514 research outputs found
Characterising New Physics Models by Effective Dimensionality of Parameter Space
We show that the dimension of the geometric shape formed by the
phenomenologically valid points inside a multi-dimensional parameter space can
be used to characterise different new physics models and to define a
quantitative measure for the distribution of the points. We explain a simple
algorithm to determine the box-counting dimension from a given set of parameter
points, and illustrate our method with examples from different models that have
recently been studied with respect to precision flavour observables.Comment: 14 pages, 8 figure
Particle-Antiparticle Mixing, epsilon_K, Delta Gamma_q, A_SL^q, A_CP(B_d -> psi K_S), A_CP(B_s -> psi phi) and B -> X_{s,d} gamma in the Littlest Higgs Model with T-Parity
We calculate a number of observables related to particle-antiparticle mixing
in the Littlest Higgs model with T-parity (LHT). The resulting effective
Hamiltonian for Delta F=2 transitions agrees with the one of Hubisz et al., but
our phenomenological analysis goes far beyond the one of these authors. In
particular, we point out that the presence of mirror fermions with new flavour
and CP-violating interactions allows to remove the possible Standard Model (SM)
discrepancy between the CP asymmetry S_{psi K_S} and large values of |V_ub| and
to obtain for the mass difference Delta M_s < (Delta M_s)_SM as suggested by
the recent result by the CDF collaboration. We also identify a scenario in
which simultaneously significant enhancements of the CP asymmetries S_{phi psi}
and A_SL^q relative to the SM are possible, while satisfying all existing
constraints, in particular from the B -> X_s gamma decay and A_CP(B -> X_s
gamma) that are presented in the LHT model here for the first time. In another
scenario the second, non-SM, value for the angle gamma=-(109+-6) from tree
level decays, although unlikely, can be made consistent with all existing data
with the help of mirror fermions. We present a number of correlations between
the observables in question and study the implications of our results for the
mass spectrum and the weak mixing matrix of mirror fermions. In the most
interesting scenarios, the latter one turns out to have a hierarchical
structure that differs significantly from the CKM one.Comment: 51 pages, 20 figures, 1 table. Extended discussion of the phases in
the new mixing matrix V_Hd, some references added or updated, conclusions
unchanged. Final version published in JHE
Spin Measurements in Cascade Decays at the LHC
We systematically study the possibility of determining the spin of new
particles after their discovery at the LHC. We concentrate on angular
correlations in cascade decays. Motivated by constraints of electroweak
precision tests and the potential of providing a Cold Dark Matter candidate, we
focus on scenarios of new physics in which some discrete symmetry guarantees
the existence of stable neutral particles which escape the detector. More
specifically, we compare supersymmetry with another generic scenario in which
new physics particles have the same spin as their Standard Model partners. A
survey of possibilities of observing spin correlations in a broad range of
decay channels is carried out, with interesting ones identified. Rather than
confining ourselves to one "collider friendly" benchmark point (such as SPS1a),
we describe the parameter region in which any particular decay channel is
effective. We conduct a more detailed study of chargino's spin determination in
the decay channel . A scan
over the chargino and neutralino masses is performed. We find that as long as
the spectrum is not too degenerate the prospects for spin determination in this
channel are rather good.Comment: 36 pages, references added, 1 figure modifie
CP Violation in D0 - anti-D0 Oscillations: General Considerations and Applications to the Littlest Higgs Model with T-Parity
The observed D0 - anti-D0 oscillations provide a new stage in our search for
New Physics in heavy flavour dynamics. The theoretical verdict on the observed
values of x_D and y_D remains ambiguous: while they could be totally generated
by Standard Model dynamics, they could also contain a sizable or even leading
contribution from New Physics. Those oscillations are likely to enhance the
observability of CP violation as clear manifestations of New Physics. We
present general formulae for D0 - anti-D0 oscillations, concentrating on the
case of negligible direct CP violation. In particular we derive a general
formula for the time-dependent mixing-induced CP asymmetry in decays to a CP
eigenstate and its correlation with the semileptonic CP asymmetry a_SL(D0) in
D0(t) -> l nu K. We apply our formalism to the Littlest Higgs model with
T-parity, using the time-dependent CP asymmetry in D -> K_S phi as an example.
We find observable effects at a level well beyond anything possible with CKM
dynamics. Comparisons with CP violation in the K and B systems offer an
excellent test of this scenario and reveal the specific pattern of flavour and
CP violation in the D0 - anti-D0 system predicted by this model. We discuss a
number of charm decays that could potentially offer an insight in the dynamics
of CP violation in D decays. We also apply our formalism to B_s - anti-B_s
mixing.Comment: 26 pages, 9 png figures, 1 table. v2: eq. (A.1) corrected, minor
clarifying comments and few references added. v3: typos corrected, matches
published versio
On the Standard Model prediction for BR(B{s,d} to mu+ mu-)
The decay Bs to mu+ mu- is one of the milestones of the flavor program at the
LHC. We reappraise its Standard Model prediction. First, by analyzing the
theoretical rate in the light of its main parametric dependence, we highlight
the importance of a complete evaluation of higher-order electroweak
corrections, at present known only in the large-mt limit, and leaving sizable
dependence on the definition of electroweak parameters. Using insights from a
complete calculation of such corrections for K to pi bar{nu} nu decays, we find
a scheme in which NLO electroweak corrections are likely to be negligible.
Second, we address the issue of the correspondence between the initial and the
final state detected by the experiments, and those used in the theoretical
prediction. Particular attention is devoted to the effect of the soft
radiation, that has not been discussed for this mode in the previous
literature, and that can lead to O(10%) corrections to the decay rate. The
"non-radiative" branching ratio (that is equivalent to the branching ratio
fully inclusive of bremsstrahlung radiation) is estimated to be (3.23 +/- 0.27)
x 10^{-9} for the flavor eigenstate, with the main uncertainty resulting from
the value of f_{Bs}, followed by the uncertainty due to higher order
electroweak corrections. Applying the same strategy to Bd to mu+ mu-, we find
for its non-radiative branching ratio (1.07 +/- 0.10) x 10^{-10}.Comment: 15 pages. v3: very minor changes to match the journal version (EPJC
Genital warts and infection with human immunodeficiency virus in high-risk women in Burkina Faso: a longitudinal study
BACKGROUND: Human papillomaviruses are the most common sexually transmitted infections, and genital warts, caused by HPV-6 and 11, entail considerable morbidity and cost. The natural history of genital warts in relation to HIV-1 infection has not been described in African women. We examined risk factors for genital warts in a cohort of high-risk women in Burkina Faso, in order to further describe their epidemiology. METHODS: A prospective study of 765 high-risk women who were followed at 4-monthly intervals for 27 months in Burkina Faso. Logistic and Cox regression were used to identify factors associated with prevalent, incident and persistent genital warts, including HIV-1 serostatus, CD4+ count, and concurrent sexually transmitted infections. In a subset of 306 women, cervical HPV DNA was tested at enrollment. RESULTS: Genital wart prevalence at baseline was 1.6% (8/492) among HIV-uninfected and 7.0% (19/273) among HIV-1 seropositive women. Forty women (5.2%) experienced at least one incident GW episode. Incidence was 1.1 per 100 person-years among HIV-uninfected women, 7.4 per 100 person-years among HIV-1 seropositive women with a nadir CD4+ count >200 cells/ΌL and 14.6 per 100 person-years among HIV-1 seropositive women with a nadir CD4+ count †200 cells/ΌL. Incident genital warts were also associated with concurrent bacterial vaginosis, and genital ulceration. Antiretroviral therapy was not protective against incident or persistent genital warts. Detection of HPV-6 DNA and abnormal cervical cytology were strongly associated with incident genital warts. CONCLUSIONS: Genital warts occur much more frequently among HIV-1 infected women in Africa, particularly among those with low CD4+ counts. Antiretroviral therapy did not reduce the incidence or persistence of genital warts in this population
in Littlest Higgs Model
The inclusive process is studied in the littlest Higgs
model. The contributions arising from new particles are normally suppressed by
a factor of . Due to the large uncertainties of experimental
measurements and theoretical predictions, the model parameters can escape from
the constraints of present experiments provided TeV.Comment: 7 pages, 1 fi
Oxidised cosmic acceleration
We give detailed proofs of several new no-go theorems for constructing flat
four-dimensional accelerating universes from warped dimensional reduction.
These new theorems improve upon previous ones by weakening the energy
conditions, by including time-dependent compactifications, and by treating
accelerated expansion that is not precisely de Sitter. We show that de Sitter
expansion violates the higher-dimensional null energy condition (NEC) if the
compactification manifold M is one-dimensional, if its intrinsic Ricci scalar R
vanishes everywhere, or if R and the warp function satisfy a simple limit
condition. If expansion is not de Sitter, we establish threshold
equation-of-state parameters w below which accelerated expansion must be
transient. Below the threshold w there are bounds on the number of e-foldings
of expansion. If M is one-dimensional or R everywhere vanishing, exceeding the
bound implies the NEC is violated. If R does not vanish everywhere on M,
exceeding the bound implies the strong energy condition (SEC) is violated.
Observationally, the w thresholds indicate that experiments with finite
resolution in w can cleanly discriminate between different models which satisfy
or violate the relevant energy conditions.Comment: v2: corrections, references adde
Fermion Masses and Mixings in the Little Flavon Model
We present a complete analysis of the fermion masses and mixing matrices in
the framework of the little flavon model. In this model textures are generated
by coupling the fermions to scalar fields, the little flavons, that are
pseudo-Goldstone bosons of the breaking of a global SU(6) symmetry. The Yukawa
couplings arise from the vacuum expectation values of the flavon fields, their
sizes controlled by a potential a la Coleman-Weinberg. Quark and lepton mass
hierarchies and mixing angles are accomodated within the effective approach in
a natural manner.Comment: 11 pages, RevTeX4, version to appear on Phys. Rev.
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