Neutrinoless double beta decay in effective field theory: the light Majorana neutrino exchange mechanism

We present the first chiral effective theory derivation of the neutrinoless double beta-decay $nn\rightarrow pp$ potential induced by light Majorana neutrino exchange. The effective-field-theory framework has allowed us to identify and parameterize short- and long-range contributions previously missed in the literature. These contributions can not be absorbed into parameterizations of the single nucleon form factors. Starting from the quark and gluon level, we perform the matching onto chiral effective field theory and subsequently onto the nuclear potential. To derive the nuclear potential mediating neutrinoless double beta-decay, the hard, soft and potential neutrino modes must be integrated out. This is performed through next-to-next-to-leading order in the chiral power counting, in both the Weinberg and pionless schemes. At next-to-next-to-leading order, the amplitude receives additional contributions from the exchange of ultrasoft neutrinos, which can be expressed in terms of nuclear matrix elements of the weak current and excitation energies of the intermediate nucleus. These quantities also control the two-neutrino double beta-decay amplitude. Finally, we outline strategies to determine the low-energy constants that appear in the potentials, by relating them to electromagnetic couplings and/or by matching to lattice QCD calculations.Comment: 20 pages, 6 figure

Exceptional flaring activity of the anomalous X-ray pulsar 1E 1547.0-5408

(Abridged) We studied an exceptional period of activity of the anomalous X-ray pulsar 1E 1547.0-5408 in January 2009, during which about 200 bursts were detected by INTEGRAL. The major activity episode happened when the source was outside the field of view of all the INTEGRAL instruments. But we were still able to study the properties of 84 bursts detected simultaneously by the anti-coincidence shield of the spectrometer SPI and by the detector of the imager ISGRI. We find that the luminosity of the 22 January 2009 bursts of 1E 1547.0-5408 was > 1e42 erg/s. This luminosity is comparable to that of the bursts of soft gamma repeaters (SGR) and is at least two orders of magnitude larger than the luminosity of the previously reported bursts from AXPs. Similarly to the SGR bursts, the brightest bursts of 1E 1547.0-5408 consist of a short spike of ~100 ms duration with a hard spectrum, followed by a softer extended tail of 1-10 s duration, which occasionally exhibits pulsations with the source spin period of ~2 s. The observation of AXP bursts with luminosities comparable to the one of SGR bursts strengthens the conjecture that AXPs and SGRs are different representatives of one and the same source type.Comment: 9 pages, 10 figures, accepted to Astronomy & Astrophysic

Right-handed charged currents in the era of the Large Hadron Collider

We discuss the phenomenology of right-handed charged currents in the framework of the Standard Model Effective Field Theory, in which they arise due to a single gauge-invariant dimension-six operator. We study the manifestations of the nine complex couplings of the $W$ to right-handed quarks in collider physics, flavor physics, and low-energy precision measurements. We first obtain constraints on the couplings under the assumption that the right-handed operator is the dominant correction to the Standard Model at observable energies. We subsequently study the impact of degeneracies with other Beyond-the-Standard-Model effective interactions and identify observables, both at colliders and low-energy experiments, that would uniquely point to right-handed charged currents.Comment: 50 pages plus appendices and reference

Optical and near-infrared photometric monitoring of the transient X-ray binary A0538-66 with REM

The transient Be/X-ray binary A0538-66 shows peculiar X-ray and optical variability. Despite numerous studies, the intrinsic properties underlying its anomalous behaviour remain poorly understood. Since 2014 September we are conducting the first quasi-simultaneous optical and near-infrared photometric monitoring of A0538-66 in seven filters with the Rapid Eye Mount (REM) telescope, aiming to understand the properties of this binary system. We found that the REM lightcurves show fast flares lasting one or two days that repeat almost regularly every ~16.6 days, the orbital period of the neutron star. If the optical flares are powered by X-ray outbursts through photon reprocessing, the REM lightcurves indicate that A0538-66 is still active in X-rays: bright X-ray flares (L_x > 1E37 erg/s) could be observable during the periastron passages. The REM lightcurves show a long-term variability that is especially pronounced in the g band and decreases with increasing wavelength, until it no longer appears in the near-infrared lightcurves. In addition, A0538-66 is fainter with respect to previous optical observations most likely due to the higher absorption of the stellar radiation of a denser circumstellar disc. On the basis of the current models, we interpret these observational results with a circumstellar disc around the Be star observed nearly edge-on during a partial depletion phase. The REM lightcurves also show short-term variability on timescales of ~1 day possibly indicative of perturbations in the density distribution of the circumstellar disc caused by the tidal interaction with the neutron star.Comment: Accepted for publication in Astronomy & Astrophysic

Neutrinoless double beta decay in chiral effective field theory: lepton number violation at dimension seven

We analyze neutrinoless double beta decay ($0\nu\beta\beta$) within the framework of the Standard Model Effective Field Theory. Apart from the dimension-five Weinberg operator, the first contributions appear at dimension seven. We classify the operators and evolve them to the electroweak scale, where we match them to effective dimension-six, -seven, and -nine operators. In the next step, after renormalization group evolution to the QCD scale, we construct the chiral Lagrangian arising from these operators. We develop a power-counting scheme and derive the two-nucleon $0\nu\beta\beta$ currents up to leading order in the power counting for each lepton-number-violating operator. We argue that the leading-order contribution to the decay rate depends on a relatively small number of nuclear matrix elements. We test our power counting by comparing nuclear matrix elements obtained by various methods and by different groups. We find that the power counting works well for nuclear matrix elements calculated from a specific method, while, as in the case of light Majorana neutrino exchange, the overall magnitude of the matrix elements can differ by factors of two to three between methods. We calculate the constraints that can be set on dimension-seven lepton-number-violating operators from $0\nu\beta\beta$ experiments and study the interplay between dimension-five and -seven operators, discussing how dimension-seven contributions affect the interpretation of $0\nu\beta\beta$ in terms of the effective Majorana mass $m_{\beta \beta}$.Comment: Matches version published in JHE

Infrared and X-ray variability of the transient Anomalous X-ray Pulsar XTE J1810-197

We report on observations aimed at searching for flux variations from the proposed IR counterpart of the Anomalous X-ray Pulsar XTE J1810-197. These data, obtained in March 2004 with the adaptive optics camera NAOS-CONICA at the ESO VLT, show that the candidate proposed by Israel et al. (2004) was fainter by Delta H=0.7+/-0.2 and Delta Ks=0.5+/-0.1 with respect to October 2003, confirming it as the IR counterpart of XTE J1810-197. We also report on an XMM-Newton observation carried out the day before the VLT observations. The 0.5-10 keV absorbed flux of the source was 2.2x10^-11 erg/s/cm^2, which is less by a factor of about two compared to the previous XMM-Newton observation on September 2003. Therefore, we conclude that a similar flux decrease took place in the X-ray and IR bands. We briefly discuss these results in the framework of the proposed mechanism(s) responsible for the IR variable emission of Anomalous X-ray Pulsars.Comment: accepted by A&A Letter

Properties and observability of glitches and anti-glitches in accreting pulsars

Several glitches have been observed in young, isolated radio pulsars, while a clear detection in accretion-powered X-ray pulsars is still lacking. We use the Pizzochero snowplow model for pulsar glitches as well as starquake models to determine for the first time the expected properties of glitches in accreting pulsars and their observability. Since some accreting pulsars show accretion-induced long-term spin-up, we also investigate the possibility that anti-glitches occur in these stars. We find that glitches caused by quakes in a slow accreting neutron star are very rare and their detection extremely unlikely. On the contrary, glitches and anti-glitches caused by a transfer of angular momentum between the superfluid neutron vortices and the non-superfluid component may take place in accreting pulsars more often. We calculate the maximum jump in angular velocity of an anti-glitch and we find that it is expected to be about 1E-5 - 1E-4 rad/s. We also note that since accreting pulsars usually have rotational angular velocities lower than those of isolated glitching pulsars, both glitches and anti-glitches are expected to have long rise and recovery timescales compared to isolated glitching pulsars, with glitches and anti-glitches appearing as a simple step in angular velocity. Among accreting pulsars, we find that GX 1+4 is the best candidate for the detection of glitches with currently operating X-ray instruments and future missions such as the proposed Large Observatory for X-ray Timing (LOFT).Comment: Accepted for publication in Astronomy & Astrophysics. 6 pages. Minor changes to match the final A&A versio