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Mariana Frank

Publications and source records attributed to Mariana Frank.

At least 55 records · Page 3Linked to original sources

Differentiating $U(1)^\prime$ supersymmetric models with right sneutrino and neutralino dark matter

We perform a detailed analysis of dark matter signals of supersymmetric models containing an extra $U(1)^\prime$ gauge group. We investigate scenarios in which either the right sneutrino or the lightest neutralino are phenomenologically acceptable dark matter candidates and we explore the parameter spaces of different supersymmetric realisations featuring an extra $U(1)^\prime$. We impose consistency with low energy observables, with known mass limits for the superpartners and $Z^\prime$ bosons, as well as with Higgs boson signal strengths, and we moreover verify that predictions for the anomalous magnetic moment of the muon agree with the experimental value and require that the dark matter candidate satisfies the observed relic density and direct and indirect dark matter detection constraints. For the case where the sneutrino is the dark matter candidate, we find distinguishing characteristics among different $U(1)^\prime$ mixing angles. If the neutralino is the lightest supersymmetric particle, its mass is heavier than that of the light sneutrino in scenarios where the latter is a dark matter candidate, the parameter space is less restricted and differentiation between models is more difficult. We finally comment on the possible collider tests of these models.

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Dark Matter and Collider Studies in the Left-Right Symmetric Model with Vector-Like Leptons

In the context of a left-right symmetric model, we introduce one full generation of vectorlike lepton doublets (both left and right-handed) together with their mirror doublets. We show that the lightest vectorlike neutrino in the model is right-handed, and can serve as the dark matter candidate. We find that the relic density, as well as the direct and indirect DM detection bounds, are satisfied for a large range of the parameter space of the model. In accordance with the parameter space, we then explore the possibility of detecting signals of the model at both the LHC and the ILC, in the pair production of the associated vectorlike charged leptons which decay into final states including dark matter. A comprehensive analysis of signal and backgrounds shows that the signals at the ILC, especially with polarized beams are likely to be visible for light vectorlike leptons, even with low luminosity, rendering our model highly predictable and experimentally testable.

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Top and bottom partners, Higgs boson on the brane, and the tth signal

Current LHC results indicate a possible enhancement in the production of Higgs bosons in association with top quarks (tth) over the Standard Model (SM) expectations, suggesting an increase in the top Yukawa coupling. To explain these results, we study the effect of adding to the SM a small set of vector-like partners of the top and bottom quarks with masses of order ~1 TeV. We consider Yukawa coupling matrices with vanishing determinant and show that then, Higgs production through gluon fusion is not affected by deviations in the top quark Yukawa coupling, and in fact depends only on deviations in the bottom quark Yukawa coupling. We call this scenario the "Brane Higgs Limit", as it can emerge naturally in models of warped extra-dimensions with all matter fields in the bulk, except the Higgs (although it could also occur in 4D scenarios with vector-like quarks and special flavor symmetries forcing the vanishing of the Yukawa determinants). We show that the scenario is highly predictive for all Higgs production/decay modes, making it easily falsifiable, maybe even at the LHC RUN 2 with higher luminosity.

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Resonant slepton production and right sneutrino dark matter in left-right supersymmetry

Right-handed sneutrinos are natural components of left-right symmetric supersymmetric models where the gauge sector is extended to include right-handed weak interactions. Unlike in other models where right-handed sneutrinos are gauge singlets, here the right sneutrino is part of a doublet and could be a dark matter candidate whose annihilation proceeds via gauge interactions. We investigate this possibility, and find that relic density, low-energy observable and direct supersymmetry search constraints can be satisfied when the lightest supersymmetric particle is a right-handed sneutrino. We introduce benchmarks for left-right supersymmetric realizations where either a sneutrino or a neutralino is the lightest superpartner. We then study the LHC signals arising through resonant right-handed slepton production via a $W_R$ gauge-boson exchange that lead to final states enriched in leptons, additionally containing a large amount of missing transverse momentum, and featuring a low jet multiplicity. We find that such a resonant production would boost the chances of discovering these weakly interacting supersymmetric particles for a mass range extending beyond 1 TeV already with a luminosity of 100 fb$^{-1}$. Finally, we compare sneutrino versus neutralino scenarios, and comment on differences with other sneutrino dark matter models.

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Bulk Higgs and the 750 GeV diphoton signal

We consider scenarios of warped extra-dimensions with all matter fields in the bulk and in which both the hierarchy and the flavor puzzles of the Standard Model are addressed. The simplest extra dimensional extension of the Standard Model Higgs sector, i.e a 5D bulk Higgs doublet, can be a natural and simple explanation to the 750 GeV excess of diphotons hinted at the LHC, with the resonance responsible for the signal being the lightest CP odd excitation coming from the Higgs sector. No new matter content is invoked, the only new ingredient being the presence of (positive) brane localized kinetic terms associated to the 5D bulk Higgs, which allow to reduce the mass of the lightest CP odd Higgs excitation to 750 GeV. Production and decay of this resonance can naturally fit the observed signal when the mass scale of the rest of extradimensional resonances is of order 1 TeV.

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Probing Higgs-radion mixing in warped models through complementary searches at the LHC and the ILC

We consider the Higgs-radion mixing in the context of warped space extra dimensional models with custodial symmetry and investigate the prospects of detecting the mixed radion. Custodial symmetries allow the Kaluza-Klein excitations to be lighter, and protect Zbb to be in agreement with experimental constraints. We perform a complementary study of discovery reaches of the Higgs-radion mixed state at the 13 and 14 TeV LHC and at the 500 and 1000 GeV ILC. We carry out a comprehensive analysis of the most significant production and decay modes of the mixed radion in the 80 GeV - 1 TeV mass range, and indicate the parameter space that can be probed at the LHC and the ILC. There exists a region of the parameter space which can be probed, at the LHC, through the diphoton channel even for a relatively low luminosity of 50 fb^{-1}. The reach of the 4-lepton final state, in probing the parameter space is also studied in the context of 14 TeV LHC, for a luminosity of 1000 fb^{-1}. At the ILC, with an integrated luminosity of 500 fb^{-1}, we analyze the Z-radion associated production and the WW fusion production, followed by the radion decay into bb and W+W-. The WW fusion production is favored over the Z-radion associated channel in probing regions of the parameter space beyond the LHC reach. The complementary study at the LHC and the ILC is useful both for the discovery of the radion and the understanding of its mixing sector.

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Flavor-changing decays of the top quark in 5D warped models

We study flavor changing neutral current decays of the top quark in the context of general warped extra dimensions, where the five dimensional metric is slightly modified from 5D anti-de-Sitter (AdS$_5$). These models address the Planck-electroweak hierarchies of the Standard Model $and$ can obey all the low energy flavor bounds and electroweak precision tests, while allowing the scale of new physics to be at the TeV level, and thus within the reach of the LHC at Run II. We perform the calculation of these exotic top decay rates for the case of a bulk Higgs, and thus include in particular the effect of the additional Kaluza-Klein (KK) Higgs modes running in the loops, along with the usual KK fermions and KK gluons.

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Higgs boson production and decay in 5D warped models

We calculate the production and decay rates of the Higgs boson at the LHC in the context of general 5 dimensional (5D) warped scenarios with a spacetime background modified from the usual $AdS_5$, with SM fields propagating in the bulk. We extend previous work by considering the full flavor structure of the SM, and thus including all possible flavor effects coming from mixings with heavy fermions. We proceed in three different ways, first by only including two complete Kaluza-Klein (KK) levels ($15\times15$ fermion mass matrices), then including three complete KK levels ($21\times21$ fermion mass matrices) and finally we compare with the effect of including the infinite (full) KK towers. We present numerical results for the Higgs production cross section via gluon fusion and Higgs decay branching fractions in both the modified metric scenario and in the usual Randall-Sundrum metric scenario.

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Neutrino Dark Matter in the Higgs Triplet Model

We analyze the effects of introducing vector-like leptons in the Higgs Triplet Model providing the lightest vector-like neutrino as a Dark Matter candidate. We explore the effect of the relic density constraint on the mass and Yukawa coupling of dark matter, as well as calculate the cross sections for indirect and direct dark matter detection. We show our model predictions for the neutrino and muon fluxes from the Sun, and the restrictions they impose on the parameter space. We show that this model, with a restricted parameter space, is completely consistent with dark matter constraints, and indicate the resulting mass region for the dark matter.

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Dark Matter in the Higgs Triplet Model

The inability to predict neutrino masses and the existence of the dark matter are two essential shortcomings of the Standard Model. The Higgs Triplet Model provides an elegant resolution of neutrino masses via the seesaw mechanism. We show here that introducing vectorlike leptons in the model also provides a resolution to the problem of dark matter. We investigate constraints, including the invisible decay width of the Higgs boson and the electroweak precision variables, and impose restrictions on model parameters. We analyze the effect of the relic density constraint on the mass and Yukawa coupling of dark matter. We also calculate the cross sections for indirect and direct dark matter detection and show our model predictions for the neutrino and muon fluxes from the Sun, and the restrictions they impose on the parameter space. With the addition of vectorlike leptons, the model is completely consistent with dark matter constraints, in addition to improving electroweak precision and doubly charged mass restrictions, which are rendered consistent with present experimental data.

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Fermion Masses and Mixing in General Warped Extra Dimensional Models

We analyze fermion masses and mixing in a general warped extra dimensional model, where all the Standard Model (SM) fields, including the Higgs, are allowed to propagate in the bulk. In this context, a slightly broken flavor symmetry imposed universally on all fermion fields, without distinction, can generate the full flavor structure of the SM, including quarks, charged leptons and neutrinos. For quarks and charged leptons, the exponential sensitivity of their wave-functions to small flavor breaking effects yield naturally hierarchical masses and mixing as it is usual in warped models with fermions in the bulk. In the neutrino sector, the exponential wave-function factors can be flavor-blind and thus insensitive to the small flavor symmetry breaking effects, directly linking their masses and mixing angles to the flavor symmetric structure of the 5D neutrino Yukawa couplings. The Higgs must be localized in the bulk and the model is naturally more successful in generalized warped scenarios where the metric background solution is different than $AdS_5$. We study these features in two simple frameworks, flavor complimentarily, and flavor democracy, which provide specific predictions and correlations between quarks and leptons, testable as more precise data in the neutrino sector becomes available.

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Probing the light radion through diphotons at the Large Hadron Collider

A radion in a scenario with a warped extra dimension can be lighter than the Higgs boson, even if the Kaluza-Klein excitation modes of the graviton turn out to be in the multi-TeV region. The discovery of such a light radion would be gateway to new physics. We show how the two-photon mode of decay can enable us to probe a radion in the mass range 60 - 110 GeV. We take into account the diphoton background, including fragmentation effects, and include cuts designed to suppress the background to the maximum possible extent. Our conclusion is that, with an integrated luminosity of 3000 $\rm fb^{-1}$ or less, the next run of the Large Hadron Collider should be able to detect a radion in this mass range, with a significance of 5 standard deviations or more.

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Left-right supersymmetry after the Higgs boson discovery

We perform a thorough analysis of the parameter space of the minimal left-right supersymmetric model in agreement with the LHC data. The model contains left- and right-handed fermionic doublets, two Higgs bidoublets, two Higgs triplet representations, and one singlet, insuring a charge-conserving vacuum. We impose the condition that the model complies with the experimental constraints on supersymmetric particles masses and on the doubly-charged Higgs bosons, and require that the parameter space of the model satisfy the LHC data on neutral Higgs signal strengths at $2σ$. We choose benchmark scenarios by fixing some basic parameters and scanning over the rest. The LSP in our scenarios is always the lightest neutralino. We find that the signals for $H\to γγ$ and $H \to VV^\star$ are correlated, while $H \to b \bar b$ is anti-correlated with all the other decay modes, and also that the contribution from singly-charged scalars dominate that of the doubly-charged scalars in $H\to γγ$ and $H \to Zγ$ loops, contrary to Type-II seesaw models. We also illustrate the range for mass spectrum of the LRSUSY model in light of planned measurements of the branching ratio of $H\to γγ$ to 10% level.

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Light Neutralino Dark Matter in $U(1)^\prime$ models

We analyze the prospects for light neutralino dark matter in the minimal supersymmetric model extended by a $U(1)$ gauge group. We allow the neutralino to be an arbitrary admixture of singlet and doublet higgsinos, as well as of the three gauginos, and we require agreement with the data from the direct and indirect dark matter detection experiments, while maintaining consistency of the model with the relic density and with the recent Higgs data from the LHC. The constraints have implications for the structure of the lightest neutralino as a dark matter candidate, indicating that it is largely singlino, and its mass can be as light as $\sim 20 $ GeV.

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Unified Flavor Symmetry from warped dimensions

We propose a scenario which accommodates all the masses and mixings of the SM fermions in a model of warped extra-dimensions with all matter fields in the bulk. In this scenario, the same flavor symmetric structure is imposed on all the fermions of the Standard Model (SM), including neutrinos. Due to the exponential sensitivity on bulk fermion masses, a small breaking of the symmetry can be greatly enhanced and produce seemingly un-symmetric hierarchical masses and small mixing angles among the charged fermion zero-modes (SM quarks and charged leptons) and wash-out the obvious effects of the symmetry. With the Higgs field leaking into the bulk, and Dirac neutrinos sufficiently localized towards the UV boundary, the neutrino mass hierarchy and flavor structure will still be largely dominated by the fundamental flavor structure. The neutrino sector would then reflect the fundamental flavor structure, whereas the quark sector would probe the effects of the flavor symmetry breaking sector. As an example, we explore these features in the context of a family permutation symmetry imposed in both quark and lepton sectors.

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Vector Quarks in the Higgs Triplet Model

We analyze the effects of introducing vector fermions in the Higgs Triplet Model. In this scenario, the model contains, in addition to the Standard Model particle content, one triplet Higgs representation, and a variety of vector-like fermion states, including singlet, doublet, and triplet states. We investigate the electroweak precision variables and impose restrictions on model parameters. We show that, for some representations, introducing vector quarks significantly alters the constraints on the mass of the doubly charged Higgs boson, bringing it in closer agreement with experimental constraints. We also study the effects of introducing the vector-like fermions on neutral Higgs phenomenology, in particular on the loop-dominated decays H -> gamma gamma and H -> Z gamma, and the restrictions they impose on the parameter space.

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Higgs data confronts Sequential Fourth Generation Fermions in the Higgs Triplet Model

We investigate the effect of introducing a sequential generation of chiral fermions in the Higgs Triplet Model with nontrivial mixing between the doublet and triplet Higgs. We use the available LHC data for Higgs boson production and decay rates, the constraints on the fourth generation masses, and impose electroweak precision constraints from the S, T and U parameters. Our analysis shows that an SM-like Higgs boson state at ~125 GeV can be accommodated in the Higgs Triplet Model with four generations, and thus, that four generations survive collider and electroweak precision constraints in models beyond SM.

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Dark Matter from Conformal Sectors

We show that a conformal-invariant dark sector, interacting conformally with the Standard Model (SM) fields through the Higgs portal, provides a viable framework where cold dark matter (CDM) and invisible Higgs decays can be addressed concurrently. Conformal symmetry naturally subsumes the Z_2 symmetry needed for stability of the CDM. It also guarantees that the weaker the couplings of the dark sector fields to the SM Higgs field, the smaller the masses they acquire through elektroweak breaking. The model comfortably satisfies the bounds from Large Hadron Collider (LHC) and Planck Space Telescope (Planck 2013).

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