Galaxy growth in the concordance Λ\LambdaCDM cosmology

We use galaxy and dark halo data from the public database for the Millennium Simulation to study the growth of galaxies in the De Lucia et al. (2006) model for galaxy formation. Previous work has shown this model to reproduce many aspects of the systematic properties and the clustering of real galaxies, both in the nearby universe and at high redshift. It assumes the stellar masses of galaxies to increase through three processes, major mergers, the accretion of smaller satellite systems, and star formation. We show the relative importance of these three modes to be a strong function of stellar mass and of redshift. Galaxy growth through major mergers depends strongly on stellar mass, but only weakly on redshift. Except for massive systems, minor mergers contribute more to galaxy growth than major mergers at all redshifts and at all stellar masses. For galaxies significantly less massive than the Milky Way, star formation dominates the growth at all epochs. For galaxies significantly more massive than the Milky Way, growth through mergers is the dominant process at all epochs. At a stellar mass of $6\times 10^{10}M_\odot$, star formation dominates at $z>1$ and mergers at later times. At every stellar mass, the growth rates through star formation increase rapidly with increasing redshift. Specific star formation rates are a decreasing function of stellar mass not only at $z=0$ but also at all higher redshifts. For comparison, we carry out a similar analysis of the growth of dark matter halos. In contrast to the galaxies, growth rates depend strongly on redshift, but only weakly on mass. They agree qualitatively with analytic predictions for halo growth.Comment: 11 pages, 6 figure

Uniqueness of nontrivially complete monotonicity for a class of functions involving polygamma functions

For $m,n\in\mathbb{N}$, let $f_{m,n}(x)=\bigr[\psi^{(m)}(x)\bigl]^2+\psi^{(n)}(x)$ on $(0,\infty)$. In the present paper, we prove using two methods that, among all $f_{m,n}(x)$ for $m,n\in\mathbb{N}$, only $f_{1,2}(x)$ is nontrivially completely monotonic on $(0,\infty)$. Accurately, the functions $f_{1,2}(x)$ and $f_{m,2n-1}(x)$ are completely monotonic on $(0,\infty)$, but the functions $f_{m,2n}(x)$ for $(m,n)\ne(1,1)$ are not monotonic and does not keep the same sign on $(0,\infty)$.Comment: 9 page

Spontaneous Relaxation of a Charge Qubit under Electrical Measurement

In this work we first derive a generalized conditional master equation for quantum measurement by a mesoscopic detector, then study the readout characteristics of qubit measurement where a number of new features are found. The work would in particular highlight the qubit spontaneous relaxation effect induced by the measurement itself rather than an external thermal bath.Comment: 4 pages, 2 figures; an error in Eq.(8) is correcte

Graphene kirigami as a platform for stretchable and tunable quantum dot arrays

The quantum transport properties of a graphene kirigami similar to those studied in recent experiments are calculated in the regime of elastic, reversible deformations. Our results show that, at low electronic densities, the conductance profile of such structures replicates that of a system of coupled quantum dots, characterized by a sequence of minibands and stop-gaps. The conductance and I-V curves have different characteristics in the distinct stages of elastic deformation that characterize the elongation of these structures. Notably, the effective coupling between localized states is strongly reduced in the small elongation stage, whereas in the large elongation regime the development of strong, localized pseudomagnetic field barriers can reinforce the coupling and reestablish resonant tunneling across the kirigami. This provides an interesting example of interplay between geometry and pseudomagnetic field-induced confinement. The alternating miniband and stop-gaps in the transmission lead to I-V characteristics with negative differential conductance in well defined energy/doping ranges. These effects should be stable in a realistic scenario that includes edge roughness and Coulomb interactions, as these are expected to further promote localization of states at low energies in narrow segments of graphene nanostructures.Comment: 10 pages, 10 figure

Generation of GHZ entangled states of photons in multiple cavities via a superconducting qutrit or an atom through resonant interaction

We propose an efficient method to generate a GHZ entangled state of n photons in n microwave cavities (or resonators) via resonant interaction to a single superconducting qutrit. The deployment of a qutrit, instead of a qubit, as the coupler enables us to use resonant interactions exclusively for all qutrit-cavity and qutrit-pulse operations. This unique approach significantly shortens the time of operation which is advantageous to reducing the adverse effects of qutrit decoherence and cavity decay on fidelity of the protocol. Furthermore, the protocol involves no measurement on either the state of qutrit or cavity photons. We also show that the protocol can be generalized to other systems by replacing the superconducting qutrit coupler with different types of physical qutrit, such as an atom in the case of cavity QED, to accomplish the same task.Comment: 11 pages, 5 figures, accepted by Phys. Rev.