21,006 research outputs found
Optimal Charge and Color Breaking conditions in the MSSM
In the MSSM, we make a careful tree-level study of Charge and Color Breaking
conditions in the plane , focusing on the top
quark scalar case. A simple and fast procedure to compute the VEVs of the
dangerous vacuum is presented and used to derive a model-independent optimal
CCB bound on . This bound takes into account all possible deviations of
the CCB vacuum from the D-flat directions. For large , it provides
a CCB maximal mixing for the stop scalar fields ,
which automatically rules out the Higgs maximal mixing . As a result, strong limits on the stop mass spectrum and a
reduction, in some cases substantial, of the one-loop upper bound on the
CP-even lightest Higgs boson mass, , are obtained. To incorporate one-loop
leading corrections, this tree-level CCB condition should be evaluated at an
appropriate renormalization scale which proves to be the SUSY scale.Comment: 41 pages, 7 eps figures, minor corrections, references added, to
appear in Nucl. Phys.
Flavour-Dependent Type II Leptogenesis
We reanalyse leptogenesis via the out-of-equilibrium decay of the lightest
right-handed neutrino in type II seesaw scenarios, taking into account
flavour-dependent effects. In the type II seesaw mechanism, in addition to the
type I seesaw contribution, an additional direct mass term for the light
neutrinos is present. We consider type II seesaw scenarios where this
additional contribution arises from the vacuum expectation value of a Higgs
triplet, and furthermore an effective model-independent approach. We
investigate bounds on the flavour-specific decay asymmetries, on the mass of
the lightest right-handed neutrino and on the reheat temperature of the early
universe, and compare them to the corresponding bounds in the type I seesaw
framework. We show that while flavour-dependent thermal type II leptogenesis
becomes more efficient for larger mass scale of the light neutrinos, and the
bounds become relaxed, the type I seesaw scenario for leptogenesis becomes more
constrained. We also argue that in general, flavour-dependent effects cannot be
ignored when dealing with leptogenesis in type II seesaw models.Comment: 19 pages, 8 figures; v3: minor additions, typos corrected, results
and conclusions unchange
Carving Out the Space of 4D CFTs
We introduce a new numerical algorithm based on semidefinite programming to
efficiently compute bounds on operator dimensions, central charges, and OPE
coefficients in 4D conformal and N=1 superconformal field theories. Using our
algorithm, we dramatically improve previous bounds on a number of CFT
quantities, particularly for theories with global symmetries. In the case of
SO(4) or SU(2) symmetry, our bounds severely constrain models of conformal
technicolor. In N=1 superconformal theories, we place strong bounds on
dim(Phi*Phi), where Phi is a chiral operator. These bounds asymptote to the
line dim(Phi*Phi) <= 2 dim(Phi) near dim(Phi) ~ 1, forbidding positive
anomalous dimensions in this region. We also place novel upper and lower bounds
on OPE coefficients of protected operators in the Phi x Phi OPE. Finally, we
find examples of lower bounds on central charges and flavor current two-point
functions that scale with the size of global symmetry representations. In the
case of N=1 theories with an SU(N) flavor symmetry, our bounds on current
two-point functions lie within an O(1) factor of the values realized in
supersymmetric QCD in the conformal window.Comment: 60 pages, 22 figure
Dependent randomized rounding for clustering and partition systems with knapsack constraints
Clustering problems are fundamental to unsupervised learning. There is an
increased emphasis on fairness in machine learning and AI; one representative
notion of fairness is that no single demographic group should be
over-represented among the cluster-centers. This, and much more general
clustering problems, can be formulated with "knapsack" and "partition"
constraints. We develop new randomized algorithms targeting such problems, and
study two in particular: multi-knapsack median and multi-knapsack center. Our
rounding algorithms give new approximation and pseudo-approximation algorithms
for these problems. One key technical tool, which may be of independent
interest, is a new tail bound analogous to Feige (2006) for sums of random
variables with unbounded variances. Such bounds are very useful in inferring
properties of large networks using few samples
A Geometric Approach to CP Violation: Applications to the MCPMFV SUSY Model
We analyze the constraints imposed by experimental upper limits on electric
dipole moments (EDMs) within the Maximally CP- and Minimally Flavour-Violating
(MCPMFV) version of the MSSM. Since the MCPMFV scenario has 6 non-standard
CP-violating phases, in addition to the CP-odd QCD vacuum phase \theta_QCD,
cancellations may occur among the CP-violating contributions to the three
measured EDMs, those of the Thallium, neutron and Mercury, leaving open the
possibility of relatively large values of the other CP-violating observables.
We develop a novel geometric method that uses the small-phase approximation as
a starting point, takes the existing EDM constraints into account, and enables
us to find maximal values of other CP-violating observables, such as the EDMs
of the Deuteron and muon, the CP-violating asymmetry in b --> s \gamma decay,
and the B_s mixing phase. We apply this geometric method to provide upper
limits on these observables within specific benchmark supersymmetric scenarios,
including extensions that allow for a non-zero \theta_QCD.Comment: 34 pages, 16 eps figures, to appear in JHE
Fast Parallel Randomized QR with Column Pivoting Algorithms for Reliable Low-rank Matrix Approximations
Factorizing large matrices by QR with column pivoting (QRCP) is substantially
more expensive than QR without pivoting, owing to communication costs required
for pivoting decisions. In contrast, randomized QRCP (RQRCP) algorithms have
proven themselves empirically to be highly competitive with high-performance
implementations of QR in processing time, on uniprocessor and shared memory
machines, and as reliable as QRCP in pivot quality.
We show that RQRCP algorithms can be as reliable as QRCP with failure
probabilities exponentially decaying in oversampling size. We also analyze
efficiency differences among different RQRCP algorithms. More importantly, we
develop distributed memory implementations of RQRCP that are significantly
better than QRCP implementations in ScaLAPACK.
As a further development, we introduce the concept of and develop algorithms
for computing spectrum-revealing QR factorizations for low-rank matrix
approximations, and demonstrate their effectiveness against leading low-rank
approximation methods in both theoretical and numerical reliability and
efficiency.Comment: 11 pages, 14 figures, accepted by 2017 IEEE 24th International
Conference on High Performance Computing (HiPC), awarded the best paper priz
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