237 research outputs found
Stringent bounds to spatial variations of the electron-to-proton mass ratio in the Milky Way
The ammonia method to probe variations of the electron-to-proton mass ratio,
Delta_mu/mu, is applied for the first time to dense prestellar molecular clouds
in the Milky Way. Carefully selected sample of 21 NH_3/CCS pairs observed in
the Perseus molecular cloud provide the offset Delta V (CCS-NH_3)=
36+/-7_{stat}+/-13.5_{sys} m/s . A similar offset of Delta V = 40.8 +/-
12.9_{stat} m/s between NH_3 (J,K) = (1,1) and N_2H+ J = 1-0 has been found in
an isolated dense core L183 by Pagani et al. (2009). Overall these observations
provide a safe bound of a maximum offset between ammonia and the other
molecules at the level of Delta V < 100 m/s. This bound corresponds to
Delta_mu/mu < 1E-7, which is an order of magnitude more sensitive than
available extragalactic constraints. Taken at face value the measured Delta V
shows positive shifts between the line centers of NH_3 and these two other
molecules and suggest a real offset, which would imply a Delta_mu/mu about
4E-8. If Delta_mu/mu follows the gradient of the local gravitational potential,
then the obtained results are in conflict with laboratory atomic clock
experiments in the solar system by 5 orders of magnitude, thus requiring a
chameleon-type scalar field model. New measurements involving other molecules
and a wider range of objects along with verification of molecular rest
frequencies are currently planned to confirm these first indications.Comment: 7 pages +2 figures. Galileo Galilei Institute Conferences on Dark
Matter and Dark Energ
Oscillations of the F(R) dark energy in the accelerating universe
Oscillations of the dark energy around the phantom divide line,
, both during the matter era and also in the de Sitter epoch
are investigated. The analysis during the de Sitter epoch is revisited by
expanding the modified equations of motion around the de Sitter solution. Then,
during the matter epoch, the time dependence of the dark energy perturbations
is discussed by using two different local expansions. For high values of the
red shift, the matter epoch is a stable point of the theory, giving the
possibility to expand the -functions in terms of the dark energy
perturbations. In the late-time matter era, the realistic case is considered
where dark energy tends to a constant. The results obtained are confirmed by
precise numerical computation on a specific model of exponential gravity. A
novel and very detailed discussion is provided on the critical points in the
matter era and on the relation of the oscillations with possible singularities.Comment: 23 pages, 11 figures, version to appear in EPJ
Cosmic Acceleration in Brans-Dicke Cosmology
We consider Brans-Dicke theory with a self-interacting potential in Einstein
conformal frame. We show that an accelerating expansion is possible in a
spatially flat universe for large values of the Brans-Dicke parameter
consistent with local gravity experiments.Comment: 10 Pages, 3 figures, To appear in General Relativity and Gravitatio
Search for varying constants of nature from astronomical observation of molecules
The status of searches for possible variation in the constants of nature from
astronomical observation of molecules is reviewed, focusing on the
dimensionless constant representing the proton-electron mass ratio
. The optical detection of H and CO molecules with large
ground-based telescopes (as the ESO-VLT and the Keck telescopes), as well as
the detection of H with the Cosmic Origins Spectrograph aboard the Hubble
Space Telescope is discussed in the context of varying constants, and in
connection to different theoretical scenarios. Radio astronomy provides an
alternative search strategy bearing the advantage that molecules as NH
(ammonia) and CHOH (methanol) can be used, which are much more sensitive to
a varying than diatomic molecules. Current constraints are
for redshift , corresponding to
look-back times of 10-12.5 Gyrs, and for
, corresponding to half the age of the Universe (both at 3
statistical significance). Existing bottlenecks and prospects for future
improvement with novel instrumentation are discussed.Comment: Contribution to Workshop "High Performance Clocks in Space" at the
International Space Science Institute, Bern 201
Strong laser fields as a probe for fundamental physics
Upcoming high-intensity laser systems will be able to probe the
quantum-induced nonlinear regime of electrodynamics. So far unobserved QED
phenomena such as the discovery of a nonlinear response of the quantum vacuum
to macroscopic electromagnetic fields can become accessible. In addition, such
laser systems provide for a flexible tool for investigating fundamental
physics. Primary goals consist in verifying so far unobserved QED phenomena.
Moreover, strong-field experiments can search for new light but weakly
interacting degrees of freedom and are thus complementary to accelerator-driven
experiments. I review recent developments in this field, focusing on photon
experiments in strong electromagnetic fields. The interaction of
particle-physics candidates with photons and external fields can be
parameterized by low-energy effective actions and typically predict
characteristic optical signatures. I perform first estimates of the accessible
new-physics parameter space of high-intensity laser facilities such as POLARIS
and ELI.Comment: 7 pages, Key Lecture at the ELI Workshop and School on "Fundamental
Physics with Ultra-High Fields", 9 September - 2 October 2008 at Frauenworth
Monastery, German
gravity constrained by PPN parameters and stochastic background of gravitational waves
We analyze seven different viable -gravities towards the Solar System
tests and stochastic gravitational waves background. The aim is to achieve
experimental bounds for the theory at local and cosmological scales in order to
select models capable of addressing the accelerating cosmological expansion
without cosmological constant but evading the weak field constraints. Beside
large scale structure and galactic dynamics, these bounds can be considered
complimentary in order to select self-consistent theories of gravity working at
the infrared limit. It is demonstrated that seven viable -gravities under
consideration not only satisfy the local tests, but additionally, pass the
above PPN-and stochastic gravitational waves bounds for large classes of
parameters.Comment: 23 pages, 8 figure
Cosmic Evolution in a Modified Brans-Dicke Theory
We consider Brans-Dicke theory with a self-interacting potential in Einstein
conformal frame. We introduce a class of solutions in which an accelerating
expansion is possible in a spatially flat universe for positive and large
values of the Brans-Dicke parameter consistent with local gravity experiments.
In this Einstein frame formulation, the theory appears as an interacting
quintessence model in which the interaction term is given by the conformal
transformation. In such an interacting model, we shall show that the solutions
lead simultaneously to a constant ratio of energy densities of matter and the
scalar field.Comment: 11 pages, 3 figures, To appear in Astrophysics and Space Scienc
Some Observational Consequences of Brane World Cosmologies
The presence of dark energy in the Universe is inferred directly and
indirectly from a large body of observational evidence. The simplest and most
theoretically appealing possibility is the vacuum energy density (cosmological
constant). However, although in agreement with current observations, such a
possibility exacerbates the well known cosmological constant problem, requiring
a natural explanation for its small, but nonzero, value. In this paper we focus
our attention on another dark energy candidate, one arising from gravitational
\emph{leakage} into extra dimensions. We investigate observational constraints
from current measurements of angular size of high- compact radio-sources on
accelerated models based on this large scale modification of gravity. The
predicted age of the Universe in the context of these models is briefly
discussed. We argue that future observations will enable a more accurate test
of these cosmologies and, possibly, show that such models constitute a viable
possibility for the dark energy problem.Comment: 6 pages, 4 figures, to appear in Phys. Rev. D (minor revisions
A modified vaccinia Ankara vaccine expressing spike and nucleocapsid protects rhesus macaques against SARS-CoV-2 Delta infection
SARS-CoV-2 vaccines should induce broadly cross-reactive humoral and T cell responses to protect against emerging variants of concern (VOCs). Here, we inactivated the furin cleavage site (FCS) of spike expressed by a modified vaccinia Ankara (MVA) virus vaccine (MVA/SdFCS) and found that FCS inactivation markedly increased spike binding to human ACE2. After vaccination of mice, the MVA/SdFCS vaccine induced eightfold higher neutralizing antibodies compared with MVA/S, which expressed spike without FCS inactivation, and protected against the Beta variant. We next added nucleocapsid to the MVA/SdFCS vaccine (MVA/SdFCS-N) and tested its immunogenicity and efficacy via intramuscular (IM), buccal (BU), or sublingual (SL) routes in rhesus macaques. IM vaccination induced spike-specific IgG in serum and mucosae (nose, throat, lung, and rectum) that neutralized the homologous (WA-1/2020) and heterologous VOCs, including Delta, with minimal loss (<2-fold) of activity. IM vaccination also induced both spike- and nucleocapsid-specific CD4 and CD8 T cell responses in the blood. In contrast, the SL and BU vaccinations induced less spike-specific IgG in secretions and lower levels of polyfunctional IgG in serum compared with IM vaccination. After challenge with the SARS-CoV-2 Delta variant, the IM route induced robust protection, the BU route induced moderate protection, and the SL route induced no protection. Vaccine-induced neutralizing and non-neutralizing antibody effector functions positively correlated with protection, but only the effector functions correlated with early protection. Thus, IM vaccination with MVA/SdFCS-N vaccine elicited cross-reactive antibody and T cell responses, protecting against heterologous SARS-CoV-2 VOC more effectively than other routes of vaccination
On the Holographic RG-flow and the Low-energy, Strong Coupling, Large N Limit
From the AdS/CFT correspondence, we learn that the classical evolution of
supergravity in the bulk can be reduced to a RG-flow equation for the dual
low-energy, strongly coupled and large N gauge theory on the boundary. This
result has been used to obtain interesting relations between the various terms
in the gravitational part of the boundary effective action, in particular the
term that affect the cosmological constant. It is found that once the
cosmological constant is cancelled in the UV theory, the RG-flow symmetry of
the boundary effective action automatically implies the existence of zero
cosmological constant solutions that extend all the way into the IR. Given the
standard (and well founded) contradiction between the RG-flow idea and the
observational evidence of a small cosmological constant, this is considered to
be an important progress, albeit incomplete, towards the final solution.
Motivated by this success, it would be interesting to see whether this
RG-stability extends outside the scope of strong 't Hooft coupling and large N
regime that are implicitly assumed in the de Boer-Verlinde-Verlinde
Hamilton-Jacobi formulation of the holographic RG-flow equations of the
boundary theory. In this paper, we address this question. Taking into account
the leading order corrections in the 1/N and parameters, we
derive new bulk/boundary relations, from which one can read all the local terms
in the boundary effective action. Next, we use the resulting constraints, to
examine whether the RG-stability of the cosmological constant extends to the
new coupling regime. It would be also interesting to use these constraints to
study the Randall-Sundrum scenario in this case.Comment: 27 pages, LateX, no figures, minor changes, typos corrected and added
more reference
- …