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R. R. Volkas

Publications and source records attributed to R. R. Volkas.

At least 55 records · Page 3Linked to original sources
arXiv1996

The exact parity symmetric model and big bang nucleosynthesis

The assumption of exact, unbroken parity symmetry leads directly to a simple predictive resolution of the atmospheric and solar neutrino puzzles. This is because the existence of this symmetry implies the existence of a set of mirror neutrinos which must mix maximally with the known neutrinos if neutrinos have mass. The maximal mixing of the electron neutrino with the mirror electron neutrino with $3 \times 10^{-10} eV^2 < |δm^2| < 10^{-3} eV^2$ eads to a predicted reduction of the solar neutrino flux by a factor of 2, which is in quite good agreement with the experiments. The maximal mixing of the muon neutrino with the mirror muon neutrino with $|δm^2| \simeq 10^{-2} eV^2$ also solves the atmospheric neutrino puzzle. We show that there is a significant range of parameters where these solutions are not in conflict with standard Big Bang Nucleosynthesis when the creation of lepton asymmetry due to neutrino oscillations is taken into account.

hep-ph↗
arXiv1996

Baryogenesis from baryon number violating scalar interactions

In the following work we consider the possibility of explaining the observed baryon number asymmetry in the universe from simple baryon number violating modifications, involving massive scalar bosons, to the Standard Model. In these cases baryon number violation is mediated through a combination of Yukawa and scalar self-coupling interactions. Starting with a previously compiled catalogue of baryon-number violating extensions of the Standard Model, we identify the minimal subsets which can induce a $B-L$ asymmetry and thus be immune to sphaleron washout. For each of these models, we identify the region of parameter space that leads to the production of a baryon number asymmetry of the correct order of magnitude.

hep-ph↗
arXiv1996

Studies of neutrino asymmetries generated by ordinary-sterile neutrino oscillations in the early universe and implications for big bang nucleosynthesis bounds

Ordinary-sterile neutrino oscillations can generate a significant lepton number asymmetry in the early Universe. We study this phenomenon in detail. We show that the dynamics of ordinary-sterile neutrino oscillations in the early Universe can be approximately described by a single integro-differential equation which we derive from both the density matrix and Hamiltonian formalisms. This equation reduces to a relatively simple ordinary first order differential equation if the system is sufficiently smooth (static limit). We study the conditions for which the static limit is an acceptable approximation. We also study the effect of the thermal distribution of neutrino momenta on the generation of lepton number. We apply these results to show that it is possible to evade (by many orders of magnitude) the Big Bang Nucleosynthesis (BBN) bounds on the mixing parameters, $δm^2$ and $\sin^2 2θ_0$, describing ordinary-sterile neutrino oscillations. We show that the large angle or maximal vacuum oscillation solution to the solar neutrino problem does not significantly modify BBN for most of the parameter space of interest, provided that the tau and/or mu neutrinos have masses greater than about 1 eV. We also show that the large angle or maximal ordinary-sterile neutrino oscillation solution to the atmospheric neutrino anomaly does not significantly modify BBN for a range of parameters.

hep-ph↗
arXiv1996

Electric charge quantisation from gauge invariance of a Lagrangian: A catalogue of baryon number violating scalar interactions

In gauge theories like the standard model, the electric charges of the fermions can be heavily constrained from the classical structure of the theory and from the cancellation of anomalies. There is however mounting evidence suggesting that these anomaly constraints are not as well motivated as the classical constraints. In light of this we discuss possible modifications of the minimal standard model which will give us complete electric charge quantisation from classical constraints alone. Because these modifications to the standard model involve the consideration of baryon number violating scalar interactions, we present a complete catalogue of the simplest ways to modify the standard model so as to introduce explicit baryon number violation. This has implications for proton decay searches and baryogenesis.

hep-ph↗
arXiv1996

Quaternionic Formulation of the Exact Parity Model

The exact parity model (EPM) is a simple extension of the Standard Model which reinstates parity invariance as an unbroken symmetry of nature. The mirror matter sector of the model can interact with ordinary matter through gauge boson mixing, Higgs boson mixing and, if neutrinos are massive, through neutrino mixing. The last effect has experimental support through the observed solar and atmospheric neutrino anomalies. In this paper we show that the exact parity model can be formulated in a quaternionic framework. This suggests that the idea of mirror matter and exact parity may have profound implications for the mathematical formulation of quantum theory.

hep-th↗
arXiv1995

Neutrino physics and the mirror world: how exact parity symmetry explains the solar neutrino deficit, the atmospheric neutrino anomaly and the LSND experiment

Evidence for $\bar ν_μ \rightarrow \bar ν_e$ oscillations has been reported at LAMPF using the LSND detector. Further evidence for neutrino mixing comes from the solar neutrino deficit and the atmospheric neutrino anomaly. All of these anomalies require new physics. We show that all of these anomalies can be explained if the standard model is enlarged so that an unbroken parity symmetry can be defined. This explanation holds independently of the actual model for neutrino masses. Thus, we argue that parity symmetry is not only a beautiful candidate for a symmetry beyond the standard model, but it can also explain the known neutrino physics anomalies.

hep-ph↗
arXiv1995

Reconciling sterile neutrinos with big bang nucleosynthesis

We re-examine the big bang nucleosynthesis (BBN) bounds on the mixing of neutrinos with sterile species. These bounds depend on the assumption that the relic neutrino asymmetry $L_ν$ is very small. We show that for $L_ν$ large enough (greater than about $10^{-5}$) the standard BBN bounds do not apply. We apply this result to the sterile neutrino solution to the atmospheric neutrino anomaly and show that for $L_ν > 7 \times 10^{-5}$ it is consistent with BBN. The BBN bounds on sterile neutrinos mixing with electron neutrinos can also be weakened considerably.

hep-ph↗
arXiv1995

Maximal neutrino oscillation solution to the solar neutrino problem

We discuss a simple predictive solution to the solar neutrino problem based on maximal vacuum neutrino oscillations. The solution can be motivated by the exact parity symmetric model which predicts that the neutrino mass eigenstates are maximal mixtures of ordinary and mirror weak eigenstates (if neutrinos are massive). We show that this proposed solution to the solar neutrino problem is in reasonable agreement with the experiments, and that in the near future this scheme may be either ruled out or tested more precisely as statistics improve for the SAGE and GALLEX experiments. Predictions are also given for the upcoming Superkamiokande, SNO and Borexino experiments.

hep-ph↗
arXiv1995

Large neutrino asymmetries from neutrino oscillations

We re-examine neutrino oscillations in the early universe. Contrary to previous studies, we show that large neutrino asymmetries can arise due to oscillations between ordinary neutrinos and sterile neutrinos. This means that the Big Bang Nucleosynthesis (BBN) bounds on the mass and mixing of ordinary neutrinos with sterile neutrinos can be evaded. Also, it is possible that the neutrino asymmetries can be large (i.e. $\stackrel{>}{\sim} 10\%$), and hence have a significant effect on BBN through nuclear reaction rates.

hep-ph↗
arXiv1995

New issues in quark-lepton symmetry

Two models incorporating different forms of spontaneously broken quark-lepton symmetry are discussed. Both models are constructed so that quark-lepton symmetry can be broken at as low an energy scale as phenomenology allows, thus maximising their testability. The first model uses the Pati-Salam gauge group SU(4)$\otimes$SU(2)$_L\otimes$SU(2)$_R$. The main analysis presented here concerns large threshold corrections to the $m_b = m_τ$ tree-level mass relation. The second model is a new and simplified theory using discrete quark-lepton symmetry which has a very economical Higgs sector and elegantly avoids a potential quark-lepton mass relation problem.

hep-ph↗
arXiv1995

Prospects for mass unification at low energy scales

A simple Pati-Salam SU(4) model with a low symmetry breaking scale of about 1000 TeV is presented. The analysis concentrates on calculating radiative corrections to tree-level mass relations for third generation fermions. The tree-level relation $m_b/m_τ=1$ predicted by such models can receive large radiative corrections up to about $50\%$ due to threshold effects at the mass unification scale. These corrections are thus of about the same importance as those that give rise to renormalisation group running. The high figure of $50\%$ can be achieved because 1-loop graphs involving the physical charged Higgs boson give corrections to $m_τ-m_b$ that are proportional to the large top quark mass. These corrections can either increase or decrease $m_b/m_τ$ depending on the value of an unknown parameter. They can also be made to vanish through a fine-tuning. A related model of tree-level $t$-$b$-$τ$ unification which uses the identification of SU(2)$_R$ with custodial SU(2) is then discussed. A curious relation $m_b \simeq \sqrt{2} m_τ$ is found to be satisfied at tree-level in this model. The overall conclusion of this work is that the tree-level relation $m_b = m_τ$ at low scales such as 1000 TeV or somewhat higher can produce a successful value for $m_b/m_τ$ after corrections, but one must be mindful that radiative corrections beyond those incorporated through the renormalisation group can be very important. This motivates that an on-going search for the rare decays $K^0_L \to μ^{\pm} e^{\mp}$ be maintained.

hep-ph↗
arXiv1995

New and improved quark-lepton symmetric models

We show how the use of a see-saw mechanism based on a $3 \times 3$ neutrino mass matrix texture can considerably simplify Higgs sectors for quark-lepton symmetric models (and for Standard Model extensions generally). The main theory we discuss also incorporates a previously considered scenario whereby the charged lepton of a particular generation is necessarily less massive than the corresponding charge $+2/3$ quark, provided intergenerational mixing is small.

hep-ph↗
arXiv1994

From $m_{d}=m_{e}$ to Realistic Mass Relations in Quark-Lepton Symmetric Models

In recent years a new potential symmetry of fundamental particle physics has been investigated --- discrete quark-lepton symmetry. When this symmetry is implemented, however, it often leads to either of the unrealistic predictions $m_{u}=m_{e}$ or $m_{d}=m_{e}$. This paper considers two possible ways models based on $m_{d}=m_{e}$ can be made realistic.

hep-ph↗
arXiv1994

Possible reason why leptons are lighter than quarks

The minimal model of spontaneously broken leptonic colour and discrete quark-lepton symmetry predicts that charged leptons have the same masses as their partner charge $+2/3$ quarks up to small radiative corrections. By invoking a different pattern of symmetry breaking, a similar model can be constructed with the structural feature that charged leptons have to be lighter than their partner quarks because of mixing between leptonic colours, provided mixing between generations is not too strong. As well as furnishing a new model-building tool, this is phenomenologically interesting because some of the new physics responsible for the quark-lepton mass hierarchy could exist on scales as low as several hundred GeV.

hep-ph↗
arXiv1994

Phenomenology of the Two Higgs Doublet Sector of a Quark-Lepton Symmetric Model

In the simplest examples of models with a discrete quark-lepton symmetry, an electroweak symmetry breaking sector with more than one Higgs doublet is necessary to obtain the correct mass relations between quarks and leptons. A two Higgs doublet model has flavour-nonconserving Yukawa couplings, which are proportional to the masses of the quark-lepton symmetric partners of the fermions. We describe how flavour changing leptonic decays can occur, with branching ratios not far beyond that currently measureable, enabling investigation of the phenomenology of such models.

hep-ph↗
arXiv1994

Model for a Light Z' Boson

A model of a light $Z'$ boson is constructed and phenomenological bounds are derived. This $Z'$ boson arises from a very simple extension to the Standard Model, and it is constrained to be light because the vacuum expectation values which generate its mass also break the electroweak gauge group. It is difficult to detect experimentally because it couples exclusively or primarily (depending on symmetry breaking details) to second and third generation leptons. However, if the $Z'$ boson is sufficiently light, then there exists the possibility of the two-body decay $τ\rightarrow μZ'$ occuring. This will provide a striking signature to test the model.

hep-ph↗
arXiv1993

Effective Lagrangian Approach to the Fermion Mass Problem

An effective theory is proposed, combining the standard gauge group $SU(3)_{C}\otimes SU(2)_{L}\otimes U(1)_{Y}$ with a horizontal discrete symmetry. By assigning appropriate charges under this discrete symmetry to the various fermion fields and to (at least) two Higgs doublets, the broad spread of the fermion mass and mixing angle spectrum can be explained as a result of suppressed, non-renormalisable terms. A particular model is constructed which achieves the above while simultaneously suppressing neutral Higgs-induced flavour-changing processes.

hep-ph↗