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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Form invariance and symmetry in the neutrino mass matrix

We present the general form of the unitary matrices keeping invariant the Majorana neutrino mass matrix of specific texture suitable for explaining oscillation data. In the case of the tri-bimaximal pattern with two degenerate masses, we give a specific realization of the underlying U(1) symmetry which can be uplifted to a symmetry in a complete theory including charged leptons. For this, we present a model with three light SM-like Higgs doublets and one heavy Higgs triplet and find that one can accommodate the hierarchy of the charged-lepton masses. The lepton mass spectrum can also be achieved in another model extending the SM with three SM-singlet scalars transforming nontrivially under the flavor symmetry. We discuss how such a model has room for generating enough baryon asymmetry through leptogenesis in the framework of type-I and -II seesaw mechanisms.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Supersymmetric type-III seesaw mechanism: Lepton flavor violating decays and dark matter

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 24 superfields. The fermionic part of the SU(2) triplet contained in the 24 is responsible for the type-III seesaw, which is used to explain the observed neutrino masses and mixings. Complete copies of 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 electroweak scale using full 2-loop renormalization group equations. We show that the resulting spectrum can be quite different compared to the usual minimal Supergravity spectrum. We discuss how this might be used to obtain information on the seesaw scale from mass measurements. Constraints on the model space due to limits on lepton flavour violating decays are discussed. The main constraints come from the bounds on {mu}{yields}e{gamma} but there are also regions where the decay {tau}{yields}{mu}{gamma} gives stronger constraints. We also calculate the regions allowed by the dark matter constraint. For the sake of completeness, we compare our results with those for the supersymmetric seesaw type II and, to some extent, with type I.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Measurable neutrino mass scale in A{sub 4}xSU(5)

We propose a supersymmetric A{sub 4}xSU(5) model of quasidegenerate neutrinos which predicts the effective neutrino mass m{sub ee} relevant for neutrinoless double beta decay to be proportional to the neutrino mass scale, thereby allowing its determination approximately independently of unknown Majorana phases. Such a natural quasidegeneracy is achieved by using A{sub 4} family symmetry (as an example of a non-Abelian family symmetry with real triplet representations) to enforce a contribution to the neutrino mass matrix proportional to the identity. Tribimaximal neutrino mixing as well as quark CP violation with {alpha}{approx_equal}90 deg. d a leptonic CP phase {delta}{sub MNS{approx_equal}}90 deg. arise from the breaking of the A{sub 4} family symmetry by the vacuum expectation values of four 'flavon' fields pointing in specific postulated directions in flavor space.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Neutrino masses and mixing from S{sub 4} flavor twisting

We discuss a neutrino mass model based on the S{sub 4} discrete symmetry where the symmetry breaking is triggered by the boundary conditions of the bulk right-handed neutrino in the fifth spacial dimension. The three generations of the left-handed lepton doublets and the right-handed neutrinos are assigned to be the triplets of S{sub 4}. The magnitudes of the lepton mixing angles, especially the reactor angle, are related to the neutrino mass patterns, and the model will be tested in future neutrino experiments, e.g., an early discovery of the reactor angle favors the normal hierarchy. For the inverted hierarchy, the lepton mixing is predicted to be almost the tribimaximal mixing. The size of the extra dimension has a connection to the possible mass spectrum; a small (large) volume corresponds to the normal (inverted) mass hierarchy.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Quarks in supersymmetry with gauge coupling unification

I investigate the phenomenology of supersymmetric models with extra vectorlike supermultiplets that couple to the standard model gauge fields and transform as the fundamental representation of a new confining non-Abelian gauge interaction. If perturbative gauge coupling unification is to be maintained, the new group can be SU(2), SU(3), or SO(3). The impact on the sparticle mass spectrum is explored, with particular attention to the gaugino mass dominated limit in which the supersymmetric flavor problem is naturally solved. The new confinement length scale is astronomical for SO(3), so the new particles are essentially free. For the SU(2) and SU(3) cases, the new vectorlike fermions are quirks; pair production at colliders yields quirk-antiquirk states bound by stable flux tubes that are microscopic but long compared to the new confinement scale. I study the reach of the Tevatron and LHC for the optimistic case that in a significant fraction of events the quirk-antiquirk bound state will lose most of its energy before annihilating as quirkonium.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Leptogenesis origin of Dirac gaugino dark matter

The Dirac nature of the gauginos (and also the Higgsinos) can be realized in R-symmetric supersymmetry models. In this class of models, the Dirac bino (or wino) with a small mixture of the Dirac Higgsinos is a good dark matter candidate. When the seesaw mechanism with Higgs triplet superfields is implemented to account for the neutrino masses and mixing, the leptogenesis driven by the heavy triplet decay is shown to produce not only the matter-antimatter asymmetry, but also the asymmetric relic density of the Dirac gaugino dark matter. The dark matter mass turns out to be controlled by the Yukawa couplings of the heavy Higgs triplets, and it can be naturally at the weak scale for a mild hierarchy of the Yukawa couplings.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Phenomenological constraints on minimally coupled exotic lepton triplets

By introducing a set of new triplet leptons (with nonzero hypercharge) that can Yukawa couple to their standard model counterparts, new sources of tree-level flavor changing currents are induced via mixing. In this work, we study some of the consequences of such new contributions on processes such as the leptonic decays of gauge bosons, l{yields}3l{sup '} and l{yields}l{sup '{gamma}}, which violate lepton flavor, and {mu}-e conversion in atomic nuclei. Constraints are then placed on the parameters associated with the exotic triplets by invoking the current low-energy experimental data. Moreover, the new physics contribution to the lepton anomalous magnetic moments is calculated.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Supersymmetric three family chiral SU(6) grand unification model from F-theory

We obtain a supersymmetric three family chiral SU(6) grand unification model with the global family symmetry SU(3){sub family} from the use of F-theory. This model has nice features, for instance, all the fermion masses are reasonably generated and result in only one pair of Higgs doublets, giving the doublet-triplet splitting from the family symmetry SU(3){sub family}. The proton hexality is also realized toward the proton stability problem. The model also has a room to fit the three gauge couplings using the F-theory flux idea and we obtain the upper bound of proton lifetime in the 10{sup 36-37} yr region.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Higgs triplets at like-sign linear colliders and neutrino mixing

We study the phenomenology of the type-II seesaw model at a linear e{sup -}e{sup -} collider. We show that the process e{sup -}e{sup -}{yields}{alpha}{sup -}{beta}{sup -} ({alpha}, {beta}=e, {mu}, {tau} being charged leptons) mediated by a doubly charged scalar is very sensitive to the neutrino parameters, in particular, the absolute neutrino mass scale and the Majorana CP-violating phases. We identify the regions in parameter space in which appreciable collider signatures in the channel with two like-sign muons in the final state are possible. This includes Higgs triplet masses beyond the reach of the LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Dark matter in inert triplet models

We study the inert triplet models, in which the standard model is extended to have a new SU(2){sub L} triplet scalar (Y=0 or 2) with an Z{sub 2} symmetry. We show that the neutral component of the triplet can be a good dark matter candidate. In particular, for the hypercharge Y=0 triplet model, the WMAP data favors the region where the dark matter mass is around 5.5 TeV, which is also consistent with the direct detection experiments. In contrast, for the Y=2 model, although dark matter with its mass around 2.8 TeV is allowed by WMAP, it is excluded by the direct detection experiments because the spin-independent cross section is enhanced by the Z-mediated tree-level scattering process.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Testing Higgs models via the H{sup {+-}}W{sup {-+}}Z vertex by a recoil method at the International Linear Collider

In general, charged Higgs bosons H{sup {+-}} appear in nonminimal Higgs models. The H{sup {+-}}W{sup {-+}}Z vertex is known to be related to the violation of the global symmetry (custodial symmetry) in the Higgs sector. Its magnitude strongly depends on the structure of the exotic Higgs models which contain higher isospin SU(2){sub L} representations such as triplet Higgs bosons. We study the possibility of measuring the H{sup {+-}}W{sup {-+}}Z vertex via single charged Higgs boson production associated with the W{sup {+-}} boson at the International Linear Collider (ILC) by using the recoil method. The feasibility of the signal e{sup +}e{sup -}{yields}H{sup {+-}}W{sup {-+}}{yields}l{nu}jj is analyzed assuming the polarized electron and positron beams and the expected detector performance for the resolution of the two-jet system at the ILC. The background events can be reduced to a considerable extent by imposing the kinematic cuts even if we take into account the initial state radiation. For a relatively light charged Higgs boson whose mass m{sub H}{sup {+-}} is in the region of 120-130 GeV <m{sub H}{sup {+-}}<m{sub W}+m{sub Z}, the H{sup {+-}}W{sup {-+}}Z vertex would be precisely testable especially when the decay of H{sup {+-}} is lepton specific. The exoticness of the extended Higgs sector can be explored by using combined information for this vertex and the rho parameter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Metastable dark matter mechanisms for INTEGRAL 511 keV {gamma} rays and DAMA/CoGeNT events

We explore dark matter mechanisms that can simultaneously explain the galactic 511 keV gamma rays observed by INTEGRAL/SPI, the DAMA/LIBRA annual modulation, and the excess of low-recoil dark matter candidates observed by CoGeNT. It requires three nearly degenerate states of dark matter in the 4-7 GeV mass range, with splittings, respectively, of order MeV and a few keV. The top two states have the small mass gap and transitions between them, either exothermic or endothermic, and can account for direct detections. Decays from one of the top states to the ground state produce low-energy positrons in the Galaxy whose associated 511 keV gamma rays are seen by INTEGRAL. This decay can happen spontaneously, if the excited state is metastable (longer lived than the age of the Universe), or it can be triggered by inelastic scattering of the metastable states into the shorter-lived ones. We focus on a simple model where the dark matter is a triplet of an SU(2) hidden sector gauge symmetry, broken at the scale of a few GeV, giving masses of order < or approx. 1 GeV to the dark gauge bosons, which mix kinetically with the standard model hypercharge. The purely decaying scenario can give the observed angular dependence of the 511 keV signal with no positron diffusion, while the inelastic scattering mechanism requires transport of the positrons over distances {approx}1 kpc before annihilating. We note that an x-ray line of several keV in energy, due to single-photon decays involving the top dark matter states, could provide an additional component to the diffuse x-ray background. The model is testable by proposed low-energy fixed-target experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Fermiophobia in a Higgs triplet model

A fermiophobic Higgs boson can arise in models with an extended Higgs sector, such as models with scalars in an isospin triplet representation. In a specific model with a scalar triplet and spontaneous violation of lepton number induced by a scalar singlet field, we show that fermiophobia is not a fine-tuned situation, unlike in two higgs doublet models. We study distinctive signals of fermiophobia which can be probed at the LHC. For the case of a small Higgs mass, a characteristic signal would be a moderate B(H{yields}{gamma}{gamma}) accompanied by a large B(H{yields}JJ) (where J is a Majoron), the latter being an invisible decay. For the case of a large Higgs mass there is the possibility of dominant H{yields}ZZ, WW and suppressed H{yields}JJ decay modes. In this situation, B(H{yields}ZZ) is larger than B(H{yields}WW), which differs from the SM prediction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Supersymmetric left-right models with gauge coupling unification and fermion mass universality

We explore the unification of gauge couplings and fermion masses in two different types of supersymmetric left-right models, one with Higgs triplets and the other with both Higgs triplets as well as bitriplets. The minimal versions of these models do not give rise to the desired unification and some extra fields have to be added. After such a modification, it is possible in one model to get gauged B-L symmetry to be unbroken down to the TeV scale. We also identify the parameter space at the electroweak scale which gives rise to fermion mass unification at a high scale M{sub G}. The Type I seesaw emerges as the natural explanation of the small neutrino masses in both the models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Improvement via hypercubic smearing in triplet and sextet QCD

We study nonperturbative improvement in SU(3) lattice gauge theory coupled to fermions in the fundamental and two-index symmetric representations. Our lattice action is defined with hypercubic smeared links incorporated into the Wilson-clover fermion kernel. Using standard Schroedinger-functional techniques, we estimate the clover coefficient c{sub SW} and find that discretization errors are much smaller than in thin-link theories.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Higgs quadruplet for the type III seesaw model and implications for {mu}{yields}e{gamma} and {mu}-e conversion

In the type III seesaw model, the heavy neutrinos are contained in leptonic triplet representations. The Yukawa couplings of the triplet fermion and the left-handed neutrinos with the doublet Higgs field produce the Dirac mass terms. Together with the Majorana masses for the leptonic triplets, the light neutrinos obtain nonzero seesaw masses. We point out that it is also possible to have a quadruplet Higgs field to produce the Dirac mass terms to facilitate the seesaw mechanism. The vacuum expectation value of the quadruplet Higgs is constrained to be small by electroweak precision data. Therefore, the Yukawa couplings of a quadruplet can be much larger than those for a doublet. We also find that unlike the usual type III seesaw model where at least two copies of leptonic triplets are needed, with both doublet and quadruplet Higgs representations, just one leptonic triplet is possible to have a phenomenologically acceptable model because light neutrino masses can receive sizable contributions at both tree and one-loop levels. Large Yukawa couplings of the quadruplet can induce observable effects for lepton flavor violating processes {mu}{yields}e{gamma} and {mu}-e conversion. Implications of the recent {mu}{yields}e{gamma} limit from MEG and the limit on {mu}-e conversion on Au are also given. Some interesting collider signatures for the doubly charged Higgs boson in the quadruplet are discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗