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Andrea Soddu

Publications and source records attributed to Andrea Soddu.

12 recordsLinked to original sources
arXiv2017

A Principal component analysis of the diffuse interstellar bands

We present a principal component analysis of 23 line of sight parameters (including the strengths of 16 diffuse interstellar bands, DIBs) for a well-chosen sample of single-cloud sightlines representing a broad range of environmental conditions. Our analysis indicates that the majority ($\sim$93\%) of the variations in the measurements can be captured by only four parameters The main driver (i.e., the first principal component) is the amount of DIB-producing material in the line of sight, a quantity that is extremely well traced by the equivalent width of the $λ$5797 DIB. The second principal component is the amount of UV radiation, which correlates well with the $λ$5797/$λ$5780 DIB strength ratio. The remaining two principal components are more difficult to interpret, but are likely related to the properties of dust in the line of sight (e.g., the gas-to-dust ratio). With our PCA results, the DIBs can then be used to estimate these line of sight parameters.

astro-ph.GA↗
arXiv2014

Cerebral functional connectivity periodically (de)synchronizes with anatomical constraints

This paper studies the link between resting-state functional connectivity (FC), measured by the correlations of the fMRI BOLD time courses, and structural connectivity (SC), estimated through fiber tractography. Instead of a static analysis based on the correlation between SC and the FC averaged over the entire fMRI time series, we propose a dynamic analysis, based on the time evolution of the correlation between SC and a suitably windowed FC. Assessing the statistical significance of the time series against random phase permutations, our data show a pronounced peak of significance for time window widths around 20-30 TR (40-60 sec). Using the appropriate window width, we show that FC patterns oscillate between phases of high modularity, primarily shaped by anatomy, and phases of low modularity, primarily shaped by inter-network connectivity. Building upon recent results in dynamic FC, this emphasizes the potential role of SC as a transitory architecture between different highly connected resting state FC patterns. Finally, we show that networks implied in consciousness-related processes, such as the default mode network (DMN), contribute more to these brain-level fluctuations compared to other networks, such as the motor or somatosensory networks. This suggests that the fluctuations between FC and SC are capturing mind-wandering effects.

q-bio.NC↗
arXiv2007

Large Time-dependent CP Violation in B_s^0 System and Finite D^0-D^0bar Mass Difference in Four Generation Standard Mode

Combining the measured B_s mixing with b \to s\ell^+\ell^- rate data, we find a sizable 4 generation t' quark effect is allowed, for example with m_{t'} \sim 300 GeV and V_{t's}^*V_{t'b} \sim 0.025 e^{\pm i 70^\circ}, which could underly the new physics indications in CP violation studies of b \to s qbar q transitions. With positive phase, large and negative mixing-dependent CP violation in B_s system is predicted, \sin 2Φ_{B_s} \sim -0.5 to -0.7. This can also be probed via width difference methods. As a corollary, the short distance generated D^0-D^0bar mass difference is found to be consistent with, if not slightly higher than, recent B factory measurements, while CP violation is subdued with \sin 2Φ_D \sim -0.2.

hep-ph↗
arXiv2006

eV Seesaw with Four Generations

We extend the eV seesaw scenario to four lepton generations. The LSND anomaly is taken as the right-handed seesaw scale, i.e. m_R ~ eV. The fourth generation then gives a heavy pseudo-Dirac neutrino which largely decouples from other generations, and is relatively stable. One effectively has a 3+3 solution to the LSND anomaly, where we illustrate with numerical solutions. Our study indicates that the third mixing angle sin^2(theta13) is likely less than 0.01.

hep-ph↗
arXiv2006

Direct CP Violation in B+ to J/psi K+ Decay as Probe for New Physics

Currently there are New Physics hints in mixing-induced CP violation S(phi K0), S(pi0 K0) < S(J/psi K0), unequal direct CP violation A(K+ pi-) differs A(K+ pi0), and maybe even in measured S(J/psi K0) vs prediction from global fit to other data. However, these hints either suffer from experimental uncertainties, or uncertain hadronic corrections, and are not yet unequivocal. Motivated by these hints, however, we point out that a unique probe may be direct CP violation in B to JψK mode. An asymmetry observed at 1% or higher would indicate New Physics.

hep-ph↗
arXiv2006

Four Generation CP Violation in B -> phi K^0, pi^0 K^0, eta' K^0 and Hadronic Uncertainties

The fourth generation can give the correct trend of S_{phi K^0}, S_{pi^0 K^0} < sin2phi_1/beta, as indicated by data, and the effect, being largely leading order, is robust against hadronic uncertainties. The effect on S_{eta' K^0}, however, is diluted away by hadronic effects, and S_{eta' K^0} \simeq sin2phi_1/beta is expected. The near maximal arg[V^*_{t's}V_{t'b}] \lesssim 90^\circ that is needed could resolve the unequal direct CP violation seen in B -> K^+ pi^- and K^+ pi^0 modes, and is consistent with b ->s l^+l^- and B_s mixing constraints.

hep-ph↗
arXiv2005

Baryon Number Violation Involving Higher Generations

Proton stability seems to constrain rather strongly any baryon number violating process. We investigate the possibility of baryon number violating processes involving right-handed dynamics or higher generation quarks. Our results strongly suggest that there will be no possibility to observe baryon number violation in tau or higher generation quark decays, at any future machine.

hep-ph↗
arXiv2005

Enhanced KL to pi0 nu nubar from Direct CP Violation in B to K pi with Four Generations

Recent CP violation results in B decays suggest that Z penguins may have large weak phase. This can be realized by the four generation (standard) model. Concurrently, B to Xs l+ l- and Bs mixing allow for sizable Vt's* Vt'b only if it is nearly imaginary. Such large effects in b to s transitions would affect s to d transitions, as kaon constraints would demand Vt'd different from zero. Using Gamma(Z to b bbar) to bound |Vt'b|, we infer sizable |Vt's| < |Vt'b| < |Vus|$. Imposing epsilon_K, K+ to pi+ nu nubar and epsilon'/epsilon constraints, we find Vt'd* Vt's = few x 10^(-4) with large phase, enhancing KL to pi0 nu nubar to 5x10^(-10) or even higher. Interestingly, Delta_mBd and sin(2PhiBd) are not much affected, as |Vt'd* Vt'b| << |Vtd* Vtb| = 0.01.

hep-ph↗
arXiv2005

Difference in B^+ and B^0 Direct CP Asymmetry as Effect of a Fourth Generation

Direct CP violation in B^0-> K^+π^- decay has emerged at -10% level, but the asymmetry in B^+ -> K^+π^0 mode is consistent with zero. This difference points towards possible New Physics in the electroweak penguin operator. We point out that a sequential fourth generation, with sizable V^*_{t's}V_{t'b} and near maximal phase, could be a natural cause. We use the perturbative QCD factorization approach for B-> Kπamplitudes. While the B^0-> K^+π^- mode is insensitive to t', we critically compare t' effects on direct CP violation in B^+ -> K^+π^0 with b-> s\ell^+\ell^- and B_s mixing. If the K^+π^0-K^+π^- asymmetry difference persists, we predict \sin2Φ_{B_s} to be negative.

hep-ph↗
arXiv2004

B->J/psi K* in a Supersymmetric Right-handed Flavor Mixing Scenario

A supersymmetric extension of the Standard Model, with maximal s_R-b_R mixing and a new source of CP violation, contains all the necessary ingredients to account for a possible anomaly in the measured CP asymmetry in B->phi K_s decay. In the same framework we study the decay B->J/psi K*, paying particular attention to observables that can be extracted by performing a time dependent angular analysis, and become nonzero because of new physics effects.

hep-ph↗
arXiv2001

Rare K decays in a model of quark and lepton masses

An extension of a model of neutrino masses to the quark sector provides an interesting link between these two sectors. A parameter which is important to describe neutrino oscillations and masses is found to be a crucial one appearing in various ``penguin'' operators, in particular the so-called Z penguin. This parameter is severely constrained by the rare decay process $K_{L} \to μ^{+} μ^{-}$. This in turn has interesting implications on the decay rates of other rare processes such as $K_{L} \to μe$, etc..., as well as on the masses of the neutrinos and the masses of the vector-like quarks and leptons which appear in our model.

hep-ph↗