95,032 research outputs found
Strong CP and Mu Problems in Theories with Gauge Mediated Supersymmetry Breaking
We provide a simple solution to the and strong CP problems in the
context of gauge mediated supersymmetry breaking. The generic appearance of R
symmetry in dynamical supersymmetry breaking is used to implement Peccei-Quinn
symmetry. Acceptable and terms as well as the large symmetry breaking
scale are induced in the presence of nonrenormalizable interactions.
Cosmological consequences of this scheme turn out to yield constraints on the
PQ symmetry breaking scale and the number of the messenger/heavy quarks.
Complexity in introducing non-R Peccei-Quinn symmetry is contrasted with the
case of R symmetry.Comment: 10 pages, Revtex. Significantly modified version to apear in Phys.
Rev.
Ultrafast Dynamics of Vibrational Symmetry Breaking in a Charge-ordered Nickelate
The ability to probe symmetry breaking transitions on their natural time
scales is one of the key challenges in nonequilibrium physics. Stripe ordering
represents an intriguing type of broken symmetry, where complex interactions
result in atomic-scale lines of charge and spin density. Although phonon
anomalies and periodic distortions attest the importance of electron-phonon
coupling in the formation of stripe phases, a direct time-domain view of
vibrational symmetry breaking is lacking. We report experiments that track the
transient multi-THz response of the model stripe compound
LaSrNiO, yielding novel insight into its electronic and
structural dynamics following an ultrafast optical quench. We find that
although electronic carriers are immediately delocalized, the crystal symmetry
remains initially frozen - as witnessed by time-delayed suppression of
zone-folded Ni-O bending modes acting as a fingerprint of lattice symmetry.
Longitudinal and transverse vibrations react with different speeds, indicating
a strong directionality and an important role of polar interactions. The hidden
complexity of electronic and structural coupling during stripe melting and
formation, captured here within a single terahertz spectrum, opens new paths to
understanding symmetry breaking dynamics in solids.Comment: 21 pages, 4 figures; updated version with journal re
On The Complexity and Completeness of Static Constraints for Breaking Row and Column Symmetry
We consider a common type of symmetry where we have a matrix of decision
variables with interchangeable rows and columns. A simple and efficient method
to deal with such row and column symmetry is to post symmetry breaking
constraints like DOUBLELEX and SNAKELEX. We provide a number of positive and
negative results on posting such symmetry breaking constraints. On the positive
side, we prove that we can compute in polynomial time a unique representative
of an equivalence class in a matrix model with row and column symmetry if the
number of rows (or of columns) is bounded and in a number of other special
cases. On the negative side, we show that whilst DOUBLELEX and SNAKELEX are
often effective in practice, they can leave a large number of symmetric
solutions in the worst case. In addition, we prove that propagating DOUBLELEX
completely is NP-hard. Finally we consider how to break row, column and value
symmetry, correcting a result in the literature about the safeness of combining
different symmetry breaking constraints. We end with the first experimental
study on how much symmetry is left by DOUBLELEX and SNAKELEX on some benchmark
problems.Comment: To appear in the Proceedings of the 16th International Conference on
Principles and Practice of Constraint Programming (CP 2010
Running of Fermion Observables in Non-Supersymmetric SO(10) Models
We investigate the complete renormalization group running of fermion
observables in two different realistic non-supersymmetric models based on the
gauge group with intermediate symmetry breaking for both
normal and inverted neutrino mass orderings. Contrary to results of previous
works, we find that the model with the more minimal Yukawa sector of the
Lagrangian fails to reproduce the measured values of observables at the
electroweak scale, whereas the model with the more extended Yukawa sector can
do so if the neutrino masses have normal ordering. The difficulty in finding
acceptable fits to measured data is a result of the added complexity from the
effect of an intermediate symmetry breaking as well as tension in the value of
the leptonic mixing angle .Comment: 15 pages, 3 figures, 4 tables. Final version published in JHE
Distributed Symmetry Breaking in Hypergraphs
Fundamental local symmetry breaking problems such as Maximal Independent Set
(MIS) and coloring have been recognized as important by the community, and
studied extensively in (standard) graphs. In particular, fast (i.e.,
logarithmic run time) randomized algorithms are well-established for MIS and
-coloring in both the LOCAL and CONGEST distributed computing
models. On the other hand, comparatively much less is known on the complexity
of distributed symmetry breaking in {\em hypergraphs}. In particular, a key
question is whether a fast (randomized) algorithm for MIS exists for
hypergraphs.
In this paper, we study the distributed complexity of symmetry breaking in
hypergraphs by presenting distributed randomized algorithms for a variety of
fundamental problems under a natural distributed computing model for
hypergraphs. We first show that MIS in hypergraphs (of arbitrary dimension) can
be solved in rounds ( is the number of nodes of the
hypergraph) in the LOCAL model. We then present a key result of this paper ---
an -round hypergraph MIS algorithm in
the CONGEST model where is the maximum node degree of the hypergraph
and is any arbitrarily small constant.
To demonstrate the usefulness of hypergraph MIS, we present applications of
our hypergraph algorithm to solving problems in (standard) graphs. In
particular, the hypergraph MIS yields fast distributed algorithms for the {\em
balanced minimal dominating set} problem (left open in Harris et al. [ICALP
2013]) and the {\em minimal connected dominating set problem}. We also present
distributed algorithms for coloring, maximal matching, and maximal clique in
hypergraphs.Comment: Changes from the previous version: More references adde
Quenched Computation of the Complexity of the Sherrington-Kirkpatrick Model
The quenched computation of the complexity in the
Sherrington-Kirkpatrick model is presented. A modified Full Replica
Symmetry Breaking Ansatz is introduced in order to study the complexity
dependence on the free energy. Such an Ansatz corresponds to require
Becchi-Rouet-Stora-Tyutin supersymmetry. The complexity computed this way is
the Legendre transform of the free energy averaged over the quenched disorder.
The stability analysis shows that this complexity is inconsistent at any free
energy level but the equilibirum one. The further problem of building a
physically well defined solution not invariant under supersymmetry and
predicting an extensive number of metastable states is also discussed.Comment: 19 pages, 13 figures. Some formulas added corrected, changes in
discussion and conclusion, one figure adde
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