DSpace Collection:
http://hdl.handle.net/2445/19703
2019-04-20T08:25:43Z
2019-04-20T08:25:43Z
Detection of persistent VHE gamma-ray emission from PKS 1510-089 by the MAGIC telescopes during low states between 2012 and 2017
Galindo Fernández, Daniel
Paredes i Poy, Josep Maria
Ribó Gomis, Marc
Torres Albà, Núria
Molina, Edgar
MAGIC Collaboration
http://hdl.handle.net/2445/131925
2019-04-09T21:11:22Z
2019-04-09T12:44:28Z
Title: Detection of persistent VHE gamma-ray emission from PKS 1510-089 by the MAGIC telescopes during low states between 2012 and 2017
Author: Galindo Fernández, Daniel; Paredes i Poy, Josep Maria; Ribó Gomis, Marc; Torres Albà, Núria; Molina, Edgar; MAGIC Collaboration
Abstract: PKS 1510-089 is a flat spectrum radio quasar strongly variable in the optical and GeV range. To date, very high-energy (VHE, > 100 GeV) emission has been observed from this source either during long high states of optical and GeV activity or during short flares. Aims. We search for low-state VHE gamma-ray emission from PKS 1510-089. We characterize and model the source in a broadband context, which would provide a baseline over which high states and flares could be better understood. Methods. PKS 1510-089 has been monitored by the MAGIC telescopes since 2012. We use daily binned Fermi-LAT flux measurements of PKS 1510-089 to characterize the GeV emission and select the observation periods of MAGIC during low state of activity. For the selected times we compute the average radio, IR, optical, UV, X-ray, and gamma-ray emission to construct a low-state spectral energy distribution of the source. The broadband emission is modeled within an external Compton scenario with a stationary emission region through which plasma and magnetic fields are flowing. We also perform the emission-model-independent calculations of the maximum absorption in the broad line region (BLR) using two different models. Results. The MAGIC telescopes collected 75 hr of data during times when the Fermi-LAT flux measured above 1 GeV was below 3? × 10 -8 ? cm -2 ? s -1 , which is the threshold adopted for the definition of a low gamma-ray activity state. The data show a strongly significant (9.5¿) VHE gamma-ray emission at the level of (4.27 ± 0.61 stat ) × 10 -12 ? cm -2 ? s -1 above 150 GeV, a factor of 80 lower than the highest flare observed so far from this object. Despite the lower flux, the spectral shape is consistent with earlier detections in the VHE band. The broadband emission is compatible with the external Compton scenario assuming a large emission region located beyond the BLR. For the first time the gamma-ray data allow us to place a limit on the location of the emission region during a low gamma-ray state of a FSRQ. For the used model of the BLR, the 95% confidence level on the location of the emission region allows us to place it at a distance > 74% of the outer radius of the BLR. © ESO 2018.
2019-04-09T12:44:28Z
I=2 ππ S-wave scattering phase shift from lattice QCD
Beane, Silas R.
Chang, Emmanuel
Detmold, William
Lin, H. W.
Luu, Thomas C.
Orginos, Kostas
Parreño García, Assumpta
Savage, Martin J.
Torok, Aaron
Walker-Loud, André
NPLQCD Collaboration
http://hdl.handle.net/2445/131769
2019-04-08T21:10:19Z
2019-04-08T11:15:54Z
Title: I=2 ππ S-wave scattering phase shift from lattice QCD
Author: Beane, Silas R.; Chang, Emmanuel; Detmold, William; Lin, H. W.; Luu, Thomas C.; Orginos, Kostas; Parreño García, Assumpta; Savage, Martin J.; Torok, Aaron; Walker-Loud, André; NPLQCD Collaboration
Abstract: The π + π + s -wave scattering phase shift is determined below the inelastic threshold using lattice QCD. Calculations were performed at a pion mass of m π ∼ 390 MeV with an anisotropic n f = 2 + 1 clover fermion discretization in four lattice volumes, with spatial extent L ∼ 2.0 , 2.5, 3.0 and 3.9 fm, and with a lattice spacing of b s ∼ 0.123 fm in the spatial direction and b t ∼ b s / 3.5 in the time direction. The phase shift is determined from the energy eigenvalues of π + π + systems with both zero and nonzero total momentum in the lattice volume using Lüscher's method. Our calculations are precise enough to allow for a determination of the threshold scattering parameters, the scattering length a , the effective range r , and the shape parameter P , in this channel and to examine the prediction of two-flavor chiral perturbation theory: m 2 π a r = 3 + O ( m 2 π / Λ 2 χ ) . Chiral perturbation theory is used, with the lattice QCD results as input, to predict the scattering phase shift (and threshold parameters) at the physical pion mass. Our results are consistent with determinations from the Roy equations and with the existing experimental phase shift data.
2019-04-08T11:15:54Z
Gravitational waves in the presence of a cosmological constant
Bernabeu, José
Espriu, D. (Domènec)
Puigdomènech, Daniel
http://hdl.handle.net/2445/131768
2019-04-08T21:09:05Z
2019-04-08T11:14:24Z
Title: Gravitational waves in the presence of a cosmological constant
Author: Bernabeu, José; Espriu, D. (Domènec); Puigdomènech, Daniel
Abstract: We derive the effects of a nonzero cosmological constant Λ on gravitational wave propagation in the linearized approximation of general relativity. In this approximation, we consider the situation where the metric can be written as g μ ν = η μ ν + h Λ μ ν + h W μ ν , h Λ , W μ ν ≪ 1 , where h Λ μ ν is the background perturbation and h W μ ν is a modification interpretable as a gravitational wave. For Λ ≠ 0 , this linearization of Einstein equations is self-consistent only in certain coordinate systems. The cosmological Friedmann-Robertson-Walker coordinates do not belong to this class and the derived linearized solutions have to be reinterpreted in a coordinate system that is homogeneous and isotropic to make contact with observations. Plane waves in the linear theory acquire modifications of order √ Λ , both in the amplitude and the phase, when considered in Friedmann-Robertson-Walker coordinates. In the linearization process for h μ ν , we have also included terms of order O ( Λ h μ ν ) . For the background perturbation h Λ μ ν , the difference is very small, but when the term h W μ ν Λ is retained the equations of motion can be interpreted as describing massive spin-2 particles. However, the extra degrees of freedom can be approximately gauged away, coupling to matter sources with a strength proportional to the cosmological constant itself. Finally, we discuss the viability of detecting the modifications caused by the cosmological constant on the amplitude and phase of gravitational waves. In some cases, the distortion with respect to gravitational waves propagating in Minkowski space-time is considerable. The effect of Λ could have a detectable impact on pulsar timing arrays.
2019-04-08T11:14:24Z
Search for CP violation in D+→K−K+π+ decays
Calvo Gómez, M.
Camboni, Alessandro
Enterria i Adan, David G. d'
Garrido Beltrán, Lluís
Grabalosa Gándara, Marc
Graciani Díaz, Ricardo
Graugés Pous, Eugeni
López Asamar, E.
Musy, Marco
Pérez-Calero Yzquierdo, Antonio
Pie Valls, B. (Blai)
Potterat, Cédric
Puig Navarro, Albert
Ruiz, Hugo (Ruiz Pérez)
Vázquez Gómez, R.
Vilasis-Cardona, Xavier
LHCb Collaboration
http://hdl.handle.net/2445/131767
2019-04-08T21:10:18Z
2019-04-08T11:12:03Z
Title: Search for CP violation in D+→K−K+π+ decays
Author: Calvo Gómez, M.; Camboni, Alessandro; Enterria i Adan, David G. d'; Garrido Beltrán, Lluís; Grabalosa Gándara, Marc; Graciani Díaz, Ricardo; Graugés Pous, Eugeni; López Asamar, E.; Musy, Marco; Pérez-Calero Yzquierdo, Antonio; Pie Valls, B. (Blai); Potterat, Cédric; Puig Navarro, Albert; Ruiz, Hugo (Ruiz Pérez); Vázquez Gómez, R.; Vilasis-Cardona, Xavier; LHCb Collaboration
Abstract: A model-independent search for direct C P violation in the Cabibbo-suppressed decay D + → K − K + π + in a sample of approximately 370 000 decays is carried out. The data were collected by the LHCb experiment in 2010 and correspond to an integrated luminosity of 35 pb − 1 . The normalized Dalitz plot distributions for D + and D − are compared using four different binning schemes that are sensitive to different manifestations of C P violation. No evidence for C P asymmetry is found.
2019-04-08T11:12:03Z
Non-relativistic bound states in a moving thermal bath
Escobedo, Miguel Angel
Mannarelli, Massimo
Soto Riera, Joan
http://hdl.handle.net/2445/131766
2019-04-08T21:09:04Z
2019-04-08T11:10:28Z
Title: Non-relativistic bound states in a moving thermal bath
Author: Escobedo, Miguel Angel; Mannarelli, Massimo; Soto Riera, Joan
Abstract: We study the propagation of nonrelativistic bound states moving at constant velocity across a homogeneous thermal bath and we develop the effective field theory which is relevant in various dynamical regimes. We consider values of the velocity of the bound state ranging from moderate to highly relativistic and temperatures at all relevant scales smaller than the mass of the particles that form the bound state. In particular, we consider two distinct temperature regimes, corresponding to temperatures smaller or higher than the typical momentum transfer in the bound state. For temperatures smaller or of the order of the typical momentum transfer, we restrict our analysis to the simplest system, a hydrogenlike atom. We build the effective theory for this system first considering moderate values of the velocity and then the relativistic case. For large values of the velocity of the bound state, the separation of scales is such that the corresponding effective theory resembles the soft collinear effective theory (SCET). For temperatures larger than the typical momentum transfer we also consider muonic hydrogen propagating in a plasma which contains photons and massless electrons and positrons, so that the system resembles very much a heavy quarkonium in a thermal medium of deconfined quarks and gluons. We study the behavior of the real and imaginary part of the static two-body potential, for various velocities of the bound state, in the hard thermal loop approximation. We find that Landau damping ceases to be the relevant mechanism for dissociation from a certain critical velocity on, in favor of screening. Our results are relevant for understanding how the properties of heavy quarkonia states produced in the initial fusion of partons in the relativistic collision of heavy ions are affected by the presence of an equilibrated quark-gluon plasma.
2019-04-08T11:10:28Z
Gravitational lensing effects on the baryonic acoustic oscillation signature in the redshift-space correlation function
Yoo, Jaiyul
Miralda Escudé, Jordi
http://hdl.handle.net/2445/131764
2019-04-08T21:09:03Z
2019-04-08T11:09:06Z
Title: Gravitational lensing effects on the baryonic acoustic oscillation signature in the redshift-space correlation function
Author: Yoo, Jaiyul; Miralda Escudé, Jordi
Abstract: Measurements of the baryonic acoustic oscillation (BAO) peak in the redshift-space correlation function yield the angular diameter distance D A ( z ) and the Hubble parameter H ( z ) as a function of redshift, constraining the properties of dark energy and space curvature. We discuss the perturbations introduced in the galaxy correlation function by gravitational lensing through the effect of magnification bias and its cross correlation with the galaxy density. At the BAO scale, gravitational lensing adds a small and slowly varying component to the galaxy correlation function and does not change its shape significantly, through which the BAO peak is measured. The relative shift in the position of the BAO peak caused by gravitational lensing in the angle-averaged correlation function is 10 − 4 at z = 1 , rising to 10 − 3 at z = 2.5 . Lensing effects are stronger near the line of sight; however, the relative peak shift increases only to 10 − 3.3 and 10 − 2.4 at z = 1 and z = 2.5 , when the galaxy correlation is averaged within 5 degrees of the line of sight (containing only 0.4% of the galaxy pairs in a survey). Furthermore, the lensing contribution can be measured separately and subtracted from the observed correlation at the BAO scale.
2019-04-08T11:09:06Z
Too big, too early? Multiple high-redshift galaxy clusters: implications
Hoyle, Ben
Jiménez, Raúl (Jiménez Tellado)
Verde, Licia
http://hdl.handle.net/2445/131763
2019-04-08T21:10:17Z
2019-04-08T11:06:02Z
Title: Too big, too early? Multiple high-redshift galaxy clusters: implications
Author: Hoyle, Ben; Jiménez, Raúl (Jiménez Tellado); Verde, Licia
Abstract: To date, 14 high-redshift ( z > 1.0 ) galaxy clusters with mass measurements have been observed, spectroscopically confirmed, and are reported in the literature. These objects should be exceedingly rare in the standard Λ cold dark matter ( Λ CDM ) model. We conservatively approximate the selection functions of these clusters' parent surveys and quantify the tension between the abundances of massive clusters as predicted by the standard Λ CDM model and the observed ones. We alleviate the tension, considering non-Gaussian primordial perturbations of the local type, characterized by the parameter f NL , and derive constraints on f NL arising from the mere existence of these clusters. At the 95 % confidence level, f NL > 467 , with cosmological parameters fixed to their most likely WMAP5 values, or f NL ≳ 123 (at 95 % confidence) if we marginalize over prior WMAP5 parameters. In combination with f NL constraints from cosmic microwave background and halo bias, this determination implies a scale dependence of f NL at ≃ 3 σ . Given the assumptions made in the analysis, we expect any future improvements to the modeling of the non-Gaussian mass function, survey volumes, or selection functions to increase the significance of f NL > 0 found here. In order to reconcile these massive, high- z clusters with f NL = 0 , their masses would need to be systematically lowered by 1.5 σ , or the σ 8 parameter should be ∼ 3 σ higher than cosmic microwave background (and large-scale structure) constraints. The existence of these objects is a puzzle: it either represents a challenge to the Λ CDM paradigm or it is an indication that the mass estimates of clusters are dramatically more uncertain than we think.
2019-04-08T11:06:02Z
Implications for primordial non-Gaussianity (fNL) from weak lensing masses of high-z galaxy clusters
Jiménez, Raúl (Jiménez Tellado)
Verde, Licia
http://hdl.handle.net/2445/131762
2019-04-08T21:09:02Z
2019-04-08T11:04:51Z
Title: Implications for primordial non-Gaussianity (fNL) from weak lensing masses of high-z galaxy clusters
Author: Jiménez, Raúl (Jiménez Tellado); Verde, Licia
Abstract: The recent weak-lensing measurement of the dark matter mass of the high-redshift galaxy cluster XMMUJ2235.3-2557 of ( 8.5 ± 1.7 ) × 10 14 M ⊙ at z = 1.4 , indicates that, if the cluster is assumed to be the result of the collapse of dark matter in a primordial Gaussian field in the standard lambda cold dark matter model, then its abundance should be < 2 × 10 − 3 clusters in the observed area. Here we investigate how to boost the probability of XMMUJ2235.3-2557, in particular, resorting to deviations from Gaussian initial conditions. We show that this abundance can be boosted by factors > 3 - 10 if the non-Gaussianity parameter f local NL is in the range 150-200. This value is comparable to the limit for f NL obtained by current constraints from the cosmic microwave background. We conclude that mass determination of high-redshift, massive clusters can offer a complementary probe of primordial non-Gaussianity.
2019-04-08T11:04:51Z
Non-Gaussianity and the CMB bispectrum: Confusion between primordial and lensing-Rees-Sciama contribution?
Mangilli, Anna
Verde, Licia
http://hdl.handle.net/2445/131761
2019-04-08T21:10:16Z
2019-04-08T11:02:21Z
Title: Non-Gaussianity and the CMB bispectrum: Confusion between primordial and lensing-Rees-Sciama contribution?
Author: Mangilli, Anna; Verde, Licia
Abstract: We revisit the predictions for the expected cosmic microwave background bispectrum signal from the cross-correlation of the primary-lensing-Rees-Sciama signal; we point out that it can be a significant contaminant to the bispectrum signal from primordial non-Gaussianity of the local type. This non-Gaussianity, usually parametrized by the non-Gaussian parameter f N L , arises, for example, in multifield inflation. In particular both signals are frequency-independent, and are maximized for nearly squeezed configurations. While their detailed scale-dependence and harmonic imprints are different for generic bispectrum shapes, we show that, if not included in the modeling, the primary-lensing-Rees-Sciama contribution yields an effective f N L of 10 when using a bispectrum estimator optimized for local non-Gaussianity. Considering that expected 1 − σ errors on f N L are < 10 from forthcoming experiments, we conclude that the contribution from this signal must be included in future constraints on f N L from the cosmic microwave background bispectrum.
2019-04-08T11:02:21Z
Graviton production in the scaling of a long-cosmic-string network
Kleidis, Kostas
Kuiroukidis, Apostolos
Papadopoulos, Demetrios B.
Verdaguer, Enric
http://hdl.handle.net/2445/131760
2019-04-08T21:09:01Z
2019-04-08T10:57:40Z
Title: Graviton production in the scaling of a long-cosmic-string network
Author: Kleidis, Kostas; Kuiroukidis, Apostolos; Papadopoulos, Demetrios B.; Verdaguer, Enric
Abstract: In a previous paper [K. Kleidis, D. B. Papadopoulos, E. Verdaguer, and L. Vlahos, Phys. Rev. D 78, 024027 (2008).] we considered the possibility that (within the early-radiation epoch) there has been (also) a short period of a significant presence of cosmic strings. During this radiation-plus-strings stage the Universe matter-energy content can be modeled by a two-component fluid, consisting of radiation (dominant) and a cosmic-string fluid (subdominant). It was found that, during this stage, the cosmological gravitational waves that had been produced in an earlier (inflationary) epoch with comoving wave numbers below a critical value (which depends on the physics of the cosmic-string network) were filtered, leading to a distorsion in the expected (scale-invariant) cosmological gravitational wave power spectrum. In any case, the cosmological evolution gradually results in the scaling of any long-cosmic-string network and, hence, after a short time interval, the Universe enters into the late-radiation era. However, along the transition from an early-radiation epoch to the late-radiation era through the radiation-plus-strings stage, the time dependence of the cosmological scale factor is modified, something that leads to a discontinuous change of the corresponding scalar curvature, which, in turn, triggers the quantum-mechanical creation of gravitons. In this paper we discuss several aspects of such a process, and, in particular, the observational consequences on the expected gravitational-wave power spectrum.
2019-04-08T10:57:40Z