Fri·Dec 9, 2016Friday·December 9, 2016

1. 01*

   Muon g-2 in GMSB with Adjoint Messengers

   Ilia Gogoladze🇺🇸 · Cem Salih Un🇹🇷

   We explored the sparticle mass spectrum in light of the muon g-2 anomaly and the little hierarchy problem in a class of gauge mediated supersymmetry breaking model. Here the messenger fields transform in the adjoint representation of the Standard Model gauge symmetry. To avoid unacceptably light right-handed slepton masses the standard model is supplemented by additional U(1)_B-L gauge symmetry. Considering a non-zero U(1)_B-L D-term leads to an additional contribution to the soft supersymmetry breaking mass terms which makes the right-handed slepton masses compatible with the current experimental bounds. We show that in the framework of Lambda_{3}<0 and mu < 0, the muon g-2 anomaly and the observed 125 GeV Higgs boson mass a can be simultaneously accommodated. The slepton masses in this case are predicted to lie in the few hundred GeV range, which can be tested at LHC. Despite the heavy colored spectrum the the little hierarchy problem in this model can be ameliorated and electroweak fine tuning parameter can be as low as 10 or so.

   hep-phPRD(2017)·7 citations
2. 02*

   Unblinding the Dark Matter Blind Spots

   Tao Han🇺🇸 · Felix Kling🇺🇸 · Shufang Su🇺🇸 · Yongcheng Wu🇨🇳

   The dark matter (DM) blind spots in the Minimal Supersymmetric Standard Model (MSSM) refer to the parameter regions where the couplings of the DM particles to the $Z$-boson or the Higgs boson are almost zero, leading to vanishingly small signals for the DM direct detections. In this paper, we carry out comprehensive analyses for the DM searches under the blind-spot scenarios in MSSM. Guided by the requirement of acceptable DM relic abundance, we explore the complementary coverage for the theory parameters at the LHC, the projection for the future underground DM direct searches, and the indirect searches from the relic DM annihilation into photons and neutrinos. We find that (i) the spin-independent (SI) blind spots may be rescued by the spin-dependent (SD) direct detection in the future underground experiments, and possibly by the indirect DM detections from IceCube and SuperK neutrino experiments; (ii) the detection of gamma rays from Fermi-LAT may not reach the desirable sensitivity for searching for the DM blind-spot regions; (iii) the SUSY searches at the LHC will substantially extend the discovery region for the blind-spot parameters. The dark matter blind spots thus may be unblinded with the collective efforts in future DM searches.

   hep-phJHEP(2017)·53 citations
3. 03*

   Hunting the Gluon Orbital Angular Momentum at the Electron-Ion Collider

   Xiangdong Ji🇨🇳 · Feng Yuan🇺🇸 · Yong Zhao🇺🇸

   Applying the connection between the parton Wigner distribution and orbital angular momentum (OAM), we investigate the probe of the gluon OAM in hard scattering processes at the planned electron-ion collider. We show that the single longitudinal target-spin asymmetry in the hard diffractive dijet production is very sensitive to the gluon OAM distribution. The associated spin asymmetry leads to a characteristic azimuthal angular correlation of $\sin ({\varphi }_q-{\varphi }_{\Delta })$, where ${\varphi }_{\Delta }$ and ${\varphi }_q$ are the azimuthal angles of the proton momentum transfer and the relative transverse momentum between the quark-antiquark pair. This study will enable a first measurement of the gluon OAM in the proton spin sum rule.

   hep-phhep-exnucl-exnucl-thPRL(2017)·76 citations
4. 04*

   Gluon orbital angular momentum at small-$x$

   Yoshitaka Hatta🇯🇵 · Yuya Nakagawa🇯🇵 · Bowen Xiao🇨🇳 · Feng Yuan🇺🇸 · Yong Zhao🇺🇸

   We present a general analysis of the orbital angular momentum (OAM) distribution of gluons $L_g(x)$ inside the nucleon with particular emphasis on the small-$x$ region. We derive a novel operator representation of $L_g(x)$ in terms of Wilson lines and argue that it is approximately proportional to the gluon helicity distribution $L_g(x)\approx -2\Delta G(x)$ at small-$x$. We also compute longitudinal single spin asymmetry in exclusive diffractive dijet production in lepton-nucleon scattering in the next-to-eikonal approximation and show that the asymmetry is a direct probe of the gluon helicity/OAM distribution as well as the QCD odderon exchange.

   hep-phhep-exnucl-exnucl-thPRD(2017)·129 citations
5. 05*

   Cosmological evolution of Yukawa couplings: the 5D perspective

   Benedict von Harling🇩🇪 · Geraldine Servant🇩🇪

   The cosmological evolution of standard model Yukawa couplings may have major implications for baryogenesis. In particular, as highlighted recently, the CKM matrix alone could be the source of CP-violation during electroweak baryogenesis provided that the Yukawa couplings were large and varied during the electroweak phase transition. We provide a natural realisation of this idea in the context of Randall-Sundrum models and show that the geometrical warped approach to the fermion mass hierarchy may naturally display the desired cosmological dynamics. The key ingredient is the coupling of the Goldberger-Wise scalar, responsible for the IR brane stabilisation, to the bulk fermions, which modifies the fermionic profiles. This also helps alleviating the usually tight constraints from CP-violation in Randall-Sundrum scenarios. We study how the Yukawa couplings vary during the stabilisation of the Randall-Sundrum geometry and can thus induce large CP-violation during the electroweak phase transition. Using holography, we discuss the 4D interpretation of this dynamical interplay between flavour and electroweak symmetry breaking.

   hep-phJHEP(2017)·32 citations
6. 06*

   Affleck-Dine Leptogenesis with Varying Peccei-Quinn Scale

   Kyu Jung Bae🇰🇷 · Howard Baer🇺🇸 · Koichi Hamaguchi🇯🇵 · Kazunori Nakayama🇯🇵

   The Affleck-Dine leptogenesis scenario along the LHu flat direction is reconsidered. It is known that successful Affleck-Dine leptogenesis requires that the lightest neutrino mass is extremely small. This situation can be significantly relaxed if the neutrino mass in the early universe is different from the present one. We consider a supersymmetric Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) type model, which provides a solution to the strong CP problem and generates a SUSY mu-term and right-handed neutrino masses. If the PQ scale during lepton number generation is much larger than the present value, leptogenesis is very efficient so that enough baryon number can be generated without introducing a hierarchically small neutrino mass. The final baryon asymmetry is related to the mu-term, and hence linked to the level of electroweak fine-tuning. We also show the PQ breaking scalar dynamics that keeps a large PQ breaking scale during inflation and lepton number generation. The mu-term generating superpotential plays an important role for preserving the lepton asymmetry during saxion oscillation. In this scenario, the axion isocurvature perturbation is naturally suppressed.

   hep-phJHEP(2017)·6 citations
7. 07*

   Study of the rare decays $B_{s,d}^{\ast }\to {\mu }^{+}{\mu }^{-}$

   Suchismita Sahoo🇮🇳 · Rukmani Mohanta🇮🇳

   We investigate the effect of scalar leptoquarks and family non-universal $Z^{\prime }$ boson on the rare leptonic decays of $B_{s,d}^{\ast }$ mesons, mediated by the FCNC transitions $b\to (d,s)l^{+}{l}^{-}$. They are sensitive to a variety of new physics operators as opposed to the $B_{s,d}$ leptonic modes and hence, can provide an ideal testing ground to look for new physics beyond the standard model. We work out the constraint on new physics parameter space using the measured branching ratios of $B_{d,s}\to {\mu }^{+}{\mu }^{-}$ processes and the $B_q-{\bar{B}}_q$ mixing data. Using the constrained parameters we estimate the branching ratios of $B_{d,s}\to {\mu }^{+}{\mu }^{-}(e^{+}{e}^{-})$ processes. We find that the branching ratios are reasonably enhanced from their corresponding standard model values in the $X(3,2,1/6)$ leptoquark model and are expected to be within the reach of Run II/III of LHC experiments.

   hep-phJ.Phys.G(2017)·19 citations
8. 08*

   Finite nuclei in the reggeon "toy" model

   M.A. Braun🇷🇺

   Hadron-nucleus amplitudes at high energies are studied in the "toy" Regge model in zero transverse dimension for finite nuclei, when the standard series of fan diagrams is converted into a finite sum and looses physical sense at quite low energies. Taking into account all the loop contributions by numerical methods we find a physically meaningful amplitudes at all energies. They practically coincide with the amplitudes for infinite nuclei. A surprizing result is that for finite nuclei and small enough triple pomeron coupling the infinite series of fan diagrams describes the amplitude quite well in spite of the fact that in reality the series should be cut and as such deprived of any physical sense at high energies.

   hep-phEPJC(2017)·6 citations
9. 09*

   Overall momentum balance and redistribution of the lost energy in asymmetric dijet events in 2.76~ATeV Pb-Pb collisions with a multi-phase transport model

   Zhan Gao🇨🇳 · Ao Luo🇨🇳 · Guo-Liang Ma🇨🇳 · Guang-You Qin🇨🇳 · Han-Zhong Zhang🇨🇳

   The overall transverse momentum balance and the redistribution of the lost energy from hard jets for asymmetric dijet events in PbPb collisions at 2.76~ATeV at the LHC is studied within A Multi-Phase Transport (AMPT) model. A detailed analysis is performed for the projected transverse momentum $⟨\text{slashed}{p}_T^{||}⟩$ contributed from the final charged hadrons carrying different transverse momenta and emitted from different angular directions. We find that the transverse momentum projection $⟨\text{slashed}{p}_T^{||}⟩$ in the leading jet direction is mainly contributed by hard hadrons ($p_T>8.0$~GeV/$c$) in both peripheral and central PbPb collisions, while the opposite direction in central collisions is dominated by soft hadrons ($p_T=0.5$-$2.0$~GeV/$c$). The study of in-cone and out-of-cone contributions to $⟨\text{slashed}{p}_T^{||}⟩$ shows that these soft hadrons are mostly emitted at large angles away from the dijet axis. Our AMPT calculation is in qualitative agreement with the CMS measurements and the primary mechanism for the energy transported to large angles in the AMPT model is the elastic scattering at the partonic stage. Future studies including also inelastic processes should be helpful in understanding the overestimation of the magnitudes of in-cone and out-of-cone imbalances from our AMPT calculations, and shed light on different roles played by radiative and collisional processes in the redistribution of the lost energy from hard jets.

   hep-phPRC(2018)·24 citations
10. 10*

    Quark Mass Matrices, textures and CKM precision measurements

    Rohit Verma🇮🇳

    In the light of several recent analyses pointing towards texture 4-zero Fritzsch-like quark mass matrices as the only viable structures for quark mass matrices, this work adopts a model independent approach to reconstruct an alternate and simplified structure of texture specific quark mass matrices in a generalized 'u-diagonal' basis within the Standard Model framework using the Unitarity of CKM matrix and the observed hierarchies in quark mass spectra and mixing angles. It is observed that the measured 1$\sigma$ values of the three physical parameters namely $m_{\mathrm{u}}$, $m_{\mathrm{d}}$ and $s_{12}$ naturally lead to the vanishing of (11) element in the down type quark mass matrix and that the single measurable CP violating phase ${\delta }_{13}$ in the CKM matrix is sufficient enough in $M_{\mathrm{d}}^{\prime }$ to explain the observed mixing pattern in a suitable basis. The leading order as well as exact analytic phenomenological solutions are addressed for the modest pattern of quark mass matrices derived from CKM matrix and precision measurements of mixing parameters.

    hep-phInt.J.Mod.Phys.A(2017)·2 citations
11. 11*

    Faddeev fixed center approximation to $\pi \bar{K}{K}^{\ast }$ system and the ${\pi }_1(1600)$

    Xu Zhang🇨🇳 · Ju-Jun Xie🇨🇳 · Xurong Chen🇨🇳

    We investigate the three-body system of $\pi \bar{K}{K}^{\ast }$ by using the fixed-center approximation to the Faddeev equation, taking the interaction between $\pi$ and $\bar{K}$, $\pi$ and $K^{\ast }$, and $\bar{K}$ and $K^{\ast }$ from the chiral unitary approach. The study is made assuming scattering of a $\pi$ on a $\bar{K}{K}^{\ast }$ cluster, which is known to generate the $f_1(1285)$ state. The resonant structure around $1650$ MeV shows up in the modulus squared of the $\pi$-$(\bar{K}{K}^{\ast }{)}_{f_1(1285)}$ scattering amplitude and suggests that a $\pi$-$(\bar{K}{K}^{\ast }{)}_{f_1(1285)}$ state, with "exotic" quantum numbers $J^{PC}=1^{-+}$, can be formed. This state can be identified as the observed ${\pi }_1(1600)$ resonance. We suggest that this is the origin of the present ${\pi }_1(1600)$ resonance and propose to look at the $\pi f_1(1285)$ mode in future experiments to clarify the issue.

    hep-phhep-exnucl-exnucl-thPRD(2017)·7 citations
12. 12*

    Influence of confining gluon configurations on the $P\to {\gamma }^{\ast }\gamma$ transition form factors

    Sergei N. Nedelko🇷🇺 · Vladimir E. Voronin🇷🇺

    Transition form factors $F_{P{\gamma }^{\ast }{\gamma }^{(\ast )}}$ of pseudoscalar mesons are studied within the framework of the domain model of confinement, chiral symmetry breaking and hadronization. In this model, the QCD vacuum is described by the statistical ensemble of domain wall networks which represents the almost everywhere homogeneous Abelian (anti-)self-dual gluon field configurations. Calculations of the form factors are performed consistently with mass spectra of light, heavy-light and double-heavy mesons, their weak and strong decay constants. Influence of the nonperturbative intermediate range gluon fields on asymptotic behaviour of pion transition form factor is of particular interest, as it can potentially lead to the growth of $Q^2{F}_{\pi {\gamma }^{\ast }\gamma }(Q^2)$. It is found that $Q^2{F}_{\pi {\gamma }^{\ast }\gamma }(Q^2)$ approaches a constant value at asymptotically large $Q^2$. However, this limit differs from the standard factorization bound, though for pion form factor complies with Belle data more likely than with BaBar ones. At the same time the generally accepted factorization bound is shown to be satisfied for the case of the symmetric kinematics, $Q^2{F}_{P{\gamma }^{\ast }{\gamma }^{\ast }}(Q^2)$. Peculiarities of description of $\eta$, ${\eta }^{\prime }$ and ${\eta }_c$ form factors within the model are discussed in detail.

    hep-phPRD(2017)·14 citations
13. 13*

    SU(3) flavor symmetry breaking in large $N_c$ excited hyperons

    Fl. Stancu🇧🇪

    The $1/N_c$ expansion method for studying the mass spectrum of excited baryons is shortly reviewed together with applications to mixed symmetric states. The $[70,{\mathbf{\ell }}^{+}]$ multiplet, belonging to the $N$ = 2 band, is reanalyzed, with emphasis on hyperons and the SU(3) symmetry breaking operators entering the mass formula to first order. An important result is that the hierarchy of masses as a function of strangeness is correctly reproduced for all multiplets. Predictions for unknown excited hyperons to SU(6) $\times$ O(3) multiplets are made.

    hep-phPRD(2016)·1 citation
14. 14*

    Dark Matter, Leptogenesis, and Neutrino Mass in the Minimal Extension of the SM with $U(1{)}_{B-L}\otimes Z_2$

    Wei-Min Yang🇨🇳

    I suggest a minimal extension of the SM with $U(1{)}_{B-L}\otimes Z_2$. It can simultaneously accommodate the tiny neutrino mass, cold dark mater and baryon asymmetry besides the SM. All of the new physics arise from the $U(1{)}_{B-L}$ violation at the energy scale about 1000 TeV. The model can naturally explain the "WIMP Miracle" and elegantly achieve the leptogenesis, in addition, some predictions of the model are possible and promising to be tested in near future experiments.

    hep-ph0 citations
15. 15*

    QCD Vacuum as Domain Wall Network

    Sergei N. Nedelko🇷🇺 · Vladimir E. Voronin🇷🇺

    Domain model of confinement, chiral symmetry breaking and hadronization is based on description of QCD vacuum gluon configurations as an ensemble of almost everywhere homogeneous Abelian (anti-)self-dual fields. The ensemble can be explicitly constructed as domain wall network. We shortly overview this approach and within this framework discuss the effects of QCD vacuum polarization by strong electromagnetic fields. It is stressed that such polarization effects can play the role of trigger for deconfinement.

    hep-ph1 citation
16. 16*

    Pion transition form factor in the Domain model of QCD vacuum

    Sergei Nedelko🇷🇺 · Vladimir Voronin🇷🇺

    Domain model of QCD allows for description of wide range of meson observables, dynamical chiral symmetry breaking, and resolution of $U_A(1)$ and strong $CP$ problems. The purpose of the present study is transition form-factor of neutral pseudoscalar mesons, and how they are influenced by the typical vacuum configurations of the model -- almost everywhere homogeneous Abelian (anti-)self-dual fields. Asymptotic behavior of the calculated pion form-factor supports Belle trend, but the asymptotic value of $Q^2{F}_{\pi {\gamma }^{\ast }\gamma }$ differs from the prediction of factorization theorems.

    hep-phEPJ Web Conf.(2017)·0 citations
17. 17*

    Difference between two species of emu hides a test for lepton flavour violation

    Christopher Gorham Lester🇬🇧 · Benjamin Hylton Brunt🇬🇧

    We argue that an LHC measurement of some simple quantities related to the ratio of rates of e+mu- to e-mu+ events is surprisingly sensitive to as-yet unexcluded R-parity violating supersymmetric models with non-zero lambda-prime 231 couplings. The search relies upon the approximate lepton universality in the Standard Model, the sign of the charge of the proton, and a collection of favourable detector biases. The proposed search is unusual because: it does not require any of the displaced vertices, hadronic neutralino decay products, or squark/gluino production relied upon by existing LHC RPV searches; it could work in cases in which the only light sparticles were smuons and neutralinos; and it could make a discovery (though not necessarily with optimal significance) without requiring the computation of a leading-order Monte Carlo estimate of any background rate. The LHC has shown no strong hints of post-Higgs physics and so precision Standard Model measurements are becoming ever more important. We argue that in this environment growing profits are to be made from searches that place detector biases and symmetries of the Standard Model at their core - searches based around `controls' rather than around signals.

    hep-phJHEP(2017)·8 citations
18. 18*

    Domain wall network as QCD vacuum: confinement, chiral symmetry, hadronization

    Sergei N. Nedelko🇷🇺 · Vladimir E. Voronin🇷🇺

    An approach to QCD vacuum as a medium describable in terms of statistical ensemble of almost everywhere homogeneous Abelian (anti-)self-dual gluon fields is reviewed. These fields play the role of the confining medium for color charged fields as well as underline the mechanism of realization of chiral $S{U}_{\mathrm{L}}(N_f)\times S{U}_{\mathrm{R}}(N_f)$ and $U_{\mathrm{A}}(1)$ symmetries. Hadronization formalism based on this ensemble leads to manifestly defined quantum effective meson action. Strong, electromagnetic and weak interactions of mesons are represented in the action in terms of nonlocal $n$-point interaction vertices given by the quark-gluon loops averaged over the background ensemble. Systematic results for the mass spectrum and decay constants of radially excited light, heavy-light mesons and heavy quarkonia are presented. Relationship of this approach to the results of functional renormalization group and Dyson-Schwinger equations, and the picture of harmonic confinement is briefly outlined.

    hep-phEPJ Web Conf.(2017)·0 citations
19. 19*

    Testing Higgs Coupling Precision and New Physics Scales at Lepton Colliders

    Shao-Feng Ge🇩🇪 · Hong-Jian He🇨🇳 · Rui-Qing Xiao🇨🇳

    The next-generation lepton colliders, such as CEPC, FCC-ee, and ILC will make precision measurement of the Higgs boson properties. We first extract the Higgs coupling precision from Higgs observables at CEPC to illustrate the potential of future lepton colliders. Depending on the related event rates, the precision can reach percentage level for most couplings. Then, we try to estimate the new physics scales that can be indirectly probed with Higgs and electroweak precision observables. The Higgs observables, together with the existing electroweak precision observables, can probe new physics up to 10TeV (40TeV for the gluon-related operator ${\mathcal{O}}_g$) at 95% C.L. Including the $Z/W$ mass measurements and $Z$-pole observables at CEPC further pushes the limit up to 35TeV. Although $Z$-pole running is originally for the purpose of machine calibration, it can be as important as the Higgs observables for probing the new physics scales indirectly. The indirect probe of new physics scales at lepton colliders can mainly cover the energy range to be explored by the following hadron colliders of pp (50-100TeV), such as SPPC and FCC-hh.

    hep-phhep-exInt.J.Mod.Phys.A(2016)·14 citations
20. 20*

    Sterile neutrino searches at future $e^{-}{e}^{+}$, $pp$, and $e^{-}p$ colliders

    Stefan Antusch🇨🇭 · Eros Cazzato🇨🇭 · Oliver Fischer🇨🇭

    Sterile neutrinos are among the most attractive extensions of the SM to generate the light neutrino masses observed in neutrino oscillation experiments. When the sterile neutrinos are subject to a protective symmetry, they can have masses around the electroweak scale and potentially large neutrino Yukawa couplings, which makes them testable at planned future particle colliders. We systematically discuss the production and decay channels at electron-positron, proton-proton and electron-proton colliders and provide a complete list of the leading order signatures for sterile neutrino searches. Among other things, we discuss several novel search channels, and present a first look at the possible sensitivities for the active-sterile mixings and the heavy neutrino masses. We compare the performance of the different collider types and discuss their complementarity.

    hep-phInt.J.Mod.Phys.A(2017)·254 citations
21. 21*

    Update of the Hadronic Vacuum Polarisation Contribution to the muon g-2

    Michel Davier🇫🇷

    Precise data on e^+e^- to hadrons have recently become available and are used to compute the lowest-order hadronic vacuum polarisation contribution to the muon magnetic anomaly through dispersion relations. This is the case for the dominant pi+ pi- channel, but the most significant progress comes from the near completion of the BABAR program of measuring exclusive processes below 2 GeV with the initial-state radiation method which allows an efficient coverage of a large range of energies.. In this paper we briefly review the data treatment, the achieved improvements, and the result obtained for the full Standard Model prediction of the muon magnetic anomaly. The value obtained, a_mu (had~LO)=(692.6 +- 3.3)x 10^{-10} is 20% more precise than our last estimate in 2010. It deviates from the direct experimental determination by (27.4 +- 7.6)x 10^{-10} (3.6 sigma). Perpectives for further improvement are discussed.

    hep-phNucl.Part.Phys.Proc.(2017)·38 citations
22. 22*

    Probing the BFKL dynamics in inclusive three jet production at the LHC

    F. Caporale🇪🇸 · F. G. Celiberto🇮🇹 · G. Chachamis🇪🇸 · D. Gordo Gomez🇪🇸 · A. Sabio Vera🇪🇸

    We propose the study of new observables in LHC inclusive events with three tagged jets, one in the forward direction, one in the backward direction and both well-separated in rapidity from the each other (Mueller-Navelet jets), together with a third jet tagged in central regions of rapidity. Since non-tagged associated mini-jet multiplicity is allowed, we argue that projecting the cross sections on azimuthal-angle components can provide several distinct tests of the BFKL dynamics. Realistic LHC kinematical cuts are introduced.

    hep-phEPJ Web Conf.(2017)·35 citations
23. 23*

    TeV Solar Gamma Rays From Cosmic-Ray Interactions

    Bei Zhou🇺🇸 · Kenny C. Y. Ng🇮🇱 · John F. Beacom🇺🇸 · Annika H. G. Peter🇺🇸

    The Sun is a bright source of GeV gamma rays, due to cosmic rays interacting with solar matter and photons. Key aspects of the underlying processes remain mysterious. The emission in the TeV range, for which there are neither observational nor theoretical studies, could provide crucial clues. The new experiments HAWC (running) and LHAASO (planned) can look at the Sun with unprecedented sensitivity. In this paper, we predict the very high-energy (up to 1000 TeV) gamma-ray flux from the solar disk and halo, due to cosmic-ray hadrons and electrons ($e^{+}+e^{-}$), respectively. We neglect solar magnetic effects, which is valid at TeV energies; at lower energies, this gives a theoretical lower bound on the disk flux and a theoretical upper bound on the halo flux. We show that the solar-halo gamma-ray flux allows the first test of the $\sim 5$--70 TeV cosmic-ray electron spectrum. Further, we show that HAWC can immediately make an even stronger test with nondirectional observations of cosmic-ray electrons. Together, these gamma-ray and electron studies will provide new insights about the local density of cosmic rays and their interactions with the Sun and its magnetic environment. These studies will also be an important input to tests of new physics, including dark matter.

    ↳ astro-ph.HEastro-ph.SRhep-phPRD(2017)·60 citations
24. 24*

    Cosmological constant vis-a-vis dynamical vacuum: bold challenging the $\Lambda$CDM

    Joan Sola🇪🇸

    Next year we will celebrate 100 years of the cosmological term, $\Lambda$, in Einstein's gravitational field equations, also 50 years since the cosmological constant problem was first formulated by Zeldovich, and almost about two decades of the observational evidence that a non-vanishing, positive, $\Lambda$-term could be the simplest phenomenological explanation for the observed acceleration of the Universe. This mixed state of affairs already shows that we do no currently understand the theoretical nature of $\Lambda$. In particular, we are still facing the crucial question whether $\Lambda$ is truly a fundamental constant or a mildly evolving dynamical variable. At this point the matter should be settled once more empirically and, amazingly enough, the wealth of observational data at our disposal can presently shed true light on it. In this short review I summarize the situation of some of these studies. It turns out that the $\Lambda =$const. hypothesis, despite being the simplest, may well not be the most favored one when we put it in hard-fought competition with specific dynamical models of the vacuum energy. Recently it has been shown that the overall fit to the cosmological observables $SNIa+BAO+H(z)+LSS+BBN+CMB$ do favor the class of "running" vacuum models (RVM's) -- in which $\Lambda =\Lambda (H)$ is a function of the Hubble rate -- against the "concordance" $\Lambda$CDM model. The support is at an unprecedented level of $\sim 4\sigma$ and is backed up with Akaike and Bayesian criteria leading to compelling evidence in favor of the RVM option and other related dynamical vacuum models. I also address the implications of this framework on the possible time evolution of the fundamental constants of Nature.

    ↳ astro-ph.COgr-qchep-phhep-thInt.J.Mod.Phys.A(2016)·64 citations
25. 25*

    Non-equilibrium study of the Chiral Magnetic Effect from real-time simulations with dynamical fermions

    Mark Mace🇺🇸 · Niklas Mueller🇩🇪 · Sören Schlichting🇺🇸 · Sayantan Sharma🇺🇸

    We present a real-time lattice approach to study the non-equilibrium dynamics of vector and axial charges in $SU(N)\times U(1)$ gauge theories. Based on a classical description of the non-Abelian and Abelian gauge fields, we include dynamical fermions and develop operator definitions for (improved) Wilson and overlap fermions that allow us to study real-time manifestations of the axial anomaly from first principles. We present a first application of this approach to anomalous transport phenomena such as the Chiral Magnetic Effect (CME) and Chiral Separation Effect (CSE) by studying the dynamics of fermions during and after a $SU(N)$ sphaleron transition in the presence of a $U(1)$ magnetic field. We investigate the fermion mass and magnetic field dependence of the suggested signatures of the CME and CSE and point out some important aspects which need to be accounted for in the macroscopic description of anomalous transport phenomena.

    ↳ hep-lathep-phnucl-thPRD(2017)·71 citations
26. 26*

    Hiding neutrino mass in modified gravity cosmologies

    Nicola Bellomo🇪🇸 · Emilio Bellini🇪🇸 · Bin Hu🇪🇸 · Raul Jimenez🇪🇸 · Carlos Pena-Garay🇪🇸 · Licia Verde🇪🇸

    Cosmological observables show a dependence with the neutrino mass, which is partially degenerate with parameters of extended models of gravity. We study and explore this degeneracy in Horndeski generalized scalar-tensor theories of gravity. Using forecasted cosmic microwave background and galaxy power spectrum datasets, we find that a single parameter in the linear regime of the effective theory dominates the correlation with the total neutrino mass. For any given mass, a particular value of this parameter approximately cancels the power suppression due to the neutrino mass at a given redshift. The extent of the cancellation of this degeneracy depends on the cosmological large-scale structure data used at different redshifts. We constrain the parameters and functions of the effective gravity theory and determine the influence of gravity on the determination of the neutrino mass from present and future surveys.

    ↳ astro-ph.COhep-phJCAP(2017)·57 citations
27. 27*

    Constraints and prospects on GW and neutrino emissions using GW150914

    Krijn D. de Vries🇧🇪 · Gwenhaël de Wasseige🇧🇪 · Jean-Marie Frère🇧🇪 · Matthias Vereecken🇧🇪

    Recently, the LIGO observatory reported the first direct observation of gravitational waves, with a signal consistent with a binary black hole merger. This detection triggered several follow-up searches for coincident emission in electromagnetic waves as well as neutrinos, but no such emission was found. In this article, the implications of the non-detection of counterpart neutrinos are investigated using general arguments. The results are interpreted with a parameter denoting the energy emitted in neutrinos relative to the energy emitted in gravitational waves. The bound on this parameter from the diffuse astrophysical neutrino flux detected by the IceCube Neutrino Observatory is discussed. It is found that, currently, the non-detection of counterpart neutrinos puts a bound comparable to the one from the diffuse astrophysical neutrino flux. This bound is then used to constrain the amount of matter in the black hole binary environment. Finally, the sensitivity to this parameter in future gravitational wave observation runs is investigated. It is shown how the detection of one or more neutrinos from a single merger would strongly constrain the source population and evolution.

    ↳ astro-ph.HEhep-phPRD(2017)·5 citations
28. 28*

    Including heavy spin effects in the prediction of a $\bar{b}\bar{b}ud$ tetraquark with lattice QCD potentials

    Pedro Bicudo🇵🇹 · Jonas Scheunert🇩🇪 · Marc Wagner🇩🇪

    We investigate spin effects in four-quark systems consisting of two heavy anti-bottom quarks and two light up/down quarks. To this end we use the Born-Oppenheimer approximation. We utilize potentials of two static antiquarks in the presence of two quarks of finite mass computed via lattice QCD and solve a coupled-channel Schrödinger equation for the anti-bottom-anti-bottom separation. Without taking heavy quark spins into account this approach predicted a $ud\bar{b}\bar{b}$ tetraquark bound state with quantum numbers $I(J^P)=0(1^{+})$. We now extend this Born-Oppenheimer approach with coupled channel Schrödinger equations allowing us to incorporate effects due to the heavy $\bar{b}$ spins. We confirm the existence of the $ud\bar{b}\bar{b}$ tetraquark.

    ↳ hep-lathep-phPRD(2017)·119 citations
29. 29*

    Lorentz invariance violation and simultaneous emission of electromagnetic and gravitational waves

    E. Passos🇧🇷 · M.A. Anacleto🇧🇷 · F.A. Brito🇧🇷 · O. Holanda🇧🇷 · G.B. Souza🇧🇷 · C.A.D. Zarro🇧🇷

    In this work, we compute some phenomenological bounds for the electromagnetic and massive gravitational high-derivative extensions supposing that it is possible to have an astrophysical process that generates simultaneously gravitational and electromagnetic waves. We present Lorentz invariance violating (LIV) higher-order derivative models, following the Myers-Pospelov approach, to electrodynamics and massive gravitational waves. We compute the corrected equation of motion of these models, their dispersion relations and the velocities. The LIV parameters for the gravitational and electromagnetic sectors, ${\xi }_g$ and ${\xi }_{\gamma }$, respectively, were also obtained for three different approaches: luminal photons, time delay of flight and the difference of graviton and photon velocities. These LIV parameters depend on the mass scales where the LIV-terms become relevant, $M$ for the electromagnetic sector and $M_1$ for the gravitational one. We obtain, using the values for $M$ and $M_1$ found in the literature, that ${\xi }_g\sim 10^{-2}$, which is expected to be phenomenologically relevant and ${\xi }_{\gamma }\sim 10^3$, which cannot be suitable for an effective LIV theory. However, we show that ${\xi }_{\gamma }$ can be interesting in a phenomenological point of view if $M\gg M_1$. Finally the relation between the variation of the velocities of the photon and the graviton in relation to the speed of light was calculated and resulted in $\Delta v_g/\Delta v_{\gamma }\lesssim 1.82\times 10^{-3}$.

    ↳ hep-thgr-qchep-phPLB(2017)·9 citations
30. 30*

    Schwinger's proper time and worldline holographic renormalisation

    Dennis D. Dietrich🇩🇪 · Adrian Koenigstein🇩🇪

    Worldline holography states that within the framework of the worldline approach to quantum field theory, sources of a quantum field theory over Mink${}_4$ naturally form a field theory over AdS${}_5$ {\sl to all orders} in the elementary fields and in the sources of arbitrary spin. (Such correspondences are also available for other pairs of spacetimes, not only Mink${}_4\leftrightarrow {\mathrm{AdS}}_5$.) Schwinger's proper time of the worldline formalism is automatically grouped with the physical four spacetime dimensions into an AdS${}_5$ geometry. We show that the worldline holographic effective action in general and the proper-time profiles of the sources in particular solve a renormalisation group equation and, reversely, can be defined as solution to the latter. This fact also ensures regulator independence.

    ↳ hep-thhep-phnucl-thPRD(2017)·2 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.