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R. Foot

Publications and source records attributed to R. Foot.

At least 91 records · Page 5Linked to original sources
arXiv2001

Do "isolated" planetary mass objects orbit mirror stars?

We propose that the ``isolated'' planetary mass objects observed by Zapatero Osorio et al in the $σ$ Orionis cluster might actually be in orbit around invisible stellar mass companions such as mirror stars. Mirror matter is expected to exist if parity is an unbroken symmetry of nature. Future observations can test this idea by looking for a periodic Doppler shift in the radiation emitted by the planets. The fact that the observations show an inverse dependence between the abundance of the these objects and their mass may argue in favour of the mirror matter hypothesis.

astro-ph↗
arXiv2000

Physics of mirror photons

The physics of kinetic mixing between ordinary and mirror photons is discussed. An important role is played by four linear combinations we dub the physical photon, the sterile photon, the physical mirror photon, and the sterile mirror photon. Because of the mass degeneracy between the two gauge bosons, quantum coherence effects are important. The physical photon becomes a certain coherent superposition of the bare ordinary photon and the bare mirror photon. Similarly, the physical mirror photon is another, but {\it not orthogonal}, coherent superposition. We discuss the physics of the interaction between physical mirror photons and ordinary matter. Observational signatures for some hybrid ordinary/mirror binary astrophysical systems are qualitatively discussed. We show that a small amount of ordinary matter at the center of a mirror star may make the mirror star observable. We speculate that the recently reported halo white dwarfs might actually be mirror halo stars.

astro-ph↗
arXiv2000

Active-Sterile neutrino oscillations and BBN+CMBR constraints

We show how active-sterile neutrino oscillations in the early Universe can play an interesting role in explaining the current observations of CMBR anisotropies and light element abundances. We describe different possible phenomenological scenarios in the interpretation of present data and how active-sterile neutrino oscillations can provide a viable theoretical framework.

hep-ph↗
arXiv2000

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 $δm^2$ values. However, for this regime the effective potential they employed is not valid.

hep-ph↗
arXiv2000

Maximal $ν_μ- ν_τ$ oscillations, the see-saw mechanism and the Exact Parity Model

We examine one simple mechanism which leads to approximate maximal $ν_μ- ν_τ$ oscillations in the standard see-saw model. In particular, we show that this scheme could be implemented in the Exact Parity Model (also known as the mirror matter model). Within this framework the solar neutrino problem is solved by maximal $ν_e \to ν'_e$ oscillations (with $ν'_e$ is the essentially sterile mirror partner of $ν_e$) and the LSND evidence for $ν_e \to ν_μ$ oscillations can also be explained.

hep-ph↗
arXiv2000

Unbroken versus broken mirror world: a tale of two vacua

If the Lagrangian of nature respects parity invariance then there are two distinct possibilities: either parity is unbroken by the vacuum or it is spontaneously broken. We examine the two simplest phenomenologically consistent gauge models which have unbroken and spontaneously broken parity symmetries, respectively. These two models have a Lagrangian of the same form, but a different parameter range is chosen in the Higgs potential. They both predict the existence of dark matter and can explain the MACHO events. However, the models predict quite different neutrino physics. Although both have light mirror (effectively sterile) neutrinos, the ordinary-mirror neutrino mixing angles are unobservably tiny in the broken parity case. The minimal broken parity model therefore cannot simultaneously explain the solar, atmospheric and LSND data. By contrast, the unbroken parity version can explain all of the neutrino anomalies. Furthermore, we argue that the unbroken case provides the most natural explanation of the neutrino physics anomalies (irrespective of whether evidence from the LSND experiment is included) because of its characteristic maximal mixing prediction.

hep-ph↗
arXiv2000

Maximal $ν_e$ oscillations, Borexino and smoking guns

We examine the maximal $ν_e --> ν_s$ and $ν_e --> ν_μ,τ$ oscillation solutions to the solar neutrino problem. These solutions lead to roughly a 50% solar flux reduction for the large parameter range $3\times 10^{-10} < δm^2/eV^2 < 10^{-3}$. It is known that the earth regeneration effect may cause a potentially large night-day asymmetry even for maximal neutrino oscillations. We investigate the night-day asymmetry predictions for the forthcoming Borexino measurement of the ^7Be neutrinos for both maximal $ν_e --> ν_s$ and $ν_e --> ν_μ,τ$ oscillations. If $y \times 10^{-8} < δm^2/eV^2 < 4y \times 10^{-5}$ (with y = 0.5 for $ν_e --> ν_s$ case and y = 1 for $ν_e --> ν_μ,τ$ case) then the maximal neutrino oscillations will lead to observable night-day asymmetries in Borexino and/or superKamiokande. With Kamland covering the high mass range, $10^{-5} < δm^2/eV^2 < 10^{-3}$ and Borexino/superK covering the low mass range, $3\times 10^{-10} < δm^2/eV^2 < 5\times 10^{-9}$ ("just so" region), essentially all of the $δm^2$ parameter space will soon be scrutinized.

hep-ph↗
arXiv2000

On the sign of the neutrino asymmetry induced by active-sterile neutrino oscillations in the early Universe

We deal with the problem of the final sign of the neutrino asymmetry generated by active-sterile neutrino oscillations in the Early Universe solving the full momentum dependent quantum kinetic equations. We study the parameter region $10^{-2} \stackrel{<}{\sim} |δm^2|/eV^2\le 10^3$. For a large range of $\sin^2 2θ_0$ values the sign of the neutrino asymmetry is fixed and does not oscillate. For values of mixing parameters in the region $10^{-6}\stackrel{<}{\sim}\sin^{2}2θ_{0}\stackrel{<}{\sim} 3\times 10^{-4} ({\rm eV}^{2}/|δm^{2}|)$, the neutrino asymmetry appears to undergo rapid oscillations during the period where the exponential growth occurs. Our numerical results indicate that the oscillations are able to change the neutrino asymmetry sign. The sensitivity of the solutions and in particular of the final sign of lepton number to small changes in the initial conditions depends whether the number of oscillations is high enough. It is however not possible to conclude whether this effect is induced by the presence of a numerical error or is an intrinsic feature. As the amplitude of the statistical fluctuations is much lower than the numerical error, our numerical analysis cannot demonstrate the possibility of a chaotical generation of lepton domains. In any case this possibility is confined to a special region in the space of mixing parameters and it cannot spoil the compatibility of the $ν_μ\leftrightarrowν_{s}$ solution to the neutrino atmospheric data obtained assuming a small mixing of the $ν_{s}$ with an ${\rm eV}-τ$ neutrino.

hep-ph↗
arXiv1999

Have mirror planets been observed?

Over the last few years, several close orbiting ($\sim 0.05$ AU) large mass planets ($M \sim M_{Jupiter}$) of nearby stars have been discovered. Their existence has been inferred from tiny doppler shifts in the light from the star. We suggest that these planets may be made of mirror matter. We also suggest that some stars such as our sun may have a similar amount of mirror matter which has escaped detection.

astro-ph↗
arXiv1999

Detailed study of BBN implications of neutrino oscillation generated neutrino asymmetries in some four neutrino models

We re-examine the evolution of neutrino asymmetries in several four neutrino models. The first case involves the direct creation of $L_{ν_e}$ by $ν_e \leftrightarrow ν_s$ oscillations. In the second case, we consider the mass hierarchy $m_{ν_τ} \gg m_{ν_μ}, m_{ν_e}, m_{ν_s}$ where $ν_τ\leftrightarrow ν_s$ oscillations generate a large $L_{ν_τ}$ and some of this asymmetry is converted into $L_{ν_e}$ by $ν_τ \leftrightarrow ν_{e}$ oscillations. We estimate the implications for BBN for a range of cosmologically interesting $δm^2$ values. The present paper improves on previous published work by taking into account the finite repopulation rate and the time dependence of the distortions to the neutrino momentum distributions. The treatment of chemical decoupling is also improved.

hep-ph↗
arXiv1999

Maximal $ν_e \to ν_s$ solution to the solar neutrino problem: just-so, MSW or energy independent?

We examine the maximal $ν_e \to ν_s$ solution to the solar neutrino problem. This solution can be motivated by the exact parity model and other theories. The $ν_e$ survival probability exhibits one of three qualitatively different behaviours depending on the value of $Δm^2$, 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.

hep-ph↗
arXiv1999

Implications of mirror neutrinos for early universe cosmology

The Exact Parity Model (EPM) is, in part, a theory of neutrino mass and mixing that can solve the atmospheric, solar and LSND anomalies. The central feature of the neutrino sector is three pairs of maximally mixed ordinary and mirror neutrinos. It has been shown that ordinary-mirror neutrino oscillations can generate large neutrino asymmetries in the epoch of the early universe immediately prior to Big Bang Nucleosynthesis (BBN). The large neutrino asymmetries generically suppress the production of mirror neutrinos, and a sufficiently large $ν_e$ asymmetry can directly affect light element synthesis through nuclear reaction rates. In this paper we present a detailed calculation of neutrino asymmetry evolution driven by the six-flavour EPM neutrino sector, focusing on implications for BBN.

hep-ph↗
arXiv1999

Implications of TeV scale SU(4)xSU(2)_LxSU(2)_R quark-lepton unification

The alternative $SU(4) \otimes SU(2)_L \otimes SU(2)_R$ gauge model, which allows unification of the quarks and leptons at the TeV scale, is studied in detail. We discuss the implications for nucleon decay, B and K rare meson decays and neutrino masses. We also explain how this model solves the gauge hierarchy problem without using supersymmetry or extra large dimensions.

hep-ph↗
arXiv1999

Have mirror stars been observed?

Observations by the MACHO collaboration suggest that a significant proportion of the galactic halo dark matter is in the form of compact objects with typical masses $M\sim 0.5M_{\odot}$. One of the current mysteries is the nature and origin of these objects. We suggest that these objects are stars composed of mirror matter. This interpretation provides a plausible explanation for the inferred masses and abundance of the MACHO events. We also comment on the possibility of inferring the existence of mirror supernova's by detecting the neutrino burst in existing underground detectors such as SuperKamiokande.

astro-ph↗
arXiv1998

Implications of the $ν_μ\to ν_s$ solution to the atmospheric neutrino anomaly for early Universe cosmology

By numerically solving the quantum kinetic equations we compute the range of parameters where the $ν_μ\to ν_s$ oscillation solution to the atmospheric neutrino anomaly is consistent with a stringent big bang nucleosynthesis (BBN) bound of $N_{eff}^{BBN} \stackrel{<}{\sim} 3.6$. We show that this requires tau neutrino masses in the range $m_{ν_τ} \stackrel {>}{\sim} 4 eV$ (for $|δm^2_{atm}| = 10^{-2.5} eV^2$). We discuss the implications of this scenario for hot+cold dark matter, BBN, and the anisotropy of the cosmic microwave background.

hep-ph↗
arXiv1998

Atmospheric Neutrino Tests of Neutrino Oscillation Mechanisms

Recent Super-Kamiokande data on the atmospheric neutrino anomaly are used to test various mechanisms for neutrino oscillations. It is found that the current atmospheric neutrino data alone cannot rule out any particular mechanism. Future long-baseline experiments should play an important role in identifying the underlying neutrino oscillation mechanism.

hep-ph↗