimental data. Some implications of this scenario for the ILC are summarized., Comment: 23 pages, 5 figures

Vector-like quarks (VLQs) that are partners of the heavy top and bottom quarks are predicted in many extensions of the Standard Model (SM). We explore the possibility that these states could explain not only the longstanding anomaly in the forward-backward asymmetry in $b$-quark production at LEP, $A_{\rm FB}^b $, but also the more recent $\sim 2\sigma$ deviation of the cross section for the associated Higgs production with top quark pairs at the LHC, $\sigma(pp\to t\bar t H)$. Introducing three illustrative models for VLQs with different representations under the SM gauge group, we show that the two anomalies can be resolved while satisfying all other theoretical and experimental constraints. In this case, the three different models predict VLQ states in the $1-2$ TeV mass range that can be soon probed at the LHC. In a second step, we discuss the sensitivity on the VLQ masses and couplings that could be obtained by means of a percent level accuracy in the measurement of ratios of partial Higgs decay widths, in particular $\Gamma(H \! \to\! \gamma\gamma)/\Gamma(H \! \to\! ZZ^*)$ and $\Gamma(H \! \to \! b\bar b)/\Gamma(H \! \to \! WW^*)$. We show that top and bottom VL partners with masses up to $\sim 5$ TeV and exotic VLQs with masses in the $10$ TeV range can be probed at the high-luminosity LHC., Comment: 27 pages, 6 figures; v2: added references

Theoretical and phenomenological implications of R-parity violation in supersymmetric theories are discussed in the context of particle physics and cosmology. Fundamental aspects include the relation with continuous and discrete symmetries and the various allowed patterns of R-parity breaking. Recent developments on the generation of neutrino masses and mixings within different scenarios of R-parity violation are discussed. The possible contribution of R-parity-violating Yukawa couplings in processes involving virtual supersymmetric particles and the resulting constraints are reviewed. Finally, direct production of supersymmetric particles and their decays in the presence of R-parity-violating couplings is discussed together with a survey of existing constraints from collider experiments., Comment: 263 pages, latex, updated version submitted to Physics Reports

We study the LHC signatures of TeV scale vectorlike quarks $b'$, $t'$ and $\chi$ with electromagnetic charges -1/3, 2/3 and 5/3 that appear in many beyond the standard model (BSM) extensions. We consider warped extra-dimensional models and analyze the phenomenology of such vectorlike quarks that are the custodial partners of third generation quarks. In addition to the usually studied pair-production channels which depend on the strong coupling, we put equal emphasis on single production channels that depend on electroweak couplings and on electroweak symmetry breaking induced mixing effects between the heavy vectorlike quarks and standard model quarks. We identify new promising $gg$-initiated pair and single production channels and find the luminosity required for discovering these states at the LHC. For these channels, we propose a cut that allows one to extract the relevant electroweak couplings. Although the motivation is from warped models, we present many of our results model-independently., Comment: Published version. 40 pages, 19 figures, 12 tables. References added. Minor revisions

In the context of a simple five-dimensional (5D) model with bulk matter coupled to a brane-localized Higgs boson, we point out a new non-commutativity in the 4D calculation of the mass spectrum for excited fermion towers: the obtained expression depends on the choice in ordering the limits, N->infinity (infinite Kaluza-Klein tower) and epsilon->0 (epsilon being the parameter introduced for regularizing the Higgs Dirac peak). This introduces the physical question of which one is the correct order; we then show that the two possible orders of regularization (called I and II) are physically equivalent, as both can typically reproduce the measured observables, but that the one with less degrees of freedom (I) could be uniquely excluded by future experimental constraints. This conclusion is based on the exact matching between the 4D and 5D analytical calculations of the mass spectrum - via the regularizations of type I and II. Beyond a deeper insight into the Higgs peak regularizations, this matching also allows us to confirm the validity of the usual 5D mixed-formalism and to clarify the UV cut-off procedure. All the conclusions, deduced from regularizing the Higgs peak through a brane shift or a smoothed square profile, are expected to remain similar in realistic models with a warped extra-dimension., 29 pages, 2 tables

We consider the single chargino production at Tevatron $p \bar p \to \tilde \nu_i \to \tilde \chi^{\pm}_1 l_i^{\mp}$ as induced by the resonant sneutrino production via a dominant \RPV coupling of type $\l'_{ijk} L_i Q_j D_k^c$. Within a supergravity model, we study the three leptons final state. The comparison with the expected background demonstrate that this signature allows to extend the sensitivity on the \susyq mass spectrum beyond the present LEP limits and to probe the relevant \RPV coupling down to values one order of magnitude smaller than the most stringent low energy indirect bounds. The trilepton signal offers also the opportunity to reconstruct the neutralino mass in a model independent way with good accuracy., Comment: 4 pages

Using the full set of the LHC Higgs data from the runs at 7 and 8 TeV center of mass energies that have been released by the ATLAS and CMS collaborations, we determine the couplings of the Higgs particle to fermions and gauge bosons as well as its parity or CP composition. We consider ratios of production cross sections times decay branching fractions in which the theoretical (and some experimental) uncertainties as well as as some ambiguities from new physics cancel out. A fit of both the signal strengths in the various search channels that have been conducted, H -> Z Z, W W, gamma gamma, tau tau and b b, and their ratios shows that the observed ~126 GeV particle has couplings to fermions and gauge bosons that are Standard Model-like already at the 68% confidence level (CL). From the signal strengths in which the theoretical uncertainty is taken to be a bias, the particle is shown to be at most 68% CP-odd at the 99%CL and the possibility that it is a pure pseudoscalar state is excluded at the 4 sigma level when including both the experimental and theoretical uncertainties. The signal strengths also measure the invisible Higgs decay width which, with the same type of uncertainty analysis, is shown to be Gamma_H^inv / Gamma_H^SM < 0.52 at the 68%CL., 15 pages, 13 figures

We analyze the Minimal Supersymmetric extension of the Standard Model that we have after the discovery of the Higgs boson at the LHC, the hMSSM (habemus MSSM?), i.e. a model in which the lighter $h$ boson has a mass of approximately 125 GeV which, together with the non-observation of superparticles at the LHC, indicates that the SUSY-breaking scale $M_S$ is rather high, $M_S > 1$ TeV. We first demonstrate that the value $M_h \approx 125$ GeV fixes the dominant radiative corrections that enter the MSSM Higgs boson masses, leading to a Higgs sector that can be described, to a good approximation, by only two free parameters. In a second step, we consider the direct supersymmetric radiative corrections and show that, to a good approximation, the phenomenology of the lighter Higgs state can be described by its mass and three couplings: those to massive gauge bosons and to top and bottom quarks. We perform a fit of these couplings using the latest LHC data on the production and decay rates of the light $h$ boson and combine it with the limits from the negative search of the heavier $H,A$ and $H^\pm$ states, taking into account the current uncertainties., 1+12 pages, pdflatex, 7 figures

First, we study the fit of the Higgs boson rates, based on all the latest collider data, in the effective framework for any Extra-Fermion(s) [EF]. The best-fit results are presented in a generic formalism allowing to apply those for the test of any EF scenario. The variations of the fit with each one of the five fundamental parameters are described, and, the obtained fits can be better than in the Standard Model (SM). We show how the determination of the EF loop-contributions to the Higgs couplings with photons and gluons is relying on the knowledge of the top and bottom Yukawa couplings (affected by EF mixings); for determining the latter coupling, the relevance of the investigation of the Higgs production in association with bottom quarks is emphasized. In the instructive approximation of a single EF, we find that the constraints from the fit already turn out to be quite predictive, in both cases of an EF mixed or not with SM fermions, and especially when combined with the extra-quark (-lepton) mass bounds from direct EF searches at the LHC (LEP) collider. In the case of an unmixed extra-quark, non-trivial fit constraints are pointed out on the Yukawa couplings for masses up to ~200 TeV. In particular, we define the extra-dysfermiophilia, which is predicted at 68.27% C.L. for any single extra-quark (independently of its electric charge). Another result is that, among any components of SM multiplet extensions, the extra-quark with a -7/3 electric charge is the one preferred by the present Higgs fit., 27 pages, 10 figures. Subsection structure added and Higgs boson rates updated (in a separate Appendix) after the Moriond 2013 conference

Vector-Like (VL) quarks arise in the main alternatives to the supersymmetric extensions of the Standard Model (SM). Given the experimental possibility of a 125 GeV Higgs boson with rates significantly different from the SM expectations, it is motivating to study the effects of VL quarks on the Higgs boson cross sections and branching ratios. We perform a systematic search for the minimal field contents and gauge group representations of VL quarks able to significantly improve the fit of the measured Higgs rates, and simultaneously, to satisfy the direct constraints on VL quark masses as well as the electro-weak precision tests. In particular, large enhancements can be achieved in certain diphoton channels - as pointed out by both the ATLAS and CMS Collaborations - optimizing then the Higgs rate fit. This is a consequence of the introduction of VL quarks, with high electric charges of 8/3 or -7/3, which are exchanged in the Higgs-to-diphoton loop. Interestingly, the field contents and formal Higgs couplings obtained here are similar to those of scenarios in warped/composite frameworks arising from different motivations. The various exotic-charge quarks predicted, possibly below the TeV scale, might lead to a rich phenomenology soon at the LHC., Comment: 11 pages, 4 figures

Azatov, A. et al., We first build a minimal model of vectorlike quarks where the dominant Higgs boson production process at LHC-the gluon fusion-can be significantly suppressed, being motivated by the recent stringent constraints from the search for direct Higgs production over a wide Higgs mass range. Within this model, compatible with the present experimental constraints on direct Higgs searches, we demonstrate that the Higgs (h) production via a heavy vectorlike top-partner (t2) decay, pp→t2t¯2, t2→th, allows to discover a Higgs boson at the LHC and measure its mass, through the decay channels h→γγ or h→ZZ. We also comment on the recent hint in LHC data from a possible ∼125GeV Higgs scalar, in the presence of heavy vectorlike top quarks. © 2012 American Physical Society., The work of G. M. is supported by the Institut Universitaire de France as well as the ANR CPV-LFVLHC under Project No. NT09-508531 and TAPDMS under Project No. 09-JCJC-0146. D.K.G. acknowledges partial support from the Department of Science and Technology, India under the Grant No. SR/S2/HEP-12/2006.

In the scenario where only superpartners were produced at the Large Hadron Collider, how one could determine whether the supersymmetric model pointed out is 4-dimensional or higher-dimensional ? We propose and develop a series of tests for discriminating between a pure supersymmetry (SUSY) and a SUSY realized within the well-motivated warped geometry a la Randall-Sundrum (RS). Two of these tests make use of some different patterns arising in the squark/slepton mass spectrum. The other distinctive RS SUSY feature is the possibly larger (even dominant) Higgs boson decay branching ratios into sleptons, compared to pure SUSY. Techniques for pinning up the presence of soft SUSY breaking terms on the TeV-brane are also suggested, based on the analysis of stop pair production at the International Linear Collider. For all these phenomenological studies, we had first to derive the 4-dimensional (4D) effective couplings and mass matrices of the sfermions and Higgs bosons in RS SUSY. The localization of Higgs bosons, characteristic of RS, leads to singularities in their couplings which are regularized by the exchange contribution of infinite towers of Kaluza-Klein (KK) scalar modes with Dirichlet-Dirichlet boundary conditions. A general method is provided for this regularization, based on the completeness relation. The sfermion masses are obtained either from integrating out those specific KK towers or by treating their mixing effects. Finally, we show at the one-loop level how all quadratic divergences in the Higgs mass cancel out for any cut-off, due to 5D SUSY and to 5D anomaly cancellation; the analytical way followed here also allows a justification of the infinite KK summation required for the so-called KK regularization in 5D SUSY, which has motivated a rich literature.

Within the paradigm of warped extra dimensions, third generation quarks are expected to be the most sensitive to effects beyond the Standard Model. The anomalies observed at the LEP and Tevatron colliders in the forward-backward asymmetries of the bottom (A_FB^b) and top (A_FB^t) quarks can thus be seen as early signatures of warped extra-dimensional scenarios. We propose a realization of such a scenario, with a gauge custodial symmetry in the bulk, which allows to address simultaneously the A_FB^b anomaly and the discrepancies observed recently on A_FB^t at high top quark rapidities and ttbar invariant masses. We also show that the various phenomenological constraints arising from LEP, Tevatron and LHC can be satisfied within the considered model. The model predicts new features, induced by a Kaluza-Klein excitation of the gluon at a mass ~1.5-2 TeV, in top quark pair production at the 7 TeV LHC., 13 pages, 7 figures, new references and a note added on recent ATLAS results

In the framework of warped extra dimension models addressing the gauge hierarchy problem, we consider the Randall-Sundrum (RS) scenario under the usual hypothesis of a bulk custodial symmetry. It is shown in detail that there can exist large corrections to the Higgs boson vacuum expectation value (VEV) induced by mixings of the gauge bosons with their Kaluza-Klein (KK) excitations. The connection with electroweak precision tests is developed. A noteworthy result is that the correct treatment of the Higgs VEV leads to an increase of the lower limit at 95% C.L. on KK masses that can reach +30% (from usually accepted values). For a Higgs mass 120{

The CDF and D0 experiments have reported on the measurement of the forward-backward asymmetry of top quark pair production at the Tevatron and the result is that it is more than 2 standard deviations above the predicted value in the Standard Model. This has to be added to the longstanding anomaly in the forward-backward asymmetry for bottom quark production at LEP which is 3 standard deviations different from the Standard Model value. The discrepancy in the bottom asymmetry can be accounted for by the contributions of Kaluza-Klein excitations of electroweak gauge bosons at LEP in warped extra dimensional models in which the fermions are localized differently along the extra dimension so that the gauge interactions of heavy third generation fermions are naturally different from that of light fermions. In this paper, we show that it is more difficult to elaborate a model generating a significant top asymmetry in a similar way -- through exchanges of Kaluza-Klein gluons at the Tevatron -- due to the indirect constraints originating from precision electroweak data., 4 pages, 1 figure, published version

The Randall-Sundrum scenario with Standard Model fields in the bulk and a custodial symmetry is considered. We determine the several minimal quark representations allowing to address the anomalies in the forward-backward b-quark asymmetry A^b_FB, while reproducing the bottom and top masses via wave function overlaps. The calculated corrections of the Zbb coupling include the combined effects of mixings with both Kaluza-Klein excitations of gauge bosons and new b'-like states. It is shown that the mechanism, in which the left-handed doublet of third generation quarks results from a mixing on the UV boundary of introduced fields Q_1L and Q_2L, is necessary for phenomenological reasons. Within the obtained models, both the global fit of R_b with A^b_FB [at the various center of mass energies] and the fit of last precision electroweak data in the light fermion sector can simultaneously be improved significantly with respect to the pure Standard Model case, for M_KK = 3,4,5 TeV (first KK gauge boson) and a best-fit Higgs mass m_h > 115 GeV i.e. compatible with the LEP2 direct limit. The quantitative analysis of the oblique parameters S,T,U even shows that heavy Higgs mass values up to ~500 GeV may still give rise to an acceptable quality of the electroweak data fit, in contrast with the Standard Model. The set of obtained constraints on the parameter space, derived partly from precision electroweak data, is complementary of a future direct exploration of this parameter space at the LHC. In particular, we find that custodians, like b' modes, can be as light as ~1200 GeV i.e. a mass lying possibly in the potential reach of LHC., 24 pages, 8 figures. Added references, corrected typos and Higgs mass dependence discussion completed

The extra-dimensional model in which the bulk geometry is a slice of anti-de Sitter space is a particularly attractive extension of the Standard Model as it allows to address the gauge hierarchy problem, as well as the mass hierarchy prevailing among fermions. However, to allow for the masses of the Kaluza-Klein excitations of the known particles to be near the Terascale without conflicting with the high-precision electroweak data, one needs to promote the gauge symmetry to a left-right structure SU(2)_L x SU(2)_R x U(1) which incorporates a new quark b', the SU(2)_R doublet partner of the heavy top quark. We show that this new quark will contribute to the main production process of Higgs bosons at the LHC: the gluon-gluon fusion mechanism which proceeds through heavy quark triangular loops. In most of the parameter space in which the measured values of the heavy t,b quark masses are reproduced, the gg -> Higgs production cross section is significantly altered, even if the b' quark is too heavy to be directly accessible, m_b' > ~1TeV. Finally, we briefly discuss the new Higgs production and decay channels involving the b' quark., Latex file, 6 pages, 3 figures. Comments added, Higgs branching ratios calculated and interference modified

We study a purely leptonic signature of the Randall-Sundrum scenario with Standard Model fields in the bulk at LHC: the contribution from the exchange of Kaluza-Klein (KK) excitations of gauge bosons to the clear Drell-Yan reaction. We show that this contribution is detectable (even with the low luminosities of the LHC initial regime) for KK masses around the TeV scale and for sufficiently large lepton couplings to KK gauge bosons. Such large couplings can be compatible with ElectroWeak precision data on the Zff coupling in the framework of the custodial O(3) symmetry recently proposed, for specific configurations of lepton localizations (along the extra dimension). These configurations can simultaneously reproduce the correct lepton masses, while generating acceptably small Flavour Changing Neutral Current (FCNC) effects. This LHC phenomenological analysis is realistic in the sense that it is based on fermion localizations which reproduce all the quark/lepton masses plus mixing angles and respect FCNC constraints in both the hadron and lepton sectors., 15 pages, 6 Figures, Latex file

In the Minimal Supersymmetric Standard Model with bilinear R-parity violation, only one neutrino eigenstate acquires a mass at tree level, consequently experimental data on neutrinos cannot be accommodated at tree level. We show that in the Next-to-Minimal extension, where a gauge singlet superfield is added to primarily address the so-called $\mu$-problem, it is possible to generate two massive neutrino states at tree level. Hence, the global three-flavour neutrino data can be reproduced at tree level, without appealing to loop dynamics which is vulnerable to model-dependent uncertainties. We give analytical expressions for the neutrino mass eigenvalues and present examples of realistic parameter choices., Comment: 9 pages, 2 figures; further clarifications added, to appear in PLB

We consider the Next to Minimal Supersymmetric Standard Model (NMSSM) which provides a natural solution to the so-called mu problem by introducing a new gauge-singlet superfield S. We realize that a new mechanism of neutrino mass suppression, based on the R-parity violating bilinear terms mu_i L_i H_u mixing neutrinos and higgsinos, arises within the NMSSM, offering thus an original solution to the neutrino mass problem (connected to the solution for the mu problem). We generate realistic (Majorana) neutrino mass values without requiring any strong hierarchy amongst the fundamental parameters, in contrast with the alternative models. In particular, the ratio |mu_i/mu| can reach about 10^-1, unlike in the MSSM where it has to be much smaller than unity. We check that the obtained parameters also satisfy the collider constraints and internal consistencies of the NMSSM. The price to pay for this new cancellation-type mechanism of neutrino mass reduction is a certain fine tuning, which get significantly improved in some regions of parameter space. Besides, we discuss the feasibility of our scenario when the R-parity violating bilinear terms have a common origin with the mu term, namely when those are generated via a VEV of the S scalar component from the couplings lambda_i S L_i H_u. Finally, we make comments on some specific phenomenology of the NMSSM in the presence of R-parity violating bilinear terms., 21 pages, 5 figures, Latex file

We consider the simple extension of the Standard Model in which an additional right handed neutrino propagates along a flat extra dimension, while the Standard Model fields are confined on a 3-brane. The fifth dimension is $S^1/Z_2$ orbifold compactified. In this scenario, the neutrino mass can be naturally suppressed. By studying systematically the fundamental parameter space, we show that the strong phenomenological constraints on mixing angles between active and sterile neutrinos (especially those derived from the SNO experiment data) do not conflict with the possibility of generating a realistic neutrino mass spectrum. As a second step, we explore the possibility of a successful leptogenesis through the decays of the Kaluza-Klein excitations of the right handed neutrino., Comment: 16 pages, 2 ps figures

Scenarios based on the existence of large or warped (Randall-Sundrum model) extra dimensions have been proposed for addressing the long standing puzzle of gauge hierarchy problem. Within the contexts of both those scenarios, a novel and original type of mechanism generating small (Dirac) neutrino masses, which relies on the presence of additional right-handed neutrinos that propagate in the bulk, has arisen. The main objective of the present study is to determine whether this geometrical mechanism can produce reasonable neutrino masses also in the interesting multi-brane extensions of the Randall-Sundrum model. We demonstrate that, in some multi-brane extensions, neutrino masses in agreement with all relevant experimental bounds can indeed be generated but at the price of a constraint (stronger than the existing ones) on the bulk geometry, and that the other multi-brane models even conflict with those experimental bounds., 29 pages, 3 figures, Latex file. References added, study extended

We present a general study of a three neutrino flavour transition model based on the supersymmetric interactions which violate R-parity. These interactions induce flavour violating scattering reactions between solar matter and neutrinos. The model does not contain any vacuum mass or mixing angle for the first generation neutrino. Instead, the effective mixing in the first generation is induced via the new interactions. The model provides a natural interpretation of the atmospheric neutrino anomaly, and is consistent with reactor experiments. We determine all R-parity violating couplings which can contribute to the effective neutrino oscillations, and summarize the present laboratory bounds. Independent of the specific nature of the (supersymmetric) flavour violating model, the experimental data on the solar neutrino rates and the recoil electron energy spectrum are inconsistent with the theoretical predictions. The confidence level of the $\chi^2$-analysis ranges between $\sim 10^{-4}$ and $\sim 10^{-3}$. The incompatibility, is due to the new SNO results, and excludes the present model. We conclude that a non-vanishing vacuum mixing angle for the first generation neutrino is necessary in our model. We expect this also to apply to the solutions based on other flavour violating interactions having constraints of the same order of magnitude., Comment: 17 pages, Latex file

We study a multi-localization model for charged leptons and neutrinos, including the possibility of a see-saw mechanism. This framework offers the opportunity to allow for realistic solutions in a consistent model without fine-tuning of parameters, even if quarks are also considered. Those solutions predict that the large Majorana mass eigenvalues for right-handed neutrinos are of the same order of magnitude, although this almost common mass can span a large range (bounded from above by $\sim 10^{12}{\rm GeV}$). The model also predicts Majorana masses between $\sim 10^{-2}{\rm eV}$ and $\sim 5 \ 10^{-2}{\rm eV}$ for the left-handed neutrinos, both in the normal and inverted mass hierarchy cases. This mass interval corresponds to sensitivities which are reachable by proposed neutrinoless double $\beta$ decay experiments. The preferred range for leptonic mixing angle $\theta_{13}$ is: $10^{-2} \lesssim \sin \theta_{13} \lesssim 10^{-1}$, but smaller values are not totally excluded by the model., Comment: 36 pages, 8 figures

Based on the R-parity violation option of the minimal supersymmetric Standard Model, we examine the scenario where the massive gravitino, relic from the hot big-bang, is the lightest supersymmetric particle and can decay through one or several of the trilinear R-parity violating interactions. We calculate the rates of the gravitino decay via the various three-body decay channels with final states involving three quarks and/or leptons. By taking into account the present constraints on the trilinear R-parity violating coupling constants and assuming the gravitino and scalar superpartner masses do not exceed ${\cal O}(10TeV)$, it turns out that the gravitinos could easily have decayed before the present epoch but not earlier than the big-bang nucleosynthesis one. Therefore, the considered scenario would upset the standard big-bang nucleosynthesis and we conclude that it does not seem to constitute a natural solution for the cosmological gravitino problem., Comment: 22 pages, Latex file, 5 figures

The resonant production of sneutrinos at the LHC via the R-parity violating couplings $\l '_{ijk} L_i Q_j D^c_k$ is studied through its three-leptons signature. A detailed particle level study of signal and background is performed using a fast simulation of the ATLAS detector. Through the full reconstruction of the cascade decay, a model-independent and precise measurement of the masses of the involved sparticles can be performed. Besides, this signature can be detected for a broad class of supersymmetric models, and for a wide range of values of several $\l '_{ijk}$ coupling constants. Within the MSSM, the production of a 900 GeV sneutrino for $\lambda^{\prime}_{211}>0.05$, and of a 350 GeV sneutrino for $\lambda^{\prime}_{211}>0.01$ can be observed within the first three years of LHC running., Comment: 33 pages, 19 figures, Latex file

We examine the effect of the R parity odd renormalizable interactions on flavor non-diagonal rates and CP violation asymmetries in the production of slepton pairs at $e^- - e^+$ leptonic colliders, for center of mass energies spanning the interval from the Z-boson pole up to 1000 GeV. The lepton number violating interactions, associated with the lepton number violating coupling constants, are assumed to incorporate CP odd complex phases. The flavor changing rates are controlled by tree level amplitudes and quadratic products of different R parity violating coupling constants and the CP asymmetries by interference terms between tree and loop level amplitudes and quartic products. The consideration of loop amplitudes is restricted to the photon and Z-boson vertex corrections. We present numerical results using a family and species independent mass parameter, $\tilde m$, for all the scalar superpartners and making simple assumptions for the family dependence of the R parity odd coupling constants. The flavor non-diagonal rates, $\s_{JJ'}$, vary in the range, $(��/0.1)^4 2 - 20$ fbarns, as one spans the interval of center of mass energies from the Z-boson pole up to 1000 GeV. For sleptons masses, $\tilde m> 150 $ GeV, these observables could be of use at NLC energies to set useful bounds on the R parity odd coupling constants. The values of the asymmetries, vary from a few to a few tens of $10^{-3}$., Latex File. 14 pages. 3 postscript figures. 1 table

Among the motivations for a theory beyond the Standard Model (SM) of particle physics, the existence of new scales above the TeV implies the question of the stability of the electroweak scale with respect to radiative corrections to the Higgs boson mass. An attractive way to protect the electroweak scale is to build scenarii with q Spacelike Extra Dimensions (SED) compactified on a torus where the (4+q)D gravity scale is reduced to the TeV, through a large compactified volume, and acts as a cut-off for the SM. These models suffer from a problem of stabilization of the large compactification radii. Within the other paradigm with a small warped SED, the Higgs field is in general localized at a boundary of the SED (TeV-brane) where the gravity scale is redshifted to the TeV by a warp factor. If the SM gauge bosons and fermions propagate into the warped SED, one can generate the mass hierarchy for fermions. It is thus crucial to treat carefully the TeV-brane localized masses for such fermions, which is done in the literature by applying a regularization process suffering from a lack of consistency and more importantly being useless, as we demonstrate in detail in the present thesis. The first part of the thesis is devoted to the treatment of brane localized mass terms for 5D fermions, which requires the introduction of new Lagrangian terms at the SED boundaries, similar to the Gibbons-Hawking terms in gravity. The second part consists in applying different methods (function/distribution fields, 4D/5D calculations, etc) to various brane localized terms (kinetic terms, Majorana masses, etc), as well as a generalization to several classified models (flat/warped dimensions, intervalle/orbifold, etc). In the third part, we propose to compactify a flat SED on a star/rose graph with a large number of identical small leaves/petals. We obtain a compactified space with a large volume without a large compactification length to stabilize. We use the approach of 5D fermions to build a toy model of small Dirac neutrino masses (brane localized left-handed neutrinos and bulk right-handed ones)., Parmi les motivations pour une théorie au-delà du Modèle Standard (MS) de la physique des particules, l'existence de nouvelles échelles au-dessus du TeV pose la question de la stabilité de l'échelle électrofaible au travers des corrections radiatives à la masse du boson de Higgs. Une voie attrayante pour protéger l'échelle électrofaible est de construire des scenarii avec q Dimensions Spatiales Supplémentaires (DSS) compactifiées sur un tore où l'échelle de gravité à (4+q)D est ramenée au TeV, grâce à un grand volume compactifié, et agit comme une échelle de coupure pour le MS. Ces modèles souffrent d'un problème de stabilisation des grands rayons de compactification. Dans l'autre paradigme avec une petite DSS courbe, le champ de Higgs est en général localisé sur un bord de la DSS (TeV-brane) où l'échelle de gravité y est ramenée au TeV par un facteur de courbure. Si les bosons de jauge et les fermions du MS se propagent dans la DSS courbe, on peut générer la hiérarchie de masse des fermions. Il est donc crucial de traiter soigneusement les masses localisées sur la TeV-brane pour de tels fermions, ce qui est fait dans la littérature par une procédure de régularisation manquant de rigueur et surtout s'avérant inutile, comme nous le démontrons en détails dans cette thèse. La première phase de la thèse est dédiée au traitement de termes de masse localisés pour les fermions à 5D, ce qui implique d'introduire de nouveaux termes dans le lagrangien aux bords de la DSS courbe, analogues aux termes de Gibbons-Hawking en gravité. La deuxième phase consiste en une application de différentes méthodes (champs fonctions/distributions, calculs 4D/5D, etc) à divers termes branaires (termes cinétiques, masses de Majorana, etc), ainsi qu'en une généralisation à plusieurs modèles (dimensions plates/courbes, intervalle/orbifold, etc) classifiés. Dans une troisième phase, nous proposons de compactifier une DSS plate sur un graphe étoile/rose avec un grand nombre de petites branches/pétales identiques. On obtient un espace compactifié avec un grand volume sans une grande longueur de compactification à stabiliser. On utilise l'approche des fermions à 5D pour construire un modèle jouet de petites masses de Dirac pour les neutrinos (neutrinos gauches branaires et droits dans le bulk).

Almost two decades ago, the paradigm of extra-dimensional models addressing the gauge hierarchy problem attracted much attention through the elegant proposals of large, flat extra dimensions (EDs) - the Arkani-Hamed-Dimopoulos-Dvali or ADD model - and warped EDs - the Randall-Sundrum or RS model. In this thesis, we discuss several models inspired from such extra-dimensional scenarios. We start by introducing some key elements of field theory in five space-time dimensions and showing how such scenarios provide a solution to the hierarchy problem. Afterwards, in a first part of this work, we adopt a bottom-up approach and study several models containing Vector-Like Fermions (VLFs), which are typically predicted in ED frameworks. We show how adding Vector-Like Quarks (VLQs) to the Standard Model (SM) allows one to simultaneously explain the anomalies in the (i) b-quark forward-backward asymmetry measured at the Large Electron-Positron collider (LEP) and (ii) the tth production cross section measured at the Large Hadron Collider (LHC). Using the so-called Higgs decay ratios, we also estimate the sensitivity of the upgraded LHC, the High-Luminosity LHC, to the presence of VLQs. Then, we consider a Two-Higgs Doublet Model (2HDM) extended with Vector-Like Leptons (VLLs) in order to fit the mysterious 750 GeV excess observed at LHC in late 2015. Within a similar model, we also explain the Dark Matter (DM) abundance in the Universe, our DM candidate being a neutral VLL, which is rendered stable by a suitable Z2 symmetry. Later on, in a second part of the thesis, we focus on the more concrete warped ED scenario endowed with a bulk custodial symmetry, which protects the model from large electroweak (EW) corrections. In this framework, we first interpret the 2 TeV diboson bump observed at LHC in 2015 as a superposition of Kaluza-Klein (KK) gauge bosons produced in the s-channel. Afterwards, we study the phenomenology of the mixed Higgs-radion scalar sector of the aforementioned model. In particular, we estimate the sensitivity of the LHC and of a future electron-positron collider (the International Linear Collider - ILC) to the existence of a radion via its production in association with a Z boson.; Il y a près de deux décennies, l'utilisation des modèles à dimensions supplémentaires pour résoudre le problème de hiérarchie des théories de jauge a reçu beaucoup d'attention, au travers d'élégantes propositions : des dimensions supplémentaires (DS) étendues et plates - le modèle d'Arkani-Hamed-Dimopoulos-Dvali, ou ADD - ainsi que des DS courbées - le modèle de Randall-Sundrum, ou RS. Dans cette thèse, nous discutons plusieurs modèles inspirés de tels scénarios extra-dimensionnels. Pour commencer, nous introduisons des éléments-clés de la théorie des champs en cinq dimensions, et nous montrons comment de tels scénarios apportent une réponse au problème de hiérarchie. Ensuite, dans une première partie, nous adoptons une approche ``de bas en haut'' et étudions plusieurs modèles contenant des fermions vectoriels (FV), prédits génériquement dans les modèles de DS. Nous montrons qu'en ajoutant des quarks vectoriels (QV) au Modèle Standard (MS), on peut expliquer en même temps les anomalies (i) d'asymétrie avant-arrière des quarks b, mesurée au Large Electron-Positron collider (LEP) et (ii) de section efficace de production de tth mesurée au Large Hadron Collider (LHC). En utilisant des rapports de taux de désintégration du Higgs, nous estimons aussi la sensibilité du LHC amélioré, le LHC à haute luminosité, à la présence de QV. Puis nous considérons un modèle à deux doublets de Higgs (2HDM), accompagné de leptons vectoriels (LV) pour expliquer le mystérieux excès à 750 GeV observé au LHC fin 2015. Dans un modèle similaire, nous expliquons également l'abondance de matière sombre (MS) dans l'Univers, notre candidat pour la MS étant un LV neutre, stabilisé par une symétrie Z2 appropriée. Par la suite, dans une deuxième partie de la thèse, nous nous penchons sur le scénario plus concret des DS courbées dotées d'une symétrie custodiale dans l'espace cinq-dimensionnel, qui protège le modèle vis-à-vis de larges corrections électrofaibles. Dans ce cadre, nous interprétons tout d'abord la bosse à deux bosons observée à 2 TeV au LHC comme une superposition de bosons de jauge de Kaluza-Klein, produits en canal s. Dans un deuxième temps, nous étudions la phénoménologie du secteur scalaire du modèle susdit, qui mêle le Higgs et le radion. En particulier, nous estimons la sensibilité du LHC et d'un futur collisionneur électron-positron (l'International Linear Collider - ILC) à l'existence d'un radion, via la production de celui-ci en association avec un boson Z.