1,381 research outputs found
First order thermal phase transition with 126 GeV Higgs mass
We study the strength of the electroweak phase transition in models with two
light Higgs doublets and a light SU(3)_c triplet by means of lattice
simulations in a dimensionally reduced effective theory. In the parameter
region considered the transition on the lattice is significantly stronger than
indicated by a 2-loop perturbative analysis. Within some ultraviolet
uncertainties, the finding applies to MSSM with a Higgs mass m_h approximately
126 GeV and shows that the parameter region useful for electroweak baryogenesis
is enlarged. In particular (even though only dedicated analyses can quantify
the issue), the tension between LHC constraints after the 7 TeV and 8 TeV runs
and frameworks where the electroweak phase transition is driven by light stops,
seems to be relaxed.Comment: Presented at 31st International Symposium on Lattice Field Theory -
LATTICE 201
Testing the accuracy of reflection-based supermassive black hole spin measurements in AGN
X-ray reflection is a very powerful method to assess the spin of supermassive
black holes (SMBHs) in active galactic nuclei (AGN), yet this technique is not
universally accepted. Indeed, complex reprocessing (absorption, scattering) of
the intrinsic spectra along the line of sight can mimic the relativistic
effects on which the spin measure is based. In this work, we test the
reliability of SMBH spin measurements that can currently be achieved through
the simulations of high-quality XMM-Newton and NuSTAR spectra. Each member of
our group simulated ten spectra with multiple components that are typically
seen in AGN, such as warm and (partial-covering) neutral absorbers,
relativistic and distant reflection, and thermal emission. The resulting
spectra were blindly analysed by the other two members. Out of the 60 fits, 42
turn out to be physically accurate when compared to the input model. The SMBH
spin is retrieved with success in 31 cases, some of which (9) are even found
among formally inaccurate fits (although with looser constraints). We show
that, at the high signal-to-noise ratio assumed in our simulations, neither the
complexity of the multi-layer, partial-covering absorber nor the input value of
the spin are the major drivers of our results. The height of the X-ray source
(in a lamp-post geometry) instead plays a crucial role in recovering the spin.
In particular, a success rate of 16 out of 16 is found among the accurate fits
for a dimensionless spin parameter larger than 0.8 and a lamp-post height lower
than five gravitational radii.Comment: 20 pages, 9 figures, 4 tables. Accepted for publication in A&
An Examination of the Spectral Variability in NGC 1365 with Suzaku
We present jointly analyzed data from three deep Suzaku observations of NGC
1365. These high signal-to-noise spectra enable us to examine the nature of
this variable, obscured AGN in unprecedented detail on timescales ranging from
hours to years. We find that, in addition to the power-law continuum and
absorption from ionized gas seen in most AGN, inner disk reflection and
variable absorption from neutral gas within the Broad Emission Line Region are
both necessary components in all three observations. We confirm the clumpy
nature of the cold absorbing gas, though we note that occultations of the inner
disk and corona are much more pronounced in the high-flux state (2008) than in
the low-flux state (2010) of the source. The onset and duration of the "dips"
in the X-ray light curve in 2010 are both significantly longer than in 2008,
however, indicating that either the distance to the gas from the black hole is
larger, or that the nature of the gas has changed between epochs. We also note
significant variations in the power-law flux over timescales similar to the
cold absorber, both within and between the three observations. The warm
absorber does not vary significantly within observations, but does show
variations in column density of a factor of more than 10 on timescales less
than 2 weeks that seem unrelated to the changes in the continuum, reflection or
cold absorber. By assuming a uniform iron abundance for the reflection and
absorption, we have also established that an iron abundance of roughly 3.5
times the solar value is sufficient to model the broad-band spectrum without
invoking an additional partial-covering absorber. Such a measurement is
consistent with previous published constraints from the 2008 Suzaku observation
alone, and with results from other Seyfert AGN in the literature.Comment: 19 pages, 11 figures, accepted for publication in MNRA
A scalable data-plane architecture for one-to-one device-to-device communications in LTE-Advanced
One-to-one device-to-device (D2D) communications are expected to play a major role in future releases of LTE-A, as well as in future 5G networks. Despite the abundance of works on resource allocation for D2D communications, few works, if any, discuss how D2D should be realized within the LTE-A protocol stack. While it is generally understood that D2D endpoints should be able to communicate both on the direct path or sidelink (SL) and on the relayed path (RP) through the eNB, little has been said on how this can be achieved in practice. In this paper we present a comprehensive proposal for a data-plane architecture for D2D communication: we define how communications should occur on the SL and the RP, and propose a solution for the challenges associated with mode switching between the SL and the RP. In particular, we argue that two different communication modes on the RP are required to allow D2D connections to be kept alive across cell borders in a multicell environment. Our proposal is scalable, since it does not require any signaling, and is guaranteed to not introduce losses. We evaluate our proposal through detailed system-level simulations, also focusing on its interplay with transport-layer protocols
Gravitational Backreaction Effects on the Holographic Phase Transition
We study radion stabilization in the compact Randall-Sundrum model by
introducing a bulk scalar field, as in the Goldberger and Wise mechanism, but
(partially) taking into account the backreactions from the scalar field on the
metric. Our generalization reconciles the radion potential found by Goldberger
and Wise with the radion mass obtained with the so-called superpotential method
where backreaction is fully considered. Moreover we study the holographic phase
transition and its gravitational wave signals in this model. The improved
control over backreactions opens up a large region in parameter space and
leads, compared to former analysis, to weaker constraints on the rank N of the
dual gauge theory. We conclude that, in the regime where the 1/N expansion is
justified, the gravitational wave signal is detectable by LISA.Comment: 42 pages, 4 figures; v2: minor changes for the publicatio
Clinical significance of epithelial-to-mesenchymal transition in laryngeal carcinoma: Its role in the different subsites
Background: During epithelial-to-mesenchymal transition, cancer cells lose adhesion capacity gaining migratory properties. The role of the process on prognosis has been evaluated in 50 cases of laryngeal carcinoma. Methods: E-cadherin, N-cadherin, β-catenin, α-catenin, γ-catenin, caveolin-1, and vimentin immunohistochemical expression were evaluated using a double score based on staining intensity and cellular localization. Results: Cytoplasmic E-cadherin and α/γ catenin staining were associated with a decrease in survival, cytoplasmic β-catenin was associated with advanced stage, and N-cadherin and vimentin expression were associated with poor differentiation and tumor relapse. On the basis of cancer cells, epithelial or mesenchymal morphological and immunophenotypic similarity we identified 4 main subgroups correlated with a transition to a more undifferentiated phenotype, which have a different pattern of relapse and survival. Conclusion: The negative prognostic role of epithelial-to-mesenchymal transition has been confirmed and a predictive role in glottic tumors has been suggested, leading us to propose epithelial-to-mesenchymal transition as an additional adverse feature in laryngeal carcinoma
Luminosity Functions of Gamma-Ray Burst Afterglows
Aims: Use the standard fireball model to create virtual populations of
gamma-ray burst afterglows and study their luminosity functions.
Methods: We randomly vary the parameters of the standard fireball model to
create virtual populations of afterglows. We use the luminosity of each burst
at an observer's time of 1 day to create a luminosity function and compare our
results with available observational data to assess the internal consistency of
the standard fireball model.
Results: We show that the luminosity functions can be described by a function
similar to a log normal distribution with an exponential cutoff. The function
parameters are frequency dependent but not very dependent on the model
parameter distributions used to create the virtual populations. Comparison with
observations shows that while there is good general agreement with the data, it
is difficult to explain simultaneously the X-ray and optical data. Possible
reasons for this are discussed and the most likely one is that the standard
fireball model is incomplete and that decoupling of the X-ray and optical
emission mechanism may be needed.Comment: 5 pages, 4 figures; accepted for publication in A&
Pearson cross-correlation in the first four black hole binary mergers
We adopt the Pearson cross-correlation measure to analyze the LIGO Hanford and LIGO Livingston detector data streams around the events GW150914, GW151012,GW151226 and GW170104. We find that the Pearson cross-correlation method is sensitive to these signals, with correlations peaking when the black hole binaries reconstructed by the LIGO Scientific and Virgo Collaborations, are merging. We compare the obtained cross-correlations with the statistical correlation fluctuations arising in simulated Gaussian noise data and in LIGO data at times when no event is claimed. Our results for the significance of the observed cross-correlations are broadly consistent with those announced by the LIGO Scientific and Virgo Collaborations based on matched-filter analysis. In the same data, if we subtract the maximum likelihood waveforms corresponding to the announced signals, no residual cross-correlations persists at a statistically significant level
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