arXiv subjects
Publications and source records attributed to A. Zee.
Euclidean quantum gravity is reconsidered, in the conformal mode approximation. Applying techniques from glass theory, we argue that the Euclidean partition function hides metastable states, which can be counted. This may reconcile conflicting results on the uniqueness of the de Sitter vacuum, and may be relevant to the cosmological constant problem.
We propose a new topological characterization of RNA secondary structures with pseudoknots based on two topological invariants. Starting from the classic arc-representation of RNA secondary structures, we consider a model that couples both I) the topological genus of the graph and II) the number of crossing arcs of the corresponding primitive graph. We add a term proportional to these topological invariants to the standard free energy of the RNA molecule, thus obtaining a novel free energy parametrization which takes into account the abundance of topologies of RNA pseudoknots observed in RNA databases.
We exploit a recent advance in the study of topological superconductors to propose a solution to the family puzzle of particle physics in the context of SO(18) (or more correctly, Spin(18)) grand unification. We argue that Yukawa couplings of intermediate strength may allow the mirror matter and extra families to decouple at arbitrarily high energies. As was clear from the existing literature, we have to go beyond the Higgs mechanism in order to solve the family puzzle. A pattern of symmetry breaking which results in the SU(5) grand unified theory with horizontal or family symmetry USp(4) = Spin(5) (or more loosely, SO(5)) leaves exactly three light families of matter and seems particularly appealing. We comment briefly on an alternative scheme involving discrete non-abelian family symmetries. In a few lengthy appendices we review some of the pertinent condensed matter theory.
Learned et. al. proposed that a sufficiently advanced extra-terrestrial civilization may tickle Cepheid and RR Lyrae variable stars with a neutrino beam at the right time, thus causing them to trigger early and jogging the otherwise very regular phase of their expansion and contraction. This would turn these stars into beacons to transmit information throughout the galaxy and beyond. The idea is to search for signs of phase modulation (in the regime of short pulse duration) and patterns, which could be indicative of intentional, omnidirectional signaling. We have performed such a search among variable stars using photometric data from the Kepler space telescope. In the RRc Lyrae star KIC 5520878, we have found two such regimes of long and short pulse durations. The sequence of period lengths, expressed as time series data, is strongly auto correlated, with correlation coefficients of prime numbers being significantly higher ($p=99.8$\%). Our analysis of this candidate star shows that the prime number oddity originates from two simultaneous pulsation periods and is likely of natural origin. Simple physical models elucidate the frequency content and asymmetries of the KIC 5520878 light curve. Despite this SETI null result, we encourage testing other archival and future time-series photometry for signs of modulated stars. This can be done as a by-product to the standard analysis, and even partly automated.
We document the presence of a few Cepheid and RR Lyrae variable stars with previously unrecognized characteristics. These stars exhibit the property of a period ratio of main pulsation divided by secondary pulsation P1/P2 very close to sqrt(2). Other stars of these types have period ratios which do not show clustering with a close association and a single remarkable non-harmonic number. Close examination reveals a deviation of multiples of a few times ~0.06% for these stars. This deviation seems to be present in discrete steps on the order of ~0.000390(4), indicating the possible presence of a sort of fine structure in this oscillation.
We use the discrete group Σ(81) = (Z_3 x Z_3 x Z_3)\rtimes Z_3 to explore a particular region of parameter space in the Private Higgs model. In doing so we suggest a relation among the off-diagonal entries of the neutrino mass matrix and a possible explanation for the muon magnetic moment anomaly, a_μ^{exp}-a_μ^{SM} ~ 10^{-9}. We predict three new nearly degenerate Higgs doublets with masses of order ~ 500 GeV to ~ 1 TeV, and three nearly degenerate SM-singlet TeV-scale neutrinos. The largest scale in the model is ~ 10 TeV, so there is no severe hierarchy problem. The appendix is devoted to the group theory of Σ(81).
The A4 x U(1) flavor model of He, Keum, and Volkas is extended to provide a minimal modification to tribimaximal mixing that accommodates a nonzero reactor angle theta13 ~ 0.1. The sequestering problem is circumvented by forbidding superheavy scales and large coupling constants which would otherwise generate sizable RG flows. The model is compatible with (but does not require) a stable or metastable dark matter candidate in the form of a complex scalar field with unit charge under a discrete subgroup Z4 of the U(1) flavor symmetry.
We present a global study of the simplest scalar phantom dark matter model. The best fit parameters of the model are determined by simultaneously imposing (i) relic density constraint from WMAP, (ii) 225 live days data from direct experiment XENON100, (iii) upper limit of gamma-ray flux from Fermi-LAT indirect detection based on dwarf spheroidal satellite galaxies, and (iv) the Higgs boson candidate with a mass about 125 GeV and its invisible branching ratio no larger than 40% if the decay of the Higgs boson into a pair of dark matter is kinematically allowed. The allowed parameter space is then used to predict annihilation cross sections for gamma-ray lines, event rates for three processes mono-b jet, single charged lepton and two charged leptons plus missing energies at the Large Hadron Collider, as well as to evaluate the muon anomalous magnetic dipole moment for the model.
We study the LHC phenomenology of a general class of "Private Higgs" (PH) models, in which fermions obtain their masses from their own Higgs doublets with $\op(1)$ Yukawa couplings, and the mass hierarchy is translated into a dynamical chain of vacuum expectation values. This is accomplished by introducing a number of light gauge-singlet scalars, the "darkons," some of which could play the role of dark matter. These models allow for substantial modifications to the decays of the lightest Higgs boson, for instance through mixing with TeV-scale PH fields and light darkons: the simplest version of the model predicts the ratios of partial widths to satisfy $\G(h \to VV^*)_{\text{PH}}/\G(h \to VV^*)_{\text{SM}} \approx \G(h \to \g\g)_{\text{PH}}/\G(h \to \g\g)_{\text{SM}} \leq 1$ and $\G(h \to b\bar b)_{\text{PH}}/\G(h \to b\bar b)_{\text{SM}} \sim \op(1)$, where the inequalities are saturated only in the absence of Higgs mixing with light darkons. An extension of the model proposed previously for generating nonzero neutrino masses can also contribute substantially to $h \to \g\g$ without violating electroweak precision constraints. If the Higgs coupling to fermions is found to deviate from the Standard Model (SM) expectation, then the PH model may be a viable candidate for extending the SM.
It is consistent with the measurement of θ_13 ~ 0.15 by Daya Bay to suppose that, in addition to being unitary, the neutrino mixing matrix is also almost hermitian, and thereby only a small perturbation from diag(+1,-1,-1) in a suitable basis. We suggest this possibility simply as an easily falsifiable ansatz that has not already been studied, as well as to offer a potentially useful means of organizing the experimental data. We explore the phenomenological implications of this ansatz and parametrize one type of deviation from the leading order relation |V_e3| \approx |V_τ1|. We also emphasize the group-invariant angle between orthogonal matrices as a means of comparing to data. The discussion is purely phenomenological, without any attempt to derive the condition V† \approx V from a fundamental theory.
We show that the Frobenius group $T_{13} = Z_{13} \rtimes Z_3$ is a suitable family symmetry group to study neutrino oscillations. Our approach is to catalog all possibilities within an effective field theory approach, assuming only SU(2)xU(1) supplemented by family symmetry. We will use tribimaximal mixing as a guide to place a constraint on the otherwise various possibilities. This leads to an exact fit between the neutrino and charged lepton sector. Such a fit has not been achieved with any other group so far. The results of this paper may then be useful in future studies on the compatibility of this Frobenius group with other models and mechanisms.
We explore some ways of minimally modifying the neutrino mixing matrix from tribimaximal, characterized by introducing at most one mixing angle and a CP violating phase thus extending our earlier work. One minimal modification, motivated to some extent by group theoretic considerations, is a simple case with the elements $V_{\alpha 2}$ of the second column in the mixing matrix equal to $1/\sqrt{3}$. Modifications by keeping one of the columns or one of the rows unchanged from tri-bimaximal mixing all belong to the class of minimal modification. Some of the cases have interesting experimentally testable consequences. In particular, the T2K and MINOS collaborations have recently reported indications of a non-zero $\theta_{13}$. For the cases we consider, the new data sharply constrain the CP violating phase angle $\delta$, with $\delta$ close to 0 (in some cases) and $\pi$ disfavored.
Motivated by the possibility that the amplitude for neutrinoless double beta decay may be much smaller than the planned sensitivity of future experiments, we study ansatze for the neutrino mass matrix with $M_{ee} = 0$. For the case in which CP is conserved, we consider two classes of real-valued mass matrices: "Class I" defined by $|M_{eμ}| = |M_{eτ}|$, and "Class II" defined by $|M_{μμ}| = |M_{ττ}|$. The important phenomenological distinction between the two is that Class I permits only "small" values of $V_{e3}$ up to $\sim 0.03$, while Class II admits "large" values of $V_{e3}$ up to its empirical upper limit of 0.22. Then we introduce CP-violating complex phases into the mass matrix. We show that it is possible to have tribimaximal mixing with $M_{ee} = 0$ and $|M_{μτ}| = |M_{μμ}| = |M_{ττ}|$ if the Majorana phase angles are $\pmπ/4$. Alternatively, for smaller values of $|M_{μτ}| = |M_{μμ}| = |M_{ττ}|$ it is possible to obtain $|V_{e3}| \sim 0.2$ and generate relatively large CP-violating amplitudes. To eliminate phase redundancy, we emphasize rephasing any mass matrix with $M_{ee} = 0$ into a standard form with two complex phases. The discussion alternates between analytical and numerical but remains purely phenomenological, without any attempt to derive mass matrices from a fundamental theory.
In the spirit of a previous study of the tetrahedral group $T \simeq A_4$, we discuss a minimalist scheme to derive the neutrino mixing matrix using the double tetrahedral group $T'$, the double cover of $T$. The new features are three distinct 2-dimensional representations and complex Clebsch-Gordan coefficients, which can result in a geometric source of CP violation in the neutrino mass matrix. In an appendix, we derive explicitly the relevant group theory for the tetrahedral group $T$ and its double cover $T'$.
Talk given by one of us (A. Zee) at Murray Gell-Mann's 80th Birthday Celebration held in Singapore, February 2010. Based on R. A. Porto and A. Zee, Class. Quant. Grav. 27, 065006 (2010) [arXiv:0910.3716 [hep-th]]
We speculate on the dynamical critical behavior of gravity in the extreme ultra-infrared (EuIR) sector and a mechanism to relax the cosmological constant. We show that in the EuIR the cosmological constant term could be made irrelevant for values of the dynamical critical exponent z_EuIR greater than one. We discuss a possible realization of this idea that connects the relaxation of the cosmological constant to the ratio between the EuIR and IR scales, where the latter serves as the 'UV' cutoff of our (ultra long distance) effective theory, with z_IR ~ 1. For distances smaller than the IR regime Lorentz invariance emerges. We entertain the possibility that the effective description of the universe may not be Lorentz invariant at much larger scales. We discuss why local physics cannot detect the 'natural' value for the density of dark energy below the IR scale, and briefly comment on possible connections with holography.
We examine the possibility to employ neutrinos to communicate within the galaxy. We discuss various issues associated with transmission and reception, and suggest that the resonant neutrino energy near 6.3 PeV may be most appropriate. In one scheme we propose to make Z^o particles in an overtaking e^+ - e^- collider such that the resulting decay neutrinos are near the W^- resonance on electrons in the laboratory. Information is encoded via time structure of the beam. In another scheme we propose to use a 30 PeV pion accelerator to create neutrino or anti-neutrino beams. The latter encodes information via the particle/anti-particle content of the beam, as well as timing. Moreover, the latter beam requires far less power, and can be accomplished with presently foreseeable technology. Such signals from an advanced civilization, should they exist, will be eminently detectable in neutrino detectors now under construction.
We introduce Higgs democracy in the Yukawa sector by constructing a model with a private Higgs and a dark scalar for each fermion thus addressing the large hierarchy among fermion masses. The model has interesting implications for the LHC, while the Standard Model phenomenology is recovered at low energies. We discuss some phenomenological implications such as FCNC, new Higgses at the TeV scale and dark matter candidates.