3,675 research outputs found
Quantum computation with devices whose contents are never read
In classical computation, a "write-only memory" (WOM) is little more than an
oxymoron, and the addition of WOM to a (deterministic or probabilistic)
classical computer brings no advantage. We prove that quantum computers that
are augmented with WOM can solve problems that neither a classical computer
with WOM nor a quantum computer without WOM can solve, when all other resource
bounds are equal. We focus on realtime quantum finite automata, and examine the
increase in their power effected by the addition of WOMs with different access
modes and capacities. Some problems that are unsolvable by two-way
probabilistic Turing machines using sublogarithmic amounts of read/write memory
are shown to be solvable by these enhanced automata.Comment: 32 pages, a preliminary version of this work was presented in the 9th
International Conference on Unconventional Computation (UC2010
Two Simple W' Models for the Early LHC
W' gauge bosons are good candidates for early LHC discovery. We define two
reference models, one containing a W'_R and one containing a W'_L, which may
serve as ``simplified models'' for presenting experimental results of W'
searches at the LHC. We present the Tevatron bounds on each model and compute
the constraints from precision electroweak observables. We find that indirect
low-energy constraints on the W'_L are quite strong. However, for a W'_R
coupling to right-handed fermions there exists a sizeable region in parameter
space beyond the bounds from the Tevatron and low-energy precision measurements
where even 50 inverse picobarns of integrated LHC luminosity are sufficient to
discover the W'_R. The most promising final states are two leptons and two
jets, or one lepton recoiling against a ``neutrino jet''. A neutrino jet is a
collimated object consisting of a hard lepton and two jets arising from the
decay of a highly boosted massive neutrino.Comment: 20 pages, 8 figures. v2: references adde
LEDAkem: a post-quantum key encapsulation mechanism based on QC-LDPC codes
This work presents a new code-based key encapsulation mechanism (KEM) called
LEDAkem. It is built on the Niederreiter cryptosystem and relies on
quasi-cyclic low-density parity-check codes as secret codes, providing high
decoding speeds and compact keypairs. LEDAkem uses ephemeral keys to foil known
statistical attacks, and takes advantage of a new decoding algorithm that
provides faster decoding than the classical bit-flipping decoder commonly
adopted in this kind of systems. The main attacks against LEDAkem are
investigated, taking into account quantum speedups. Some instances of LEDAkem
are designed to achieve different security levels against classical and quantum
computers. Some performance figures obtained through an efficient C99
implementation of LEDAkem are provided.Comment: 21 pages, 3 table
General Gauge and Anomaly Mediated Supersymmetry Breaking in Grand Unified Theories with Vector-Like Particles
In Grand Unified Theories (GUTs) from orbifold and various string
constructions the generic vector-like particles do not need to form complete
SU(5) or SO(10) representations. To realize them concretely, we present
orbifold SU(5) models, orbifold SO(10) models where the gauge symmetry can be
broken down to flipped SU(5) X U(1)_X or Pati-Salam SU(4)_C X SU(2)_L X SU(2)_R
gauge symmetries, and F-theory SU(5) models. Interestingly, these vector-like
particles can be at the TeV-scale so that the lightest CP-even Higgs boson mass
can be lifted, or play the messenger fields in the Gauge Mediated Supersymmetry
Breaking (GMSB). Considering GMSB, ultraviolet insensitive Anomaly Mediated
Supersymmetry Breaking (AMSB), and the deflected AMSB, we study the general
gaugino mass relations and their indices, which are valid from the GUT scale to
the electroweak scale at one loop, in the SU(5) models, the flipped SU(5) X
U(1)_X models, and the Pati-Salam SU(4)_C X SU(2)_L X SU(2)_R models. In the
deflected AMSB, we also define the new indices for the gaugino mass relations,
and calculate them as well. Using these gaugino mass relations and their
indices, we may probe the messenger fields at intermediate scale in the GMSB
and deflected AMSB, determine the supersymmetry breaking mediation mechanisms,
and distinguish the four-dimensional GUTs, orbifold GUTs, and F-theory GUTs.Comment: RevTex4, 45 pages, 15 tables, version to appear in JHE
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
Long Lived Fourth Generation and the Higgs
A chiral fourth generation is a simple and well motivated extension of the
standard model, and has important consequences for Higgs phenomenology. Here we
consider a scenario where the fourth generation neutrinos are long lived and
have both a Dirac and Majorana mass term. Such neutrinos can be as light as 40
GeV and can be the dominant decay mode of the Higgs boson for Higgs masses
below the W-boson threshold. We study the effect of the Majorana mass term on
the Higgs branching fractions and reevaluate the Tevatron constraints on the
Higgs mass. We discuss the prospects for the LHC to detect the semi-invisible
Higgs decays into fourth generation neutrino pairs. Under the assumption that
the lightest fourth generation neutrino is stable, it's thermal relic density
can be up to 20% of the observed dark matter density in the universe. This is
in agreement with current constraints on the spin dependent neutrino-neutron
cross section, but can be probed by the next generation of dark matter direct
detection experiments.Comment: v1: 19 pages, 5 figures; v2: References added; v3: version to appear
in JHE
Topological mechanochemistry of graphene
In view of a formal topology, two common terms, namely, connectivity and
adjacency, determine the quality of C-C bonds of sp2 nanocarbons. The feature
is the most sensitive point of the inherent topology of the species so that
such external action as mechanical deformation should obviously change it and
result in particular topological effects. The current paper describes the
effects caused by uniaxial tension of a graphene molecule in due course of a
mechanochemical reaction. Basing on the molecular theory of graphene, the
effects are attributed to both mechanical loading and chemical modification of
edge atoms of the molecule. The mechanical behavior is shown to be not only
highly anisotropic with respect to the direction of the load application, but
greatly dependent on the chemical modification of the molecule edge atoms thus
revealing topological character of the graphene deformation.Comment: 9 pages, 10 figures, 1 table. arXiv admin note: text overlap with
arXiv:1301.094
An Empirical Comparison of Information-Theoretic Criteria in Estimating the Number of Independent Components of fMRI Data
BACKGROUND: Independent Component Analysis (ICA) has been widely applied to the analysis of fMRI data. Accurate estimation of the number of independent components of fMRI data is critical to reduce over/under fitting. Although various methods based on Information Theoretic Criteria (ITC) have been used to estimate the intrinsic dimension of fMRI data, the relative performance of different ITC in the context of the ICA model hasn't been fully investigated, especially considering the properties of fMRI data. The present study explores and evaluates the performance of various ITC for the fMRI data with varied white noise levels, colored noise levels, temporal data sizes and spatial smoothness degrees. METHODOLOGY: Both simulated data and real fMRI data with varied Gaussian white noise levels, first-order auto-regressive (AR(1)) noise levels, temporal data sizes and spatial smoothness degrees were carried out to deeply explore and evaluate the performance of different traditional ITC. PRINCIPAL FINDINGS: Results indicate that the performance of ITCs depends on the noise level, temporal data size and spatial smoothness of fMRI data. 1) High white noise levels may lead to underestimation of all criteria and MDL/BIC has the severest underestimation at the higher Gaussian white noise level. 2) Colored noise may result in overestimation that can be intensified by the increase of AR(1) coefficient rather than the SD of AR(1) noise and MDL/BIC shows the least overestimation. 3) Larger temporal data size will be better for estimation for the model of white noise but tends to cause severer overestimation for the model of AR(1) noise. 4) Spatial smoothing will result in overestimation in both noise models. CONCLUSIONS: 1) None of ITC is perfect for all fMRI data due to its complicated noise structure. 2) If there is only white noise in data, AIC is preferred when the noise level is high and otherwise, Laplace approximation is a better choice. 3) When colored noise exists in data, MDL/BIC outperforms the other criteria
Inclusive double-quarkonium production at the Large Hadron Collider
Based on the nonrelativistic QCD (NRQCD) factorization formalism, we
investigate inclusive productions of two spin-triplet S-wave quarkonia
pp->2J/psi+X, 2Upsilon+X, and J/psi+Upsilon+X at the CERN Large Hadron
Collider. The total production rates integrated over the rapidity (y) and
transverse-momentum (p_T) ranges |y|<2.4 and p_T<50 GGeV are predicted to be
sigma[pp->2J/psi+X] = 22 (35) nb, sigma[pp->2Upsilon+X] = 24 (49) pb, and
sigma[pp->J/psi+Upsilon+X] = 7 (13) pb at the center-of-momentum energy sqrt{s}
= 7 (14) TeV. In order to provide predictions that can be useful in both small-
and large-p_T regions, we do not employ the fragmentation approximation and we
include the spin-triplet S-wave color-singlet and color-octet channels for each
quarkonium final state at leading order in the strong coupling. The p_T
distributions of pp->2J/psi+X and 2Upsilon+X in the low-p_T region are
dominated by the color-singlet contributions. At leading order in the strong
coupling, the color-singlet channel is absent for pp->J/psi+Upsilon+X.
Therefore, the process pp->J/psi+Upsilon+X may provide a useful probe to the
color-octet mechanism of NRQCD.Comment: 26 pages, 7 figures, 3 tables, version published in JHE
A Comprehensive Analysis of Electric Dipole Moment Constraints on CP-violating Phases in the MSSM
We analyze the constraints placed on individual, flavor diagonal CP-violating
phases in the minimal supersymmetric extension of the Standard Model (MSSM) by
current experimental bounds on the electric dipole moments (EDMs) of the
neutron, Thallium, and Mercury atoms. We identify the four CP-violating phases
that are individually highly constrained by current EDM bounds, and we explore
how these phases and correlations among them are constrained by current EDM
limits. We also analyze the prospective implications of the next generation of
EDM experiments. We point out that all other CP-violating phases in the MSSM
are not nearly as tightly constrained by limits on the size of EDMs. We
emphasize that a rich set of phenomenological consequences is potentially
associated with these generically large EDM-allowed phases, ranging from B
physics, electroweak baryogenesis, and signals of CP-violation at the CERN
Large Hadron Collider and at future linear colliders. Our numerical study takes
into account the complete set of contributions from one- and two-loop EDMs of
the electron and quarks, one- and two-loop Chromo-EDMs of quarks, the Weinberg
3-gluon operator, and dominant 4-fermion CP-odd operator contributions,
including contributions which are both included and not included yet in the
CPsuperH2.0 package. We also introduce an open-source numerical package, 2LEDM,
which provides the complete set of two-loop electroweak diagrams contributing
to the electric dipole moments of leptons and quarks.Comment: 23 pages, 11 figures; v2: references added, minor change
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