119228618
New primordial-magnetic-field limit from the latest LIGO S5 data
Since the energy momentum tensor of a magnetic field always contains a spin-2 component in its anisotropic stress, stochastic primordial magnetic field (PMF) in the early universe must generate stochastic gravitational-wave (GW) background. This process will greatly affect the relic gravitational wave (RGW), which is one of the major scientific goals of the laser interferometer GW detections. Recently, the fifth science (S5) run of laser interferometer gravitational-wave observatory (LIGO) gave a latest upper limit Omega(GW) < 6.9 x 10(-6) on the RGW background. Utilizing this upper limit, we derive new PMF limits: for a scale of galactic cluster lambda = 1 Mpc, the amplitude of PMF, that produced by the electroweak phase transition, has to be weaker than B(lambda) <= 4 x 10(-7) G; for a scale of supercluster lambda = 100 Mpc, the amplitude of PMF has to be weaker than B(lambda) <= 9 x 10(-11) G. In this manner, GW observation has potential to make interesting contributions to the study of primordial magnetic field.
62836920
Dark energy and fate of the Universe
AbstractWe explore the ultimate fate of the Universe by using a divergence-free parametrization for dark energy w(z)=w0+wa [ln(2 + z) / (1 + z) − ln 2]. Unlike the Chevallier-Polarski-Linder parametrization, this parametrization has well behaved, bounded behavior for both high redshifts and negative redshifts, and thus can genuinely cover many theoretical dark energy models. After constraining the parameter space of this parametrization by using the current cosmological observations, we find that, at the 95.4% confidence level, our Universe can still exist at least 16.7 Gyr before it ends in a big rip. Moreover, for the phantom energy dominated Universe, we find that a gravitationally bound system will be destroyed at a time $${{t \simeq P\sqrt {2\left| {1 + 3w( - 1)} \right|} } \mathord{\left/
 {\vphantom {{t \simeq P\sqrt {2\left| {1 + 3w( - 1)} \right|} } {\left[ {6\pi \left| {1 + w( - 1)} \right|} \right]}}} \right.
 \kern-\nulldelimiterspace} {\left[ {6\pi \left| {1 + w( - 1)} \right|} \right]}}$$, where P is the period of a circular orbit around this system, before the big rip.
119188783
Probing interaction and spatial curvature in the holographic dark energy model
In this paper we place observational constraints on the interaction and spatial curvature in the holographic dark energy model. We consider three kinds of phenomenological interactions between holographic dark energy and matter, i.e., the interaction term Q is proportional to the energy densities of dark energy (rho(A)), matter (p(m)), and matter plus dark energy (p(m) + p(A)). For probing the interaction and spatial curvature in the holographic dark energy model, we use the latest observational data including the type la supernovae (SNIa) Constitution data, the shift parameter of the cosmic microwave background (CMB) given by the five-year Wilkinson Microwave Anisotropy Probe (WMAP5) observations, and the baryon acoustic oscillation (BAO) measurement, from the Sloan Digital Sky Survey (SDSS). Our results show that, the interaction and spatial curvature in the holographic dark energy model are both rather small. Besides, it is interesting to find that there exists significant degeneracy between the phenomenological interaction and the spatial curvature in the holographic dark energy model.
119118433
Holographic dark energy models: a comparison from the latest observational data
The holographic principle of quantum gravity theory has been applied to the dark energy (DE) problem, and so far three holographic DE models have been proposed: the original holographic dark energy (HDE) model, the agegraphic dark energy (ADE) model, and the holographic Ricci dark energy (RDE) model. In this work, we perform the best-fit analysis on these three models, by using the latest observational data including the Union+CFA3 sample of 397 Type Ia supernovae (SNIa), the shift parameter of the cosmic microwave background (CMB) given by the five-year Wilkinson Microwave Anisotropy Probe (WMAP5) observations, and the baryon acoustic oscillation (BAO) measurement from the Sloan Digital Sky Survey (SDSS). The analysis shows that for HDE, chi(2)(min) = 465.912; for RDE, chi(2)(min) = 483.130; for ADE, chi(2)(min) = 481.694. Among these models, HDE model can give the smallest. chi(2)(min). Besides, we also use the Bayesian evidence (BE) as a model selection criterion to make a comparison. It is found that for HDE, ADE, and RDE, Delta ln BE = -0.86, -5.17, and -8.14, respectively. So, it seems that the HDE model is more favored by the observational data.
119224877
Cosmic Age Test in Inhomogeneous Cosmological Models Mimicking $\Lambda$CDM on the Light-Cone
The possibility of reconstructing a spherically symmetric inhomogeneous Lemaitre-Tolman-Bondi (LTB) model with Lambda CDM observations has drawn much attention. Recently, an inhomogeneous LTB model having the same luminosity-distance and light-cone mass density of the homogeneous Lambda CDM model was reconstructed. From the Wilkinson microwave anisotropy probe 7-year measurements together with other cosmological observations, we calculate the cosmic age at our position in this LTB model, and obtain a constraint t(LTB) < 11.7 Gyr at 1 sigma confidence level. We find that this result is, although 2 Gyr younger compared with the age of the homogeneous Lambda CDM model, still within 1 sigma agreement with the constraint of cosmic age given by current astronomical measurements. We expect that in the future, with the help of more advanced observations, we can distinguish the reconstructed inhomogeneous LTB model from the homogeneous Lambda CDM model.
118416982
Testing modified gravity models with recent cosmological observations
We explore the cosmological implications of five modified gravity (MG) models by using the recent cosmological observational data, including the recently released SNLS3 type Ia supernovae sample, the cosmic microwave background anisotropy data from the Wilkinson Microwave Anisotropy Probe 7-yr observations, the baryon acoustic oscillation results from the Sloan Digital Sky Survey data release 7, and the latest Hubble constant measurement utilizing the Wide Field Camera 3 on the Hubble Space Telescope. The MG models considered include the Dvali-Gabadadze-Porrati (DGP) model, two f (R) models, and two f (T) models. We find that compared with the ΛCDM model, MG models can not lead to an appreciable reduction of the χmin2. The analysis of AIC and BIC shows that the simplest cosmological constant model (ΛCDM) is still the most preferred by the current data, and the DGP model is strongly disfavored. In addition, from the observational constraints, we also reconstruct the evolutions of the growth factor in these models. We find that the current available growth factor data are not enough to distinguish these MG models from the ΛCDM model.
202105722
Search for strong gravity signatures in same-sign dimuon final states using the ATLAS detector at the LHC
A search for microscopic black holes has been performed in a same-sign dimuon final state using 1.3 fb(-1) of proton-proton collision data collected with the ATLAS detector at a centre of mass energy of 7 TeV at the CERN Large Hadron Collider. The data are found to be consistent with the expectation from the Standard Model and the results are used to derive exclusion contours in the context of a low scale gravity model.
122255934
PROTON BRANCH OF MODIFIED URCA PROCESS IN STRONG MAGNETIC FIELD AND SUPERFLUIDITY OF NEUTRON STAR CORES
The modified URCA process produces efficient neutrino energy losses in neutron star cores, and has been shown to go via neutron and proton branches. Based on the improved electron chemical potential and critical temperature of superfluidity, the effects of strong magnetic field and superfluidity on the proton branch of modified URCA process are investigated simultaneously in this paper. The results show that strong magnetic field enhances the neutrino emissivities compared to the case in zero magnetic field, and superfluidity reduces the emissivities significantly. For the total neutrino emissivities, the magnetic field is dominant at the initial stage of neutron star cooling, but the superfluidity becomes crucial as the temperature drops below the critical temperature.
113400995
Vorticity and magnetic field production in relativistic ideal fluids
In the framework of relativistic ideal hydrodynamics, we study the production mechanism for vorticity and magnetic field in relativistic ideal fluids. It is demonstrated that in the uncharged fluids the thermal vorticity will always satisfy the Kelvin's theorem and the circulation must be conserved. However, in the charged fluids, the vorticity and magnetic field can be produced by the interaction between the entropy gradients and the fluid velocity gradients. Especially, in the multiple charged fluids, the vorticity and magnetic field can be produced by the interaction between the inhomogeneous charge density ratio and the fluid velocity gradients even if the entropy distribution is homogeneous, which provides another mechanism for the production of vorticity and magnetic field in relativistic plasmas or in the early universe.
18284543
Measurement of the top pair production cross section in the lepton+jets channel using a jet flavor discriminant
We present a new method to measure the top quark pair production cross section and the background rates with data corresponding to an integrated luminosity of 2.7  fb-1 from pp collisions at √s=1.96  TeV collected with the CDF II Detector. We select events with a single electron or muon candidate, missing transverse energy, and at least one b-tagged jet. We perform a simultaneous fit to a jet flavor discriminant across nine samples defined by the number of jets and b tags. An advantage of this approach is that many systematic uncertainties are measured in situ and inversely scale with integrated luminosity. We measure a top cross section of σtt =7.64±0.57(stat+syst)±0.45(luminosity)  pb.
109931583
The experimental study on beam-photoelectron instability in BEPC
A vertical coupled bunch instability explained as the photoelectron instability (PEI) was observed in the photon factory at KEK. To further investigate the instability, the experiments on the PEI have been carried out in Beijing Electron Positron Collider (BEPC) with the collaboration between MEP, China and KEK, Japan. Many interesting phenomena have been observed for different sets of parameters.