arXiv subjects

Jukka Maalampi

Publications and source records attributed to Jukka Maalampi.

33 records · Page 2Linked to original sources

arXiv2002

Single production of doubly charged Higgs bosons at hadron colliders

We reconsider the single production of the doubly charged Higgs bosons Delta_R^{++} and Delta_L^{++} at the LHC and TEVATRON in the framework of the left-right symmetric model and the Higgs triplet model. We show that in the left-right symmetric model the production of Delta_R^{++} by Drell-Yan process via W_R exchange may give the dominant contribution. The same channel for the production of Delta_L^{++} in the Higgs triplet model is insignificant.

hep-ph↗

arXiv2001

Revisiting pseudo-Dirac neutrinos

We study the pseudo-Dirac mixing of left and right-handed neutrinos in the case where the Majorana masses M_L and M_R are small when compared with the Dirac mass, M_D. The light Majorana masses could be generated by a non-renormalizable operator reflecting effects of new physics at some high energy scale. In this context, we obtain a simple model independent closed bound for M_D. A phenomenologically consistent scenario is achieved with M_L,M_R ~ 10^{-7} eV and M_D ~ 10^{-5}-10^{-4} eV. This precludes the possibility of positive mass searches in the planned future experiments like GENIUS or in tritium decay experiments. If on the other hand, GENIUS does observe a positive signal for a Majorana mass \geq 10^{-3} eV, then with very little fine tuning of neutrino parameters, the scale of new physics could be in the TeV range, but pseudo-Dirac scenario in that case is excluded. We briefly discuss the constraints from cosmology when a fraction of the dark matter is composed of nearly degenerate neutrinos.

hep-ph↗

arXiv2000

Searching Scalar Resonances with Ultra-high Energy Neutrinos

We study the prospects of detecting signals of a resonant scattering of high-energy cosmic neutrinos on electrons in the atmosphere. Such a process is possible through an s-channel exchange of a isotriplet scalar particle predicted by some particle physics theories. We estimate the event rates for a reference detector setup with plausible assumptions on the interaction strengths and energy resolutions. We find as the most promising process the resonance production of tau neutrinos whose signature would be a "quiet" (in contrast with a hadronic "bang") production of the tau lepton followed by a more noisy decay in downstream.

hep-ph↗

arXiv2000

Neutrinoless double beta decay in four-neutrino models

The most stringent constraint on the so-called effective electron neutrino mass from the present neutrinoless double beta decay experiments is |M_{ee}| < 0.2 eV, while the planned next generation experiment GENIUS is anticipated to reach a considerably more stringent limit |M_{ee}|< 0.001 eV. We investigate the constraints these bounds set on the neutrino masses and mixings of neutrinos in four-neutrino models where there exists a sterile neutrino along with the three ordinary neutrinos. We find that the GENIUS experiment would be sensitive to the electron neutrino masses down to the limit m_{ν_e}\lsim 0.024 eV in such a scenario.

hep-ph↗

arXiv2000

Neutrino mixing scenarios and AGN

Active galactic nuclei (AGN) have been suggested to be sources of very high energy neutrinos. We consider the possibility of using AGN neutrinos to test neutrino mixings. From the atmospheric, solar and laboratory data on neutrino oscillations we derive the flavour composition of the AGN neutrino flux in different neutrino mixing schemes. We show that most of the schemes considered can be distinguished from each other and the existence of a sterile neutrino can be specially tested. AGN neutrinos can also be used to test those four-neutrino scenarios where solar neutrinos oscillate into an arbitrary mixture of $ν_s$ and $ν_τ$.

hep-ph↗

arXiv1999

Search for CP Violation at a Neutrino Factory in a Four-Neutrino Model

The CP violation effects in long baseline neutrino oscillations are studied in the framework of a four-neutrino model (three active neutrinos and one sterile neutrino). It is assumed that neutrino masses are devided into two nearly degenerate pairs, as indicated by the oscillation data. Approximative analytic expressions are derived for the probability differences $ΔP_{\a\b} \equiv P(ν_α\to ν_β)- P(\barν_α\to \barν_β)$ taking into account the CP violation effect of the Earth's crust. The matter effect is found to be small compared with the genuine CP violation term, in contrast with the three-neutrino model.

hep-ph↗

arXiv1999

Production of four jets in LR model

We consider the reaction ee -> q,q,qbar,qbar as a test of lepton number non-conservation in the framework of the left-right-symmetric electroweak model. The main contributions to this process are due to Majorana neutrino exchange in t-channel and doubly charged Higgs (Delta(--)) exchange in s-channel with a pair of right-handed weak bosons (WR) as intermediate state. We show that in a linear ee collider with the collision energy of 1 TeV (1.5 TeV) the cross section of this process is 0.01 fb (1 fb), and it will, for the anticipated luminosity of 10**35 cm**(-2)s**(-1), be detectable below the WR threshold. We study the sensitivity of the reaction on the masses of the heavy neutrino, WR and Delta(--).

hep-ph↗

arXiv1999

Testing lepton number violation with the reaction e,e -> mu, nu, q, q

We investigate the reaction e,e->mu, nu, q, q as a possible place to test the lepton number violating interactions of singly charged scalars (Delta(L)) belonging to a SU(2)L triplet. The existence of such scalars is predicted by some majoron models, as well as by the left-right symmetric extension of the Standard Model. We show that this reaction may be observed in ee collision well below the threshold of (Delta(L)). For the colliding energy E=500 GeV the mass of the singly charged Higgs triplet may be excluded up to 2 TeV and even more, depending on values of the appropriate Yukawa couplings.

hep-ph↗

arXiv1998

Testing neutrino magnetic moments with AGNs

We propose to test the magnetic transition moments of Majorana neutrinos by comparing the fluxes of different flavours of neutrinos coming from active galactic nuclei (AGN). We show that, with reasonable assumptions about the magnetic field of the AGN, it is possible to obtain limits on $ν_τν_{e}$ and $ν_τν_μ$ transition moments which are three to five orders of magnitude better than the laboratory limits. We also point out that with certain parameter values the ratio $ν_τ/ν_{e,μ}$, when measured from different sources, is expected to vary from zero to values somewhat higher than one, providing an unambigious signal of a magnetic transition within the AGN which cannot be explained by neutrino oscillations.

hep-ph↗

arXiv1996

Cosmological abundances of right-handed neutrinos

We study the equilibration of the right-helicity states of light Dirac neutrinos in the early universe by solving the momentum dependent Boltzmann equations numerically. We show that the main effect is due to electroweak gauge boson poles, which enhance thermalization rates by some three orders of magnitude. The right-helicity states of tau neutrinos will be brought in equilibrium independently of their initial distribution at a temperature above the poles if the tau neutrino mass is larger than about 10 keV.

hep-ph↗

arXiv1995

Damping rate of neutrinos in the singlet Majoron model

The damping rate and free path of neutrinos in the singlet Majoron model have been calculated including both finite temperature and symmetry breaking effects. The behaviour of right- and left-handed fermions are found inherently different. While the damping rates of the left-handed leptons are essentially model independent, e.g. directly applicable to the Standard Model, for the right-handed particles the rates are crucially sensitive to parameters of the scalar sector. In general, the damping rates are fairly large. The possibility of the right-handed neutrinos to penetrate deep into the broken phase in the electroweak phase transition still remains, however, for some parts of parameter space.

hep-ph↗

arXiv1995

Neutrino conversions in hot plasma

We discuss the excitation of sterile neutrinos in the early universe using general quantum kinetic equations, which also incorporate a possible primordial magnetic field $B$. We find a new contribution to the excitation propability, which has its origin in the shrinkage of the spin vector. In the absence of $B$ nucleosynthesis implies the constraint $\mid Δm^2\mid\sin^22θ_0\lsim 1.6\times 10^{-6}~{\rm eV}^2$ which is more restrictive than previous estimates. We also present examples of possible stringent limits for $B\ne 0$.

hep-ph↗

arXiv1994

The Higgs sector of a supersymmetric left-right model

We study the symmetry breaking sector of a supersymmetric left-right model based on the gauge group $SU(2)_L\times SU(2)_R\times U(1)_{B-L}$. The explicit mass matrices of neutral, singly charged and doubly charged scalars are constructed. In the minimum the $R$-parity is found to be spontaneously broken. An experimentally interesting feature of the model is that one of the doubly charged scalars is possibly light enough to be seen in the next linear collider.

hep-ph↗

arXiv1994

Vector boson pair production in e-e- collisions with polarized beams

The $W$-boson pair production in $e^-e^-$ collisions with polarized beams is investigated. The helicity amplitudes are derived for general couplings and the conditions for a good high-energy behaviour of the cross-section are given. The results are applied to the heavy vector boson production in the context of the left-right symmetric model. The Ward identities and the equivalence theorem are also discussed.

hep-ph↗

arXiv1993

Signatures of left-right symmetry at high energies

We discuss various experimental tests of the left-right symmetric model possible to perform in the next generation linear colliders. We consider processes which provide sensitive probes of the basic ingredients of the model: right-handed gauge bosons, right-handed Majorana neutrinos, lepton number violating interactions and triplet Higgs scalars. A supersymmetric version of the left-right model is also studied and some distinctive experimental tests for it is proposed. One of the main messages of this talk is to emphasize the usefulness of the collision modes $e^-e^-$, $e^-γ$ and $γγ$ for the tests of the left-right symmetric model.

hep-ph↗