106 research outputs found
Un-oriented Quiver Theories for Majorana Neutrons
In the context of un-oriented open string theories, we identify quivers
whereby a Majorana mass for the neutron is indirectly generated by exotic
instantons. We discuss two classes of (Susy) Standard Model like quivers,
depending on the embedding of SU(2)_W in the Chan-Paton group. In both cases,
the main mechanism involves a vector-like pair mixing through a
non-perturbative mass term. We also discuss possible relations between the
phenomenology of Neutron-Antineutron oscillations and LHC physics in these
models. In particular, a vector-like pair of color-triplet scalars or
color-triplet fermions could be directly detected at LHC, compatibly with
n-\bar{n} limits. Finally we briefly comment on Pati-Salam extensions of our
models.Comment: More comments on phenomenology and fluxes, Re-discussion of
SM-quivers compatible with n-cycles conditions Version accepted by JHE
Neural Network Parameterizations of Electromagnetic Nucleon Form Factors
The electromagnetic nucleon form-factors data are studied with artificial
feed forward neural networks. As a result the unbiased model-independent
form-factor parametrizations are evaluated together with uncertainties. The
Bayesian approach for the neural networks is adapted for chi2 error-like
function and applied to the data analysis. The sequence of the feed forward
neural networks with one hidden layer of units is considered. The given neural
network represents a particular form-factor parametrization. The so-called
evidence (the measure of how much the data favor given statistical model) is
computed with the Bayesian framework and it is used to determine the best form
factor parametrization.Comment: The revised version is divided into 4 sections. The discussion of the
prior assumptions is added. The manuscript contains 4 new figures and 2 new
tables (32 pages, 15 figures, 2 tables
The Light Stop Scenario from Gauge Mediation
In this paper we embed the light stop scenario, a MSSM framework which
explains the baryon asymmetry of the universe through a strong first order
electroweak phase transition, in a top-down approach. The required low energy
spectrum consists in the light SM-like Higgs, the right-handed stop, the
gauginos and the Higgsinos while the remaining scalars are heavy. This spectrum
is naturally driven by renormalization group evolution starting from a heavy
scalar spectrum at high energies. The latter is obtained through a
supersymmetry-breaking mix of gauge mediation, which provides the scalars
masses by new gauge interactions, and gravity mediation, which generates
gaugino and Higgsino masses. This supersymmetry breaking also explains the \mu\
and B_\mu\ parameters necessary for electroweak breaking and predicts small
tri-linear mixing terms A_t in agreement with electroweak baryogenesis
requirements. The minimal embedding predicts a Higgs mass around its
experimental lower bound and by a small extension higher masses m_H\lesssim 127
GeV can be accommodated.Comment: 20 pages, 3 figures; v2: changes in the conventions; v3: more details
on the Higgs mass prediction, version published in JHE
Neutrinoless double beta decay in seesaw models
We study the general phenomenology of neutrinoless double beta decay in
seesaw models. In particular, we focus on the dependence of the neutrinoless
double beta decay rate on the mass of the extra states introduced to account
for the Majorana masses of light neutrinos. For this purpose, we compute the
nuclear matrix elements as functions of the mass of the mediating fermions and
estimate the associated uncertainties. We then discuss what can be inferred on
the seesaw model parameters in the different mass regimes and clarify how the
contribution of the light neutrinos should always be taken into account when
deriving bounds on the extra parameters. Conversely, the extra states can also
have a significant impact, cancelling the Standard Model neutrino contribution
for masses lighter than the nuclear scale and leading to vanishing neutrinoless
double beta decay amplitudes even if neutrinos are Majorana particles. We also
discuss how seesaw models could reconcile large rates of neutrinoless double
beta decay with more stringent cosmological bounds on neutrino masses.Comment: 34 pages, 5 eps figures and 1 axodraw figure. Final version published
in JHEP. NME results available in Appendi
Does zero temperature decide on the nature of the electroweak phase transition?
Taking on a new perspective of the electroweak phase transition, we investigate in detail the role played by the depth of the electroweak minimum (“vacuum energy difference”). We find a strong correlation between the vacuum energy difference and the strength of the phase transition. This correlation only breaks down if a negative eigen-value develops upon thermal corrections in the squared scalar mass matrix in the broken vacuum before the critical temperature. As a result the scalar fields slide across field space toward the symmetric vacuum, often causing a significantly weakened phase transition. Phenomenological constraints are found to strongly disfavour such sliding scalar scenarios. For several popular models, we suggest numerical bounds that guarantee a strong first order electroweak phase transition. The zero temperature phenomenology can then be studied in these parameter regions without the need for any finite temperature calculations. For almost all non-supersymmetric models with phenomenologically viable parameter points, we find a strong phase transition is guaranteed if the vacuum energy difference is greater than −8.8 × 107 GeV4. For the GNMSSM, we guarantee a strong phase transition for phenomenologically viable parameter points if the vacuum energy difference is greater than −6.9×107 GeV4. Alternatively, we capture more of the parameter space exhibiting a strong phase transition if we impose a simultaneous bound on the vacuum energy difference and the singlet mass
Neutron Majorana mass from exotic instantons
We show how a Majorana mass for the Neutron could result from
non-perturbative quantum gravity effects peculiar to string theory. In
particular, "exotic instantons" in un-oriented string compactifications with
D-branes extending the (supersymmetric) standard model could indirectly produce
an effective operator delta{m} n^t n+h.c. In a specific model with an extra
vector-like pair of `quarks', acquiring a large mass proportional to the string
mass scale (exponentially suppressed by a function of the string moduli
fields), delta{m} can turn out to be as low as 10^{-24}-10^{-25} eV. The
induced neutron-antineutron oscillations could take place with a time scale
tau_{n\bar{n}} > 10^8 s, that could be tested by the next generation of
experiments. On the other hand, proton decay and FCNC's are automatically
strongly suppressed and are compatible with the current experimental limits.
Depending on the number of brane intersections, the model may also lead to the
generation of Majorana masses for R-handed neutrini. Our proposal could also
suggest neutron-neutralino or neutron-axino oscillations, with implications in
UCN, Dark Matter Direct Detection, UHECR and Neutron-Antineutron oscillations.
This suggests to improve the limits on neutron-antineutron oscillations, as a
possible test of string theory and quantum gravity.Comment: 35 pages, 11 figures. More comments on neutron-neutralino mixin
Observation of the Baryonic Flavor-Changing Neutral Current Decay Lambda_b -> Lambda mu+ mu-
We report the first observation of the baryonic flavor-changing neutral
current decay Lambda_b -> Lambda mu+ mu- with 24 signal events and a
statistical significance of 5.8 Gaussian standard deviations. This measurement
uses ppbar collisions data sample corresponding to 6.8fb-1 at sqrt{s}=1.96TeV
collected by the CDF II detector at the Tevatron collider. The total and
differential branching ratios for Lambda_b -> Lambda mu+ mu- are measured. We
find B(Lambda_b -> Lambda mu+ mu-) = [1.73+-0.42(stat)+-0.55(syst)] x 10^{-6}.
We also report the first measurement of the differential branching ratio of B_s
-> phi mu+ mu- using 49 signal events. In addition, we report branching ratios
for B+ -> K+ mu+ mu-, B0 -> K0 mu+ mu-, and B -> K*(892) mu+ mu- decays.Comment: 8 pages, 2 figures, 4 tables. Submitted to Phys. Rev. Let
Neuroadaptations in Human Chronic Alcoholics: Dysregulation of the NF-κB System
Anna Ökvist is with Karolinska Institute, Sofia Johansson is with Karolinska Institute, Alexander Kuzmin is with Karolinska Institute, Igor Bazov is with Karolinska Institute, Roxana Merino-Martinez is with Karolinska Institute, Igor Ponomarev is with UT Austin, R. Dayne Mayfield is with UT Austin, R. Adron Harris is with UT Austin, Donna Sheedy is with University of Sydney, Therese Garrick is with University of Sydney, Clive Harper is with University of Sydney, Yasmin L. Hurd is with Mount Sinai School of Medicine, Lars Terenius is with Karolinska Institute, Tomas J. Ekström is with Karolinska Institute, Georgy Bakalkin is with Karolinska Institute and Uppsala University, Tatjana Yakovleva is with Karolinska Institute and Uppsala University.Background -- Alcohol dependence and associated cognitive impairments apparently result from neuroadaptations to chronic alcohol consumption involving changes in expression of multiple genes. Here we investigated whether transcription factors of Nuclear Factor-kappaB (NF-κB) family, controlling neuronal plasticity and neurodegeneration, are involved in these adaptations in human chronic alcoholics. Methods and Findings -- Analysis of DNA-binding of NF-κB (p65/p50 heterodimer) and the p50 homodimer as well as NF-κB proteins and mRNAs was performed in postmortem human brain samples from 15 chronic alcoholics and 15 control subjects. The prefrontal cortex involved in alcohol dependence and cognition was analyzed and the motor cortex was studied for comparison. The p50 homodimer was identified as dominant κB binding factor in analyzed tissues. NF-κB and p50 homodimer DNA-binding was downregulated, levels of p65 (RELA) mRNA were attenuated, and the stoichiometry of p65/p50 proteins and respective mRNAs was altered in the prefrontal cortex of alcoholics. Comparison of a number of p50 homodimer/NF-κB target DNA sites, κB elements in 479 genes, down- or upregulated in alcoholics demonstrated that genes with κB elements were generally upregulated in alcoholics. No significant differences between alcoholics and controls were observed in the motor cortex. Conclusions -- We suggest that cycles of alcohol intoxication/withdrawal, which may initially activate NF-κB, when repeated over years downregulate RELA expression and NF-κB and p50 homodimer DNA-binding. Downregulation of the dominant p50 homodimer, a potent inhibitor of gene transcription apparently resulted in derepression of κB regulated genes. Alterations in expression of p50 homodimer/NF-κB regulated genes may contribute to neuroplastic adaptation underlying alcoholism.This work was supported by grants from the AFA Forsäkring to AK, YLH, TJE and GB, the Research Foundation of the Swedish Alcohol Retail Monopoly (SRA) and Karolinska Institutet to AK, TJE and GB, and the Swedish Science Research Council and the Swedish National Drug Policy Coordinator to GB. The Australian Brain Donor Programs NSW Tissue Resource Centre was supported by The University of Sydney, National Health and Medical Research Council of Australia, Neuroscience Institute of Schizophrenia and Allied Disorders, National Institute of Alcohol Abuse and Alcoholism and NSW Department of Health.Waggoner Center for Alcohol and Addiction Researc
Measurements of the D-sJ resonance properties
We report measurements of the properties of the D-sJ(+)(2317) and D-sJ(+)(2457) resonances produced in continuum e(+)e(-) annihilation near roots=10.6 GeV. The analysis is based on an 86.9 fb(-1) data sample collected with the Belle detector at KEKB. We determine the masses to be M(D-sJ(+)(2317))=2317.2+/-0.5(stat)+/-0.9(syst) MeV/c(2) and M(D-sJ(+)(2457))=2456.5+/-1.3(stat)+/-1.3(syst) MeV/c(2). We observe the radiative decay mode D-sJ(+)(2457)-->D(s)(+)gamma and the dipion decay mode D-sJ(+)(2457)-->D(s)(+)pi(+)pi(-) and determine their branching fractions. No corresponding decays are observed for the D-sJ(2317) state. These results are consistent with the spin-parity assignments of 0(+) for the D-sJ(2317) and 1(+) for the D-sJ(2457)
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