521 research outputs found
Quintessence, inflation and baryogenesis from a single pseudo-Nambu-Goldstone boson
We exhibit a model in which a single pseudo-Nambu-Goldstone boson explains
dark energy, inflation and baryogenesis. The model predicts correlated signals
in future collider experiments, WIMP searches, proton decay experiments, dark
energy probes, and the PLANCK satellite CMB measurements.Comment: 16 pages, 3 color figure
Eviction of a 125 GeV "heavy"-Higgs from the MSSM
We prove that the present experimental constraints are already enough to rule
out the possibility of the ~125 GeV Higgs found at LHC being the second
lightest Higgs in a general MSSM context, even with explicit CP violation in
the Higgs potential. Contrary to previous studies, we are able to eliminate
this possibility analytically, using simple expressions for a relatively small
number of observables. We show that the present LHC constraints on the diphoton
signal strength, tau-tau production through Higgs and BR(B -> X_s gamma) are
enough to preclude the possibility of H_2 being the observed Higgs with m_H~125
GeV within an MSSM context, without leaving room for finely tuned
cancellations. As a by-product, we also comment on the difficulties of an MSSM
interpretation of the excess in the gamma-gamma production cross section
recently found at CMS that could correspond to a second Higgs resonance at
m_H~136 GeV.Comment: 38 pages, 9 figures. Final version accepted at JHEP. Sections 2, 3
and appendices simplified. Experimental results updated, several references
added. Small typos corrected and a new comparison of approximate formulas
with full expressions include
Self-accelerating solutions of scalar-tensor gravity
Scalar-tensor gravity is the simplest and best understood modification of
general relativity, consisting of a real scalar field coupled directly to the
Ricci scalar curvature. Models of this type have self-accelerating solutions.
In an example inspired by string dilaton couplings, scalar-tensor gravity
coupled to ordinary matter exhibits a de Sitter type expansion, even in the
presence of a {\it negative} cosmological constant whose magnitude exceeds that
of the matter density. This unusual behavior does not require phantoms, ghosts
or other exotic sources. More generally, we show that any expansion history can
be interpreted as arising partly or entirely from scalar-tensor gravity. To
distinguish any quintessence or inflation model from its scalar-tensor
variants, we use the fact that scalar-tensor models imply deviations of the
post-Newtonian parameters of general relativity, and time variation of the
Newton's gravitational coupling . We emphasize that next-generation probes
of modified GR and the time variation of are an essential complement to
dark energy probes based on luminosity-distance measurements.Comment: 14 pages, 3 figure
CPT Violation Implies Violation of Lorentz Invariance
An interacting theory that violates CPT invariance necessarily violates
Lorentz invariance. On the other hand, CPT invariance is not sufficient for
out-of-cone Lorentz invariance. Theories that violate CPT by having different
particle and antiparticle masses must be nonlocal.Comment: Minor changes in the published versio
Neutrino Physics, Superbeams, and the Neutrino Factory
We summarize what has been learned about the neutrino mass spectrum and
neutrino mixing, identify interesting open questions that can be answered by
accelerator neutrino facilities of the future, and discuss the importance and
physics of answering them.Comment: To appear in the Proceedings of the 4th International Workshop on
Neutrino Factories (Nu Fact 02). LaTeX, 10 pages, 1 eps figur
Short-Baseline Electron Neutrino Disappearance, Tritium Beta Decay and Neutrinoless Double-Beta Decay
We consider the interpretation of the MiniBooNE low-energy anomaly and the
Gallium radioactive source experiments anomaly in terms of short-baseline
electron neutrino disappearance in the framework of 3+1 four-neutrino mixing
schemes. The separate fits of MiniBooNE and Gallium data are highly compatible,
with close best-fit values of the effective oscillation parameters Delta m^2
and sin^2 2 theta. The combined fit gives Delta m^2 >~ 0.1 eV^2 and 0.11 <
sin^2 2 theta < 0.48 at 2 sigma. We consider also the data of the Bugey and
Chooz reactor antineutrino oscillation experiments and the limits on the
effective electron antineutrino mass in beta-decay obtained in the Mainz and
Troitsk Tritium experiments. The fit of the data of these experiments limits
the value of sin^2 2 theta below 0.10 at 2 sigma. Considering the tension
between the neutrino MiniBooNE and Gallium data and the antineutrino reactor
and Tritium data as a statistical fluctuation, we perform a combined fit which
gives Delta m^2 \simeq 2 eV and 0.01 < sin^2 2 theta < 0.13 at 2 sigma.
Assuming a hierarchy of masses m_1, m_2, m_3 << m_4, the predicted
contributions of m_4 to the effective neutrino masses in beta-decay and
neutrinoless double-beta-decay are, respectively, between about 0.06 and 0.49
and between about 0.003 and 0.07 eV at 2 sigma. We also consider the
possibility of reconciling the tension between the neutrino MiniBooNE and
Gallium data and the antineutrino reactor and Tritium data with different
mixings in the neutrino and antineutrino sectors. We find a 2.6 sigma
indication of a mixing angle asymmetry.Comment: 14 pages; final version published in Phys.Rev.D82:053005,201
Local demands on sterile neutrinos
In a model independent manner, we explore the local implications of a single
neutrino oscillation measurement which cannot be reconciled within a
three-neutrino theory. We examine this inconsistency for a single region of
baseline to neutrino energy . Assuming that sterile neutrinos account for
the anomaly, we find that the {\it local} demands of this datum can require the
addition to the theory of one to three sterile neutrinos. We examine the
constraints which can be used to determine when more than one neutrino would be
required. The results apply only to a given region of . The question of
the adequacy of the sterile neutrinos to satisfy a global analysis is not
addressed here. Finally, using the results of a 3+2 analysis, we indicate
values for unknown mixing matrix elements which would require two sterile
neutrinos due to local demands only.Comment: 11 pages, 1 figure, discussion adde
Constraining Models of New Physics in Light of Recent Experimental Results on
We study extensions of the Standard Model where the charged current weak
interactions are governed by the CKM matrix and where all tree-level decays are
dominated by their Standard Model contribution. We constrain both analytically
and numerically the ratio and the phase difference between the New Physics and
the Standard Model contributions to the mixing amplitude of the neutral
system using the experimental results on , ,
and . We present new results concerning models with minimal
flavor violation and update the relevant parameter space. We also study the
left-right symmetric model with spontaneously broken CP, probing the viability
of this model in view of the recent results for and other
observables.Comment: 32 pages, including 9 figures, typos and error in fig. 1 corrected,
minor modificiation in the text, conclusions unchanged, to appear in PR
Three-Flavour Neutrino-Mixing Implications of the LSND Result
The LSND result is shown to fit into a minimal three-flavour neutrino-mixing
scenario capable of describing all known experimental facts provided the large
Delta M^2 = m_3^2 - m_2^2 \sim m_3^2 - m_1^2 lies in the range 2.5 x 10^{-1} <
Delta M^2 < 3.0 eV^2. In this range the value of P_{\mu\tau} is expected to be
about 5% or larger.Comment: 10 pages, 2 eps figures, LaTeX 2.09, revised for Physics Letters
Minimal Noncanonical Cosmologies
We demonstrate how much it is possible to deviate from the standard
cosmological paradigm of inflation-assisted LambdaCDM, keeping within current
observational constraints, and without adding to or modifying any theoretical
assumptions. We show that within a minimal framework there are many new
possibilities, some of them wildly different from the standard picture. We
present three illustrative examples of new models, described phenomenologically
by a noncanonical scalar field coupled to radiation and matter. These models
have interesting implications for inflation, quintessence, reheating,
electroweak baryogenesis, and the relic densities of WIMPs and other exotics.Comment: 20 pages, 5 figures, 3 table
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