Scalar Quarks at the Large Hadron Collider

The properties of scalar quarks are studied, especially the formation of fermionic mesons with an anti-quark. On the basis of this theoretical investigation together with the experimental data, both from last year and from this year, of the ATLAS Collaboration and the CMS Collaboration at the Large Hadron Collider, it is proposed that the standard model of Glashow, Weinberg, and Salam should be augmented by scalar quarks, scalar leptons, and additional fermions. If these scalar quarks and scalar leptons are in one-to-one correspondence with the ordinary quarks and ordinary leptons, either in number or in the degrees of freedom, then there may be a fermion-boson symmetry. The fermion-boson symmetry obtained this way is of a different nature from that of supersymmetry.Comment: 7 pages, 1 figur

Quark production, Bose-Einstein condensates and thermalization of the quark-gluon plasma

In this paper, we study the thermalization of gluons and N_f flavors of massless quarks and antiquarks in a spatially homogeneous system. First, two coupled transport equations for gluons and quarks (and antiquarks) are derived within the diffusion approximation of the Boltzmann equation, with only 2 2 processes included in the collision term. Then, these transport equations are solved numerically in order to study the thermalization of the quark-gluon plasma. At initial time, we assume that no quarks or antiquarks are present and we choose the gluon distribution in the form f = f_0 theta (1-p/Q_s) with Q_s the saturation momentum and f_0 a constant. The subsequent evolution of systems may, or may not, lead to the formation of a (transient) Bose condensate, depending on the value of f_0. In fact, we observe, depending on the value of f_0, three different patterns: (a) thermalization without gluon Bose-Einstein condensate (BEC) for f_0 < f_{0t}, (b) thermalization with transient BEC for f_{0t} < f_0 < f_{0c}, and (c) thermalization with BEC for f_{0c} < f_0. The values of f_{0t} and f_{0c} depend on N_f. When f_0> 1 > f_{0c}, the onset of BEC occurs at a finite time t_c ~ 1/((alpha_s f_0)^2 Q_s). We also find that quark production slows down the thermalization process: the equilibration time for N_f = 3 is typically about 5 to 6 times longer than that for N_f = 0 at the same Q_s.Comment: 32 pages, 25 figures, minor modifications, Final version published in NP

Device-independent parallel self-testing of two singlets

Device-independent self-testing is the possibility of certifying the quantum state and the measurements, up to local isometries, using only the statistics observed by querying uncharacterized local devices. In this paper, we study parallel self-testing of two maximally entangled pairs of qubits: in particular, the local tensor product structure is not assumed but derived. We prove two criteria that achieve the desired result: a double use of the Clauser-Horne-Shimony-Holt inequality and the $3\times 3$ Magic Square game. This demonstrate that the magic square game can only be perfectly won by measureing a two-singlets state. The tolerance to noise is well within reach of state-of-the-art experiments.Comment: 9 pages, 2 figure

Quantum cluster approach to the spinful Haldane-Hubbard model

We study the spinful fermionic Haldane-Hubbard model at half filling using a combination of quantum cluster methods: cluster perturbation theory (CPT), the variational cluster approximation (VCA), and cluster dynamical mean-field theory (CDMFT). We explore possible zero-temperature phases of the model as a function of on-site repulsive interaction strength and next-nearest-neighbor hopping amplitude and phase. Our approach allows us to access the regime of intermediate interaction strength, where charge fluctuations are significant and effective spin model descriptions may not be justified. Our approach also improves upon mean-field solutions of the Haldane-Hubbard model by retaining local quantum fluctuations and treating them nonperturbatively. We find a correlated topological Chern insulator for weak interactions and a topologically trivial N\'eel antiferromagnetic insulator for strong interactions. For intermediate interactions, we find that topologically nontrivial N\'eel antiferromagnetic insulating phases and/or a topologically nontrivial nonmagnetic insulating phase may be stabilized.Comment: 11 pages, 12 figures. Published versio

On the Stability Domain of Systems of Three Arbitrary Charges

We present results on the stability of quantum systems consisting of a negative charge $-q_1$ with mass $m_{1}$ and two positive charges $q_2$ and $q_3$, with masses $m_{2}$ and $m_{3}$, respectively. We show that, for given masses $m_{i}$, each instability domain is convex in the plane of the variables $(q_{1}/q_{2}, q_{1}/q_{3})$. A new proof is given of the instability of muonic ions $(\alpha, p, \mu^-)$. We then study stability in some critical regimes where $q_3\ll q_2$: stability is sometimes restricted to large values of some mass ratios; the behaviour of the stability frontier is established to leading order in $q_3/q_2$. Finally we present some conjectures about the shape of the stability domain, both for given masses and varying charges, and for given charges and varying masses.Comment: Latex, 24 pages, 14 figures (some in latex, some in .eps

Implementing fault tolerant applications using reflective object-oriented programming

Abstract: Shows how reflection and object-oriented programming can be used to ease the implementation of classical fault tolerance mechanisms in distributed applications. When the underlying runtime system does not provide fault tolerance transparently, classical approaches to implementing fault tolerance mechanisms often imply mixing functional programming with non-functional programming (e.g. error processing mechanisms). The use of reflection improves the transparency of fault tolerance mechanisms to the programmer and more generally provides a clearer separation between functional and non-functional programming. The implementations of some classical replication techniques using a reflective approach are presented in detail and illustrated by several examples, which have been prototyped on a network of Unix workstations. Lessons learnt from our experiments are drawn and future work is discussed

Yang-Mills theory for non-semisimple groups

For semisimple groups, possibly multiplied by U(1)'s, the number of Yang-Mills gauge fields is equal to the number of generators of the group. In this paper, it is shown that, for non-semisimple groups, the number of Yang-Mills fields can be larger. These additional Yang-Mills fields are not irrelevant because they appear in the gauge transformations of the original Yang-Mills fields. Such non-semisimple Yang-Mills theories may lead to physical consequences worth studying. The non-semisimple group with only two generators that do not commute is studied in detail.Comment: 16 pages, no figures, prepared with ReVTeX

Why does wurtzite form in nanowires of III-V zinc-blende semiconductors?

We develop a nucleation-based model to explain the formation of the wurtzite (WZ) crystalline phase during the vapor-liquid-solid growth of free-standing nanowires of zinc-blende (ZB) semiconductors. We first show that, in nanowires, nucleation generally occurs at the outer edge of the solid/liquid interface (the triple phase line) rather than elsewhere at the solid/liquid interface. In the present case, this entails major differences between ZB and WZ nuclei. Depending on the pertinent interface energies, WZ nucleation is favored at high liquid supersaturation. This explains our systematic observation of ZB during the early stages of nanowire growth.Comment: 4 pages with 4 figures Submitted to Physical Review Letter