Scalar SU Research Articles

Consequences of triplet seesaw for leptogenesis

We present the various leptogenesis scenarios which may occur if, in addition to the ordinary heavy right-handed neutrinos, there exists a heavy scalar SU(2)L triplet coupled to leptons. We show that the contributions of the right-handed neutrinos and the triplet to the lepton asymmetry are proportional to their respective contributions to the neutrino mass matrix. A consequence of the triplet contribution to the lepton asymmetry is that there is no more upper bound on the neutrino masses from leptogenesis due to the fact that the neutrino mass constraints do not necessarily induce asymmetry washout effects. We also show how such a triplet leptogenesis mechanism may emerge naturally in the framework of the left–right symmetric theories, such as Pati–Salam or SO(10).

A non-singular infra-red flow from D=5 gauged supergravity

We discuss domain wall solutions of 5-dimensional supergravity corresponding to a cosine-superpotential, which is derived by a gauging of the two Abelian isometries of the scalar coset SU(2,1)/ U(2). We argue that this potential can be obtained from M-theory compactification in the presence of G-fluxes and an M5-brane instanton gas. If we decouple the volume scalar of the internal space, the superpotential allows for two extrema, which are either ultra-violet or infra-red attractive. Asymptotically we approach therefore either the boundary or the Killing horizon of an anti-deSitter space or flat spacetime for a vanishing cosmological constant. If the volume scalar does not decouple, we obtain a run-away potential corresponding to dilatonic domain walls, which always run towards a vanishing cosmological constant.

Euclidean Field Theory and Singular Classical Field Configurations

Euclidean field theory on a three-dimensional sphere is suggested for the study of high energy multiparticle production. The singular classical field configurations are found in scalar φ4 and SU(2) gauge theories, and the cross-section of 2→n is calculated. It is shown that the cross-section has a maximum at an energy comparable with that of the sphaleron mass.

Scale of SU(2) R symmetry breaking and leptogenesis

Models of leptogenesis often invoke the out-of-equilibrium decays of heavy right-handed neutrinos in order to create a baryon asymmetry of the universe through the electroweak phase transition. Their presumed existence argues strongly for the presence of an SU(2) R gauge symmetry. We study the equilibrating effects of the resulting additional right-handed interactions and find that successful leptogenesis requires that m N ≳10 16 GeV if m N > m W R , and m W R ≳2×10 5 GeV(m N/10 2 GeV) 3/4 if m N < m W R , where m N is the mass of the lightest right-handed neutrino. A better bound m W R ≳3×10 6 GeV(m N/10 2 GeV) 2/3 is obtained if leptogenesis occurs at T> m W R . We show also that the m N > m W R option is excluded in a supersymmetric theory with gravitinos.

Scaling in SU(3) theory with a MCRG improved lattice action

We test various improved gauge actions which are made of linear combinations of Wilson loops. We observe the restoration of rotational symmetry in the static interquark potential already on coarse lattices as small as 6 312. Furthermore, we study scaling and asymptotic scaling of the string tension with a MCRG-improved action on 12 324 lattices. Preliminary results show that scaling sets in at a 0.3 fm.

Scaling in SU(3) pure gauge theory with a renormalization-group-improved action

We study the scaling properties of the static quark potential and the ratio of the critical temperature ${T}_{c}$ to the square root of the string tension $\ensuremath{\sigma}$ in the SU(3) pure gauge theory using a renormalization-group-improved action. We first determine the critical coupling ${\ensuremath{\beta}}_{c}$ on lattices with a temporal extension ${N}_{t}=3$, 4, and 6, and then calculate the static quark potential at the critical couplings on lattices at zero temperature. We note that the static quark potentials obtained are rotationally invariant with errors of at most 1--2 % in all three cases, and that the potential $V(R)$ in physical units scales in the whole region of $R$ investigated. The values of ${T}_{c}/\sqrt{\ensuremath{\sigma}}$ for the three cases in the infinite volume limit are identical within errors. We estimate the value in the continuum limit to be ${T}_{c}/\sqrt{\ensuremath{\sigma}}=0.656(4)$, which is slightly larger than the value in the continuum limit from the one-plaquette action, 0.629(3).

Reduction of the finite grand unification theory to the minimal supersymmetric standard model

The recently proposed mechanism for reducing the finite SU(5) grand unification theory (GUT) to the minimal supersymmetric standard model (MSSM) is reanalyzed and simplified. For the scalar SU(2)×U(1) invariant Higgs doublet potential that results from SU(5) symmetry breaking to have no dangerous directions, a restriction on the parameters of the unified theory should be imposed. At the same time, this restriction guarantees that the scalar Higgs doublet potential has a minimum at zero at the GUT scale, and the low-energy theory appears to be exactly the MSSM.

Scaling in SU(3) Pure Gauge Theory with a Renormalization Group Improved Action

Scaling in SU(3) Pure Gauge Theory with a Renormalization Group Improved Action

Dual versions of extended supergravities

Recently, using the model of N = 2 supergravity — vector multiplets interaction with the scalar field geometry SU(1,m) SU(m) ⊗ U(1) as an example, we have shown that even when the scalar field geometry is fixed, one can have a whole family of Lagrangians, which differ by vector field duality transformation. In this paper we carry out the construction of such families for the case of N = 3 and N = 4 supergravities, the scalar field geometry being SU(3,m) SU(3) ⊗ SU(m) ⊗ U(1) and SU(1,1) U(1) ⊗ O(6,m) O(6) ⊗ O(m) , correspondingly. Moreover, it turns out that these families contain, as a partial case, the models describing the interaction of an arbitrary number of vector multiplets with our hidden sectors, admitting spontaneous supersymmetry breaking without a cosmological term.

Helicity flip of a neutrino in vℓ scattering in the extended electroweak model with an SU L(2) charged singlet

In the electroweak model with a charged scalar SU L(2) singlet we have calculated the cross section for scattering of an anti-neutrino by leptons with helicity flip ( v ̃ +ℓ→ v ̃ −ℓ ), which considerably (by more than five orders of magnitude under the conditions described below) exceeds the cross section for v ̃ ℓ scattering in an electromagnetic channel, which is due to the existence of a vacuum magnetic moment of the neutrino. New cosmological restrictions on the constants of the model used, ƒ ab and g ab , have been obtained.

String corrections and asymptotic scaling in SU(2) and SU(3) lattice gauge theories

We give a set of recipes to extract reliable values of the string tension from Montecarlo data on Wilson loops. These recipes have a natural “string” interpretation: they take into account the zero point (vacuum) energy and the self-interaction of the string which in the confining regime bounds together quarks and antiquarks. In particular we apply our method to SU(2) and SU(3) gauge models in 4 dimensions and obtain values of the string tension which fulfil asymptotic scaling in a wide range of β.

Failure of perturbative scaling in SU(3) lattice gauge theory

The Asymptotic Freedom (AF) prediction for the energy density of the pure SU(3) Yang-Mills theory in a constant abelian chromomagnetic field is clearly seen to be inconsistent with a lattice calculation. This failure of AF fully confirms previous results obtained for SU(2), both analytically and by lattice methods. In view of this important confirmation, we conclude that the generally accepted picture of QCD can not be maintained in its present form.

Unitarity constraints on CP nonconservation in Higgs-boson exchange.

Bounds are derived for the dimensionless factors that enter in the violation of {ital CP} invariance in Higgs-boson exchange. In particular, for the class of theories with two scalar SU(2){times}U(1) doublets (plus any other scalars whose expectation values do not break SU(2){times}U(1)), the magnitude of the parameter Im {ital Z}{sub 2}, which appears in the dominant neutral-Higgs-boson-exchange contribution to the neutron electric dipole moment, is bounded by 1/2({ital r}{sup 2}+{ital r}{sup 4}){sup 1/2}, where {ital r} is a ratio of the magnitudes of scalar vacuum expectation values. It is shown that this bound can actually be reached in realistic models.

Experimental tests of separating electroweak and flavor symmetry breaking

We introduce a model in which a scalar doublet breaks SU(2) × U(1) but not the fermions' flavor symmetries. The latter are broken in heavy Dirac SU(2)-singlet fermions. We discuss direct searches for those fermions and their effects on Z-pole physics.

Separating electroweak symmetry breaking from flavor physics in an almost-standard model

We introduce a model in which a scalar doublet breaks SU(2) × U(1) and helps generate the masses of ordinary fermions but is not responsible for flavor symmetry breaking. The latter is accomplished by heavy Dirac SU(2)-singlet fermions. The phenomenology of the model including effects on universality, K 0 K 0 mixing and the decay K → πν ν is discussed in detail. We also analyze the best means of searching for the heavy singlet fermions including direct production and effects at the Z-boson pole.

Phenomenology of a technicolor model with heavy scalar doublet

Rather than having a light scalar both break SU(2) × U(1) and give mass to the fermions, as in the standard model, it is possible to use technicolor to do the first while a heavy (∼ 10 TeV) scalar does the second. The impact of such a heavy scalar on FCNC in the Kaon and B-meson systems is explored here.

Universality and scaling in SU(2) lattice gauge theory

We calculate the lowest glueball masses and the string tension for both Manton's action and for Symanzik's tree-level improved action. We do so on large lattices and for small lattice spacings using techniques recently employed in an extensive investigation of the Wilson plaquette action. Comparing all these results we find that the ratios of the lightest masses are universal to a high degree of accuracy. In particular, we confirm that on large volumes the tensor glueball is heavier than the scalar glueball: m[2 +]⋍1.5 m[0 +] . We repeat these calculations for larger lattice spacings and find that the string tension follows 2-loop perturbation theory more closely in the case of these alternative actions than in the case of the standard plaquette action. Our attempt to repeat the analysis with Wilson's block-spin improved action foundered on the strong breakdown of positivity apparent in the calculated correlation functions. In all cases which we were able to study the observed violations of scaling are in the same direction. This suggests that the causes of the scaling violations observed with Wilson's plaquette action are “semi-universal”. It also weakens the implication of the observed universality for the question of how close we are to the continuum limit.

Natural seesaw mechanism, eV-keV-MeV-type neutrino spectrum, and cosmology.

We show that in left-right-symmetric models one can have ${\mathit{m}}_{\mathit{v}\mathit{e}}$:${\mathit{m}}_{\mathit{v}\mathrm{\ensuremath{\mu}}}$:${\mathit{m}}_{\mathit{v}\mathrm{\ensuremath{\tau}}}$\ensuremath{\simeq}eV:KeV:MeV without any fine-tuning of parameters. The ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ and ${\ensuremath{\nu}}_{\ensuremath{\tau}}$ decay via Majoron emission with lifetimes short enough to avoid cosmological constraints. The key ingredient of the model is the breaking of D parity, present in SO(10), at a scale much higher than the scale of SU(2${)}_{R}$ breaking. Using the Fritzsch ansatz for up-quark mass matrices and a diagonal form for the heavy neutrino masses, we predict 10 TeV, and \ensuremath{\ge}0.2 eV.

The glueball spectrum and scaling in SU(3) lattice gauge theory

We calculate glueball masses and the string tension on lattices as large as 20 4 and at couplings as small as β= 6 g 2 =6.2 . To be able to do so we construct wave-functionals that maintain a good overlap with the long-distance physics as the lattice spacing is made small. Our calculations strongly indicate that the lightest glueball is the 0 ++ and that the next highest levels are a nearly degenerate 2 ++ and 0 −+ at roughly 1.6 m[0 ++]. In addition there is a 1 +− just below 2 m[0 ++]. The mass of the scalar is about 3.5 times the square root of the string tension. We find that this ratio is consistent with being independent of β for β⩾5.9 (in contrast to its strong variation at lower β) and that this appears tobe so at a statistically significant level. The ratio of the 2 ++ and 0 ++ glueball masses is also consistent with being independent of β.

Departures from scaling in SU(2) lattice gauge theory

High statistics Monte Carlo Data in SU(2) lattice gauge theory are presented. At β = 2.6 and β = 2.7 large deviations from scaling are observed for Creutz ratios, when 12 4 and 24 4 lattice data are compared. There is a trend towards a restauration of asymptotic scaling with increasing β, which vanishes if at the higher value of β larger loops are considered than at lower β. The static qq̄-potential and an upper limit for the string tension are given.