Mon·Feb 15, 2016Monday·February 15, 2016

1. 01*

   BEST sensitivity to O(1) eV sterile neutrino

   Vladislav Barinov🇷🇺 · Vladimir Gavrin🇷🇺 · Dmitry Gorbunov🇷🇺 · Tatiana Ibragimova🇷🇺

   Numerous anomalous results in neutrino oscillation experiments can be attributed to interference of ~1 eV sterile neutrino. The specially designed to fully explore the Gallium anomaly Baksan Experiment on Sterile Transitions (BEST) starts next year. We investigate the sensitivity of BEST in searches for sterile neutrino mixed with electron neutrino. Then, performing the combined analysis of all the Gallium experiments (SAGE, GALLEX, BEST) we find the regions in model parameter space (sterile neutrino mass and mixing angle), which will be excluded if BEST agrees with no sterile neutrino hypothesis. For the opposite case, if BEST observes the signal as it follows from the sterile neutrino explanation of the Gallium (SAGE and GALLEX) anomaly, we show how BEST will improve upon the present estimates of the model parameters.

   hep-phastro-ph.COhep-exPRD(2016)·24 citations
2. 02*

   Improved empirical parametrizations of the ${\gamma }^{\ast }N\to \Delta (1232)$ and ${\gamma }^{\ast }N\to N(1520)$ helicity amplitudes and the Siegert's theorem

   G. Ramalho🇧🇷

   In the nucleon electroexcitation reactions, ${\gamma }^{\ast }N\to R$, where $R$ is a nucleon resonance ($N^{\ast }$), the electric amplitude $E$, and the longitudinal amplitude $S_{1/2}$, are related by $E\propto \frac{\omega }{|\mathbf{q}|}{S}_{1/2}$, at the pseudo-threshold limit ($|\mathbf{q}|\to 0$), where $\omega$ and $|\mathbf{q}|$ are respectively the energy and the magnitude of three-momentum of the photon. The previous relation is usually refereed as the Siegert's theorem. The form of the electric amplitude, defined in terms of the transverse amplitudes $A_{1/2}$ and $A_{3/2}$, and the explicit coefficients of the relation, depend on the angular momentum and parity ($J^P$) of the resonance $R$. The Siegert's theorem is the consequence of the structure of the electromagnetic transition current, which induces constraints between the electromagnetic form factors in the pseudo-threshold limit. In the present work, we study the implications of the Siegert's theorem for the ${\gamma }^{\ast }N\to \Delta (1232)$ and ${\gamma }^{\ast }N\to N(1520)$ transitions. For the ${\gamma }^{\ast }N\to N(1520)$ transition, in addition to the relation between electric amplitude and longitudinal amplitude, we obtain also a relation between the two transverse amplitudes: $A_{1/2}=A_{3/2}/\sqrt{3}$, at the pseudo-threshold. % The constraints at the pseudo-threshold are tested for the MAID2007 parametrizations of the reactions under discussion. New parametrizations for the amplitudes $A_{1/2}$, $A_{3/2}$ and $S_{1/2}$, for the ${\gamma }^{\ast }N\to \Delta (1232)$ and ${\gamma }^{\ast }N\to N(1520)$ transitions, valid for small and large $Q^2$, are proposed. The new parametrizations are consistent with both: the pseudo-threshold constraints (Siegert's theorem) and the empirical data.

   hep-phhep-exnucl-exnucl-thPRD(2016)·30 citations
3. 03*

   Leptogenesis and residual CP symmetry

   Peng Chen🇨🇳 · Gui-Jun Ding🇨🇳 · Stephen F. King🇬🇧

   We discuss flavour dependent leptogenesis in the framework of lepton flavour models based on discrete flavour and CP symmetries applied to the type-I seesaw model. Working in the flavour basis, we analyse the case of two general residual CP symmetries in the neutrino sector, which corresponds to all possible semi-direct models based on a preserved $Z_2$ in the neutrino sector, together with a CP symmetry, which constrains the PMNS matrix up to a single free parameter which may be fixed by the reactor angle. We systematically study and classify this case for all possible residual CP symmetries, and show that the $R$-matrix is tightly constrained up to a single free parameter, with only certain forms being consistent with successful leptogenesis, leading to possible connections between leptogenesis and PMNS parameters. The formalism is completely general in the sense that the two residual CP symmetries could result from any high energy discrete flavour theory which respects any CP symmetry. As a simple example, we apply the formalism to a high energy $S_4$ flavour symmetry with a generalized CP symmetry, broken to two residual CP symmetries in the neutrino sector, recovering familiar results for PMNS predictions, together with new results for flavour dependent leptogenesis.

   hep-phJHEP(2016)·55 citations
4. 04*

   Drell-Yan Constraints on New Electroweak States: LHC as a $pp\to l^{+}{l}^{-}$ Precision Machine

   Christian Gross🇫🇮 · Oleg Lebedev🇫🇮 · Jose Miguel No🇬🇧

   The Standard Model extensions with vector-like states which have either zero hypercharge or zero weak isospin are rather poorly constrained by the electroweak precision measurements. Such new states would however modify the running of the gauge couplings at high energies. As a result, the Drell-Yan process $pp\to l^{+}{l}^{-}$ at the LHC places useful constraints on these models. The relevant observables include both the di-lepton invariant mass distribution $M_{ll}$ and the forward-backward asymmetry $A_{FB}$. We find that the LHC Run 1 data and the initial data from Run 2 surpass the sensitivity of LEP and already put meaningful constraints on the existence of such particles, which will become progressively stronger with more data.

   hep-phMod.Phys.Lett.A(2017)·43 citations
5. 05*

   Naturalness of the relaxion mechanism

   Andrew Fowlie🇦🇺 · Csaba Balazs🇦🇺 · Graham White🇦🇺 · Luca Marzola🇪🇪 · Martti Raidal🇪🇪

   The relaxion mechanism is a novel solution to the hierarchy problem. In this first statistical analysis of the relaxion mechanism, we quantify the relative plausibility of a QCD and a non-QCD relaxion model versus the Standard Model with Bayesian statistics, which includes an automatic penalty for fine-tuning. We find that in light of the hierarchy between the weak and Planck scales, relaxion models are favoured by colossal Bayes-factors. Constraints upon \eg the vacuum energy during relaxation, however, shrink the Bayes-factors such that relaxion models are only slightly favoured. Including the bounds on $\left|{\theta }_{\text{QCD}}\right|$ shatters the plausibility of the QCD relaxion model as it typically yields $\left|{\theta }_{\text{QCD}}\right|\gg 0$. Finally, we augment our models with scalar-field inflation and consider measurements of inflationary observables from BICEP/Planck. We find that, all told, the Standard Model is favoured by huge Bayes-factors as the relaxion models require fine-tuning such that the Hubble parameter is less than the height of the periodic barriers. Thus, whilst we confirm that relaxion models could solve the hierarchy problem, we find that their unconventional cosmology demolishes their plausibility.

   hep-phJHEP(2016)·30 citations
6. 06*

   Hearing the signals of dark sectors with gravitational wave detectors

   Joerg Jaeckel🇩🇪 · Valentin V. Khoze🇬🇧 · Michael Spannowsky🇬🇧

   Motivated by aLIGO's recent discovery of gravitational waves we discuss signatures of new physics that could be seen at ground and space-based interferometers. We show that a first order phase transition in a dark sector would lead to a detectable gravitational wave signal at future experiments, if the phase transition has occurred at temperatures few orders of magnitude higher than the electroweak scale. The source of gravitational waves in this case is associated with the dynamics of expanding and colliding bubbles in the early universe. At the same time we point out that topological defects, such as dark sector domain walls, may generate a detectable signal already at aLIGO. Both -- bubble and domain wall -- scenarios are sourced by semi-classical configurations of a dark new physics sector. In the first case the gravitational wave signal originates from bubble wall collisions and subsequent turbulence in hot plasma in the early universe, while the second case corresponds to domain walls passing through the interferometer at present and is not related to gravitational waves. We find that aLIGO at its current sensitivity can detect smoking-gun signatures from domain wall interactions, while future proposed experiments including the fifth phase of aLIGO at design sensitivity can probe dark sector phase transitions.

   hep-phastro-ph.COastro-ph.HEgr-qc+1PRD(2016)·164 citations
7. 07*

   Magnetized quark matter with a magnetic-field dependent coupling

   Chang-Feng Li🇨🇳 · Li Yang🇨🇳 · Xin-Jian Wen🇨🇳 · Guang-Xiong Peng🇨🇳

   It was recently derived that the QCD running coupling is a function of the magnetic field strength under the strong magnetic field approximation. Inspired by this progress and based on the self-consistent solutions of gap equations, the properties of two-flavor and three-flavor quark matter are studied in the framework of the Nambu-Jona-Lasinio model with a magnetic-field dependent running coupling. We find that the dynamical quark masses as functions of the magnetic field strength are not monotonous in the fully chirally broken phase. Furthermore, the stability of magnetized quark matter with the running coupling is enhanced by lowering the free energy per baryon, which is expected to be more stable than that of the conventional constant coupling case. It is concluded that the magnetized strange quark matter described by running coupling can be absolutely stable.

   hep-phPRD(2016)·27 citations
8. 08*

   Dark Matter Production Associated With a Heavy Quarkonium at B Factories

   Chaehyun Yu🇹🇼 · Tzu-Chiang Yuan🇹🇼

   We investigate light dark matter production associated with a heavy quarkonium at B factories in a model-independent way by adopting the effective field theory approach for the interaction of dark matter with standard model particles. We consider the effective operators for the dark matter-heavy quark interaction, which are relevant to the production of dark matter associated with a heavy quarkonium. We calculate the cross sections for dark matter production associated with a J/psi or eta_c to compare with the standard model backgrounds. We set bounds on the energy scale of new physics for various effective operators and also obtain the corresponding limits for the dark matter-nucleon scattering cross sections for light dark matter with mass of the order of a few GeV.

   hep-phhep-exPLB(2016)·3 citations
9. 09*

   Universal Unitarity Triangle 2016 and the Tension Between $\Delta M_{s,d}$ and ${\epsilon }_K$ in CMFV Models

   Monika Blanke🇩🇪 · Andrzej J. Buras🇩🇪

   Motivated by the recently improved results from the Fermilab Lattice and MILC Collaborations on the hadronic matrix elements entering $\Delta M_{s,d}$ in $B_{s,d}^0-{\bar{B}}_{s,d}^0$ mixing, we determine the Universal Unitarity Triangle (UUT) in models with Constrained Minimal Flavour Violation (CMFV). Of particular importance are the very precise determinations of the ratio $|V_{ub}|/|V_{cb}|=0.0864\pm 0.0025$ and of the angle $\gamma =(63.0\pm 2.1{)}^{\circ }$. They follow in this framework from the experimental values of $\Delta M_d/\Delta M_s$ and of the CP-asymmetry $S_{\psi K_S}$. As in CMFV models the new contributions to meson mixings can be described by a single flavour-universal variable $S(v)$, we next determine the CKM matrix elements $|V_{ts}|$, $|V_{td}|$, $|V_{cb}|$ and $|V_{ub}|$ as functions of $S(v)$ using the experimental value of $\Delta M_s$ as input. The lower bound on $S(v)$ in these models, derived by us in 2006, implies then upper bounds on these four CKM elements and on the CP-violating parameter ${\epsilon }_K$, which turns out to be significantly below its experimental value. This strategy avoids the use of tree-level determinations of $|V_{ub}|$ and $|V_{cb}|$ that are presently subject to considerable uncertainties. On the other hand if ${\epsilon }_K$ is used instead of $\Delta M_s$ as input, $\Delta M_{s,d}$ are found significantly above the data. In this manner we point out that the new lattice data have significantly sharpened the tension between $\Delta M_{s,d}$ and ${\epsilon }_K$ within the CMFV framework. This implies the presence of new physics contributions beyond this framework that are responsible for the breakdown of the flavour universality of the function $S(v)$. We also present the implications of these results for $K^{+}\to {\pi }^{+}\nu \bar{\nu }$, $K_L\to {\pi }^0\nu \bar{\nu }$ and $B_{s,d}\to {\mu }^{+}{\mu }^{-}$ within the Standard Model.

   hep-phhep-exhep-latEPJC(2016)·58 citations
10. 10*

    QED radiative corrections and their impact on H -> tau tau searches at the LHC

    Mieczyslaw Witold Krasny🇫🇷 · Stanislaw Jadach🇵🇱 · Wieslaw Placzek🇵🇱

    In this paper we show that the excess of the tau tau events with respect to the Standard Model background predictions, observed by the ATLAS and CMS collaborations and interpreted as the evidence of the Higgs-boson decay into a pair of tau-leptons, may be accounted for by properly taking into account QED radiative corrections in the modelling of the Z/gamma* -> tau tau background.

    hep-phhep-exEPJC(2016)·1 citation
11. 11*

    DAMA confronts null searches in the effective theory of dark matter-nucleon interactions

    Riccardo Catena🇸🇪 · Alejandro Ibarra🇩🇪 · Sebastian Wild🇩🇪

    We examine the dark matter interpretation of the modulation signal reported by the DAMA experiment from the perspective of effective field theories displaying Galilean invariance. We consider the most general effective coupling leading to the elastic scattering of a dark matter particle with spin 0 or 1/2 off a nucleon, and we analyze the compatibility of the DAMA signal with the null results from other direct detection experiments, as well as with the non-observation of a high energy neutrino flux in the direction of the Sun from dark matter annihilation. To this end, we develop a novel semi-analytical approach for comparing experimental results in the high-dimensional parameter space of the non-relativistic effective theory. Assuming the standard halo model, we find a strong tension between the dark matter interpretation of the DAMA modulation signal and the null result experiments. We also list possible ways-out of this conclusion.

    hep-phastro-ph.COJCAP(2016)·45 citations
12. 12*

    The local renormalization of super-Yang-Mills theories

    Marc Gillioz🇺🇸

    We show how to consistently renormalize $\mathcal{N}=1$ and $\mathcal{N}=2$ super-Yang-Mills theories in flat space with a local (i.e. space-time-dependent) renormalization scale in a holomorphic scheme. The action gets enhanced by a term proportional to derivatives of the holomorphic coupling. In the $\mathcal{N}=2$ case, this new action is exact at all orders in perturbation theory.

    ↳ hep-thhep-phPRD(2016)·3 citations
13. 13*

    Testing Gravity with Gravitational Wave Source Counts

    Erminia Calabrese🇬🇧 · Nicholas Battaglia🇺🇸 · David N. Spergel🇺🇸

    We show that the gravitational wave source counts distribution can test how gravitational radiation propagates on cosmological scales. This test does not require obtaining redshifts for the sources. If the signal-to-noise ratio (SNR, $\rho$) from a gravitational wave source is proportional to the strain then it falls as $R^{-1}$, thus we expect the source counts to follow $dN/d\rho \propto {\rho }^{-4}$. However, if gravitational waves decay as they propagate or propagate into other dimensions, then there can be deviations from this generic prediction. We consider the possibility that the strain falls as $R^{-\gamma }$, where $\gamma =1$ recovers the expected predictions in a Euclidean uniformly-filled universe, and forecast the sensitivity of future observations to deviations from standard General Relativity. We first consider the case of few objects, 7 sources, with a signal-to-noise from 8 to 24, and impose a lower limit on $\gamma$, finding $\gamma >0.33$ at $95\%$ confidence level. The distribution of our simulated sample is very consistent with the distribution of the trigger events reported by Advanced LIGO. Future measurements will improve these constraints: with 100 events, we estimate that $\gamma$ can be measured with an uncertainty of $15\%$. We generalize the formalism to account for a range of chirp masses and the possibility that the signal falls as $\exp (-R/R_0)/R^{\gamma }$.

    ↳ gr-qcastro-ph.COhep-phClass.Quant.Grav.(2016)·34 citations
14. 14*

    Search for Pentaquark Theta+ in Hadronic Reaction at J-PARC

    M. Naruki (for the J-PARC E19 Collaboration)🇯🇵

    A variety of nuclear and hadron physics experiments are being performed using meson beams at the J-PARC Hadron Facility. As the first experiment at the facility, the pentaquark Theta+ was searched for in the pi- p -> K- X reaction with a missing-mass resolution of 2 MeV (FWHM). The number of accumulated beam pions are 7.8x10^10 and 8.1x10^10 for different beam momenta of 1.92 and 2.01 GeV/c, respectively. No significant structure was observed in the missing mass spectra. Upper limits of the production cross section are obtained to be 0.28ub/sr in the laboratory frame at 90% confidence level for each beam momenta. With a help of theoretical models, an upper limit of the total decay width of Theta+ was estimated to be 0.36 and 1.9 MeV for J^P = 1/2+ and 1/2- states, respectively.

    ↳ nucl-exhep-phActa Phys.Polon.B(2016)·3 citations
15. 15*

    Mass Effect on Axial Charge Dynamics

    Er-dong Guo🇨🇳 · Shu Lin🇨🇳

    We studied effect of finite quark mass on the dynamics of axial charge using the D3/D7 model in holography. The mass term in axial anomaly equation affects both the fluctuation (generation) and dissipation of axial charge. We studied the dependence of the effect on quark mass and external magnetic field. For axial charge generation, we calculated the mass diffusion rate, which characterizes the helicity flipping rate. The rate is a non-monotonous function of mass and can be significantly enhanced by the magnetic field. The diffusive behavior is also related to a divergent susceptibility of axial charge. For axial charge dissipation, we found that in the long time limit, the mass term dissipates all the charge effectively generated by parallel electric and magnetic fields. The result is consistent with a relaxation time approximation. The rate of dissipation through mass term is a monotonous increasing function of both quark mass and magnetic field.

    ↳ hep-thhep-phnucl-thPRD(2016)·19 citations
16. 16*

    Light Scalar Mesons in Central Production at COMPASS

    A. Austregesilo (for the COMPASS collaboration)🇩🇪

    COMPASS is a fixed-target experiment at the CERN SPS that studies the spectrum of light-quark hadrons. In 2009, it collected a large dataset using a $190$GeV$/c$ positive hadron beam impinging on a liquid-hydrogen target in order to measure the central exclusive production of light scalar mesons. One of the goals is the search for so-called glueballs, which are hypothetical meson-like objects without valence-quark content. We study the decay of neutral resonances by selecting centrally produced pion pairs from the COMPASS dataset. The angular distributions of the two pseudoscalar mesons are decomposed in terms of partial waves, where particular attention is paid to the inherent mathematical ambiguities. The large dataset allows us to perform a detailed analysis in bins of the two squared four-momentum transfers carried by the exchange particles in the reaction. Possible parameterisations of the mass dependence of the partial-wave amplitudes in terms of resonances are also discussed.

    ↳ hep-exhep-phAIP Conf.Proc.(2016)·9 citations
17. 17*

    A new constraint on millicharged dark matter from galaxy clusters

    Kenji Kadota🇰🇷 · Toyokazu Sekiguchi🇰🇷 · Hiroyuki Tashiro🇯🇵

    We propose a new constraint on millicharged dark matter from considerations on galaxy clusters. The charged dark matter moves under the influence of the randomly oriented magnetic fields in galaxy clusters, and the corresponding dark matter density profile can significantly differ from the concordance CDM predictions which are well supported from the galaxy cluster observations. With a typical amplitude of magnetic fields $B=\mathcal{O}(1)\mu$G and dark matter velocity $v=\mathcal{O}(100)$km/sec at a cluster radius $R\simeq 1$Mpc, we claim that the charge $ϵe$ ($e$ is the elementary charge) of dark matter with mass $m$ should be bounded as $ϵ\lesssim 10^{-14}(m/\mathrm{GeV})$ which is substantially tighter than the other previous constraints.

    ↳ astro-ph.COgr-qchep-ph58 citations
18. 18*

    The pion: an enigma within the Standard Model

    Tanja Horn🇺🇸 · Craig D. Roberts🇺🇸

    Almost 50 years after the discovery of gluons & quarks, we are only just beginning to understand how QCD builds the basic bricks for nuclei: neutrons, protons, and the pions that bind them. QCD is characterised by two emergent phenomena: confinement & dynamical chiral symmetry breaking (DCSB). They are expressed with great force in the character of the pion. In turn, pion properties suggest that confinement & DCSB are closely connected. As both a Nambu-Goldstone boson and a quark-antiquark bound-state, the pion is unique in Nature. Developing an understanding of its properties is thus critical to revealing basic features of the Standard Model. We describe experimental progress in this direction, made using electromagnetic probes, highlighting both improvements in the precision of charged-pion form factor data, achieved in the past decade, and new results on the neutral-pion transition form factor. Both challenge existing notions of pion structure. We also provide a theoretical context for these empirical advances, first explaining how DCSB works to guarantee that the pion is unnaturally light; but also, nevertheless, ensures the pion is key to revealing the mechanisms that generate nearly all the mass of hadrons. Our discussion unifies the charged-pion elastic and neutral-pion transition form factors, and the pion's twist-2 parton distribution amplitude. It also indicates how studies of the charged-kaon form factor can provide significant contributions. Importantly, recent predictions for the large-$Q^2$ behaviour of the pion form factor can be tested by experiments planned at JLab 12. Those experiments will extend precise charged-pion form factor data to momenta that can potentially serve in validating factorisation theorems in QCD, exposing the transition between the nonperturbative and perturbative domains, and thereby reaching a goal that has long driven hadro-particle physics.

    ↳ nucl-thhep-exhep-lathep-ph+1J.Phys.G(2016)·192 citations
19. 19*

    $K\to \pi$ semileptonic form factors with $N_f=2+1+1$ Twisted Mass fermions

    N. Carrasco🇮🇹 · P. Lami🇮🇹 · V. Lubicz🇮🇹 · L. Riggio🇮🇹 · S. Simula🇮🇹 · C. Tarantino🇮🇹

    We present a lattice QCD determination of the vector and scalar form factors of the semileptonic $K\to \pi \ell \nu$ decay which are relevant for the extraction of the CKM matrix element $|V_{us}|$ from experimental data. Our results are based on the gauge configurations produced by the European Twisted Mass Collaboration with $N_f=2+1+1$ dynamical fermions, which include in the sea, besides two light mass degenerate quarks, also the strange and the charm quarks. We use data simulated at three different values of the lattice spacing and with pion masses as small as $210$ MeV. Our final result for the vector form factor at zero momentum transfer is $f_{+}(0)=0.9709(46)$, where the uncertainty is both statistical and systematic combined in quadrature. Using the latest experimental value of $f_{+}(0)|V_{us}|$ from $K_{\ell 3}$ decays, we obtain $|V_{us}|=0.2230(11)$, which allows to test the unitarity constraint of the Standard Model below the permille level once the determination of $|V_{ud}|$ from superallowed nuclear $\beta$ decays is adopted. A slight tension with unitarity at the level of $\sim 2$ standard deviations is observed. Moreover we present our results for the semileptonic scalar $f_0(q^2)$ and vector $f_{+}(q^2)$ form factors in the whole range of values of the squared four-momentum transfer $q^2$ measured in $K_{\ell 3}$ decays, obtaining a very good agreement with the momentum dependence of the experimental data. We provide a set of synthetic data points representing our results for the vector and scalar form factors at the physical point for several selected values of $q^2$.

    ↳ hep-lathep-exhep-phPRD(2016)·132 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.