11,461 research outputs found
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 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 with mass and two positive charges and
, with masses and , respectively. We show that, for given
masses , each instability domain is convex in the plane of the variables
. A new proof is given of the instability of muonic
ions . We then study stability in some critical regimes
where : stability is sometimes restricted to large values of some
mass ratios; the behaviour of the stability frontier is established to leading
order in . 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
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