Search

In analysing five dimensional orbifolds with exceptional gauge groups, we seek to find stable vacua configurations which satisfy the minimal requirements for asymptotic grand unified models. In this respect we show that no minimal asymptotic grand unified theory can be built. Our results point towards non-minimal models based on $E_6$: one featuring supersymmetry, and the other needing a modification of the Coleman-Weinberg potential to stabilise the breaking of $E_6$ to the standard model gauge group., Comment: 20 pages, 2 figures, 2 tables

The minimal $SO(10)$ grand unified theory, augmented by higher-dimensional operators, is based on the following Higgs representations: adjoint $45_{\rm H}$, spinor $16_{\rm H}$ and complex vector $10_{\rm H}$. It was recently realized that, as opposed to the conventional wisdom, any intermediate mass scale has to lie close to the grand unification one. This bears profound consequences for the scalar particles mass spectrum and the proton decay lifetime. A complete analysis of the parameter space shows the following interesting correlation under the requirement of perturbativity of the theory: A color octet below approximately $5\,\rm TeV$ would imply a lower bound on neutrino mass $m_{\nu}\gtrsim 0.2\,\rm eV$, soon to be probed, a scalar weak triplet below $500\,\rm GeV$ and a scalar weak doublet, color triplet below $3\,\rm TeV$. If one were to stick to no flavor cancellations in proton decay amplitudes, one would recover a recent result of all these states being accessible at collider energies. Moreover, the proton decay lifetime would then be tantalizingly close to the present experimental bound., Comment: 13 pages, 3 figures

We examine the vacuum stability of gauge symmetry breaking in five dimensions, compactified on the $S_1/(\mathbb{Z}_2 \times \mathbb{Z}'_2)$ orbifold. We consider $SU(N)$, $Sp(N)$, $SO(2N)$ and $SO(2N+1)$ theories in the bulk, and provide an exhaustive classification of possible parity assignments that lead to stable orbifolds and of the corresponding symmetry breaking patterns. We use these results in the search for viable asymptotic grand unification theories (aGUT), testing the stability criteria on models based on $SU(6)$ and $SU(8)$. As a result, we identify two viable aGUTs: a unique $SU(6)$ pathway down to the Standard Model, and one $SU(8)$ model leading to an intermediate Pati-Salam partial unification., Comment: 44 pages, 4 figures

We study the mass scales in the $SO(10)$ grand unified theory based on the following minimal Higgs representation content: adjoint $45_{\rm H}$, spinor $16_{\rm H}$ and complex vector $10_{\rm H}$, with higher dimensional operators on top of renormalizable interactions. We show that the consistency of the theory requires scalar $W$ and $Z$, scalar quark doublet and scalar gluon to lie below $ 10\, \rm TeV$ energy and potentially accessible even at the LHC. These signatures are intimately connected with the prediction of proton lifetime below $10^{35} {\rm yr}$, to be probed in the new generation of proton decay experiments., Comment: v3: published version in Phys. Lett. B. A few references and clarifications regarding Yukawa couplings and neutrino mass running added. Minor cosmetic changes made

The Cram\'er-Rao bound and the quantum Fisher information have been tools used extensively for interferometric phase sensitivity. Most scenarios considering a Mach-Zehnder interferometer with two input sources focused on the phase-matched case, when the Fisher information is maximal. Under this constraint, the best sensitivity is achieved for a balanced (50/50) input beam splitter. In this paper, we take a different approach: we allow the beam splitter transmission coefficient as well as the input phase mismatch to be variable parameters. We then search for a pair of these parameters that maximizes the Fisher information. We find that for the double coherent input the maximum Fisher information can always be reached in the unbalanced case for a carefully chosen input phase mismatch. For the coherent plus squeezed vacuum case we find that under certain circumstances a threshold phase mismatch exists, beyond which the optimum Fisher information is found for the degenerate case. For the squeezed-coherent plus squeezed vacuum case we find that the optimum actually occurs when the squeezing angles of the two inputs are in anti-phase., Comment: 11 pages, 7 figures

Interferometry is a widely-used technique for precision measurements in both classical and quantum contexts. One way to increase the precision of phase measurements, for example in a Mach-Zehnder interferometer (MZI), is to use high-intensity lasers. In this paper we study the phase sensitivity of a MZI in two detection setups (difference intensity detection and single-mode intensity detection) and for three input scenarios (coherent, double coherent and coherent plus squeezed vacuum). For the coherent and double coherent input, both detection setups can reach the quantum Cramer-Rao bound, although at different values of the optimal phase shift. The double coherent input scenario has the unique advantage of changing the optimal phase shift by varying the input power ratio., Comment: 10 pages, 9 figures