Discovering mirror particles at the Large Hadron Collider and the implied cold universe

The Mirror Matter or Exact Parity Model sees every standard particle, including the physical neutral Higgs boson, paired with a parity partner. The unbroken parity symmetry forces the mass eigenstate Higgs bosons to be maximal mixtures of the ordinary and mirror Higgs bosons. Each of these mass eigenstates will therefore decay 50% of the time into invisible mirror particles, providing a clear and interesting signature for the Large Hadron Collider (LHC) which could thus establish the existence of the mirror world. However, for this effect to be observable the mass difference between the two eigenstates must be sufficiently large. In this paper, we study cosmological constraints from Big Bang Nucleosynthesis on the mass difference parameter. We find that the temperature of the radiation dominated (RD) phase of the universe should never have exceeded a few 10's of GeV if the mass difference is to be observable at the LHC. Chaotic inflation with very inefficient reheating provides an example of how such a cosmology could arise. We conclude that the LHC could thus discover the mirror world and simultaneously establish an upper bound on the temperature of the RD phase of the universe.Comment: 8pages including 1 figure, RevTeX; minor changes and added references; this version accepted by Phys Lett

Maximal νe→νs\nu_e \to \nu_s solution to the solar neutrino problem: just-so, MSW or energy independent?

We examine the maximal $\nu_e \to \nu_s$ solution to the solar neutrino problem. This solution can be motivated by the exact parity model and other theories. The $\nu_e$ survival probability exhibits one of three qualitatively different behaviours depending on the value of $\Delta m^2$, viz. approximately energy independent, just-so or MSW. By the last of these we mean an enhanced night-time event rate due to regeneration in the Earth. We study all of these possibilities in the context of the recent SuperKamiokande data.Comment: minor changes to text and fig.

Comment on ``Neutrino oscillations in the early universe: how can large lepton asymmetry be generated?"

We comment on the recent paper by A. D. Dolgov, S. H. Hansen, S. Pastor and D. V. Semikoz (DHPS) [Astropart. Phys. {\bf 14}, 79 (2000)] on the generation of neutrino asymmetries from active-sterile neutrino oscillations. We demonstrate that the approximate asymmetry evolution equation obtained therein is an expansion, up to a minor discrepancy, of the well-established static approximation equation, valid only when the supposedly new higher order correction term is small. In the regime where this so-called ``back-reaction'' term is large and artificially terminates the asymmetry growth, their evolution equation ceases to be a faithful approximation to the Quantum Kinetic Equations (QKEs) simply because pure Mikheyev-Smirnov-Wolfenstein (MSW) transitions have been neglected. At low temperatures the MSW effect is the dominant asymmetry amplifier. Neither the static nor the DHPS approach contains this important physics. Therefore we conclude that the DHPS results have sufficient veracity at the onset of explosive asymmetry generation, but are invalid in the ensuing low temperature epoch where MSW conversions are able to enhance the asymmetry to values of order $0.2 - 0.37$. DHPS do claim to find a significant final asymmetry for very large $\delta m^2$ values. However, for this regime the effective potential they employed is not valid.Comment: RevTeX, 32 pages, including 4 embedded figures; this version to appear in Astropart.Phy

The neutrino puzzle in the light of SNO

SNO's neutral current measurement has added a new piece to the emerging neutrino physics puzzle. Putting together the presently available experimental information, an essentially unique picture emerges: The solar neutrino anomaly is explained by nu_e --> nu_tau oscillations, the atmospheric neutrino anomaly is explained by nu_{mu} --> nu_s and the LSND data are explained by nu_e --> nu_{mu}. This scheme will be tested by future experiments: MiniBooNE will test the oscillation explanation of the LSND anomaly, while the long baseline experiments will discriminate between the nu_{mu} --> nu_s and nu_{mu} --> nu_{tau} possibilities for resolving the atmospheric anomaly (confirming or disconfirming the Super-Kamiokande result that the latter is favoured over the former).Comment: about 4 pages, expanded discussio

Effects for atmospheric neutrino experiments from electron neutrino oscillations

The minimal interpretation of the atmospheric neutrino data suggests that the muon neutrino oscillates into another species with a mixing angle close to the maximal $\pi/4$. In the Exact Parity Symmetric Model, both the muon and electron neutrinos are expected to be maximally mixed with essentially sterile partners ($\nu'_{\mu}$ and $\nu'_e$ respectively). We examine the impact of maximal $\nu_e - \nu'_e$ oscillations on the atmospheric neutrino experiments. We estimate that maximal $\nu_e - \nu'_e$ oscillations will have effects on atmospheric neutrino data for $|\delta m^2 (\nu_e - \nu_e')| > 7 \times 10^{-5} eV^2$. For $\delta m^2$ in this range, a slight but distinctive rise in the ratio of muon-like to electron-like events is predicted for the low-energy sample. Furthermore, the ratio of low-energy electron-like events with zenith angles less than $90\deg$ to those with zenith angles greater than $90\deg$ should be greater than 1.Comment: 11 pages, LaTeX, no figure

A mirror world explanation for the Pioneer spacecraft anomalies?

We show that the anomalous acceleration of the Pioneer 10/11 spacecraft can be explained if there is some mirror gas or mirror dust in our solar system.Comment: Latex, 7 pages, accepted in Phys. Lett.

Electroweak Phase Transitions in left-right symmetric models

We study the finite-temperature effective potential of minimal left-right symmetric models containing a bidoublet and two triplets in the scalar sector. We perform a numerical analysis of the parameter space compatible with the requirement that baryon asymmetry is not washed out by sphaleron processes after the electroweak phase transition. We find that the spectrum of scalar particles for these acceptable cases is consistent with present experimental bounds.Comment: 20 pages, 5 figures (included), some comments added, typos corrected and new references included. Final version to appear in PR

Composite quarks and leptons in higher space-time dimensions

A new approach towards the composite structure of quarks and leptons in the context of the higher dimensional unified theories is proposed. Owing to the certain strong dynamics, much like an ordinary QCD, every possible vectorlike multiplets of composites appear in higher dimensional bulk space-time, however, through a proper Sherk-Schwarz compactification only chiral set of composite quarks and leptons survive as the massless states in four dimensions. In this scenario restrictions related with the 't Hooft's anomaly matching condition are turned out to be avoided and, as a result, the composite models look rather simple and economic. We demonstrate our approach by an explicit construction of model of preons and their composites unified in the supersymmetric SU(5) GUT in five space-time dimensions. The model predicts exactly three families of the composite quarks and leptons being the triplets of the chiral horizontal symmetry SU(3)_h which automatically appears in the composite spectrum when going to ordinary four dimensions.Comment: 13 pages, tcilatex, no figures, v2 - misprints correcte