Fri·Dec 23, 2016Friday·December 23, 2016

1. 01*

   Augury of Darkness: The Low-Mass Dark Z' Portal

   Alexandre Alves🇧🇷 · Giorgio Arcadi🇩🇪 · Yann Mambrini🇫🇷 · Stefano Profumo🇺🇸 · Farinaldo S. Queiroz🇩🇪

   Dirac fermion dark matter models with heavy $Z^{\prime }$ mediators are subject to stringent constraints from spin-independent direct searches and from LHC bounds, cornering them to live near the $Z^{\prime }$ resonance. Such constraints can be relaxed, however, by turning off the vector coupling to Standard Model fermions, thus weakening direct detection bounds, or by resorting to light $Z^{\prime }$ masses, below the Z pole, to escape heavy resonance searches at the LHC. In this work we investigate both cases, as well as the applicability of our findings to Majorana dark matter. We derive collider bounds for light $Z^{\prime }$ gauge bosons using the $C{L}_S$ method, spin-dependent scattering limits, as well as the spin-independent scattering rate arising from the evolution of couplings between the energy scale of the mediator mass and the nuclear energy scale, and indirect detection limits. We show that such scenarios are still rather constrained by data, and that near resonance they could accommodate the gamma-ray GeV excess in the Galactic center.

   hep-phastro-ph.HEhep-exJHEP(2017)·39 citations
2. 02*

   Dark Matter's secret liaisons: phenomenology of a dark U(1) sector with bound states

   Marco Cirelli🇫🇷 · Paolo Panci🇨🇭 · Kalliopi Petraki🇫🇷 · Filippo Sala🇫🇷 · Marco Taoso🇪🇸

   Dark matter (DM) charged under a dark U(1) force appears in many extensions of the Standard Model, and has been invoked to explain anomalies in cosmic-ray data, as well as a self-interacting DM candidate. In this paper, we perform a comprehensive phenomenological analysis of such a model, assuming that the DM abundance arises from the thermal freeze-out of the dark interactions. We include, for the first time, bound-state effects both in the DM production and in the indirect detection signals, and quantify their importance for Fermi, AMS, and CMB experiments. We find that DM in the mass range 1 GeV to 100 TeV, annihilating into dark photons of MeV to GeV mass, is in conflict with observations. Instead, DM annihilation into heavier dark photons is viable. We point out that the late decays of multi-GeV dark photons can produce significant entropy and thus dilute the DM density. This can lower considerably the dark coupling needed to obtain the DM abundance, and in turn relax the existing constraints.

   hep-phastro-ph.COastro-ph.HEJCAP(2017)·188 citations
3. 03*

   Point-Particle Effective Field Theory I: Classical Renormalization and the Inverse-Square Potential

   C.P. Burgess🇨🇦 · Peter Hayman🇨🇦 · Matt Williams🇧🇪 · Laszlo Zalavari🇨🇦

   Singular potentials (the inverse-square potential, for example) arise in many situations and their quantum treatment leads to well-known ambiguities in choosing boundary conditions for the wave-function at the position of the potential's singularity. These ambiguities are usually resolved by developing a self-adjoint extension of the original problem; a non-unique procedure that leaves undetermined which extension should apply in specific physical systems. We take the guesswork out of this picture by using techniques of effective field theory to derive the required boundary conditions at the origin in terms of the effective point-particle action describing the physics of the source. In this picture ambiguities in boundary conditions boil down to the allowed choices for the source action, but casting them in terms of an action provides a physical criterion for their determination. The resulting extension is self-adjoint if the source action is real (and involves no new degrees of freedom), and not otherwise (as can also happen for reasonable systems). We show how this effective-field picture provides a simple framework for understanding well-known renormalization effects that arise in these systems, including how renormalization-group techniques can resum non-perturbative interactions that often arise, particularly for non-relativistic applications. In particular we argue why the low-energy effective theory tends to produce a universal RG flow of this type and describe how this can lead to the phenomenon of reaction {\em catalysis}, in which physical quantities (like scattering cross sections) can sometimes be surprisingly large compared to the underlying scales of the source in question. We comment in passing on the possible relevance of these observations to the phenomenon of the catalysis of baryon-number violation by scattering from magnetic monopoles.

   hep-phhep-thquant-phJHEP(2017)·30 citations
4. 04*

   Strange fireball as an explanation of the muon excess in Auger data

   Luis A. Anchordoqui🇺🇸 · Haim Goldberg🇺🇸 · Thomas J. Weiler🇺🇸

   We argue that ultrahigh energy cosmic ray collisions in the Earth atmosphere can probe the strange quark density of the nucleon. These collisions have center-of-mass energies \agt 10^{4.6} A GeV, where A \geq 14 is the nuclear baryon number. We hypothesize the formation of a deconfined thermal fireball which undergoes a sudden hadronization. At production the fireball has a very high matter density and consists of gluons and two flavors of light quarks (u,d). Because the fireball is formed in the baryon-rich projectile fragmentation region, the high baryochemical potential damps the production of u \bar u and d \bar d pairs, resulting in gluon fragmentation mainly into s \bar s. The strange quarks then become much more abundant and upon hadronization the relative density of strange hadrons is significantly enhanced over that resulting from a hadron gas. Assuming the momentum distribution functions can be approximated by Fermi-Dirac and Bose-Einstein statistics, we estimate a kaon-to-pion ratio of about 3 and expect a similar (total) baryon-to-pion ratio. We show that, if this were the case, the excess of strange hadrons would suppress the fraction of energy which is transferred to decaying \pi^0's by about 20\%, yielding a \sim 40\% enhancement of the muon content in atmospheric cascades, in agreement with recent data reported by the Pierre Auger Collaboration.

   hep-phastro-ph.HEPRD(2017)·60 citations
5. 05*

   Point-Particle Effective Field Theory II: Relativistic Effects and Coulomb/Inverse-Square Competition

   C.P. Burgess🇨🇦 · Peter Hayman🇨🇦 · Markus Rummel🇨🇦 · Matt Williams🇧🇪 · Laszlo Zalavari🇨🇦

   We apply point-particle effective field theory (PPEFT) to compute the leading shifts due to finite-size source effects in the Coulomb bound energy levels of a relativistic spinless charged particle. This is the analogue for spinless electrons of the contribution of the charge-radius of the source to these levels, and we disagree with standard calculations in several ways. Most notably we find there are two effective interactions with the same dimension that contribute to leading order in the nuclear size. One is the standard charge-radius contribution, while the other is a contact interaction whose leading contribution to $\delta E$ arises linearly in the small length scale, $ϵ$, characterizing the finite-size effects, and is suppressed by $(Z\alpha {)}^5$. We argue that standard calculations miss the contributions of this second operator because they err in their choice of boundary conditions at the source for the wave-function of the orbiting particle. PPEFT predicts how this boundary condition depends on the source's charge radius, as well as on the orbiting particle's mass. Its contribution turns out to be crucial if the charge radius satisfies $ϵ\lesssim (Z\alpha {)}^2{a}_B$, with $a_B$ the Bohr radius, since then relativistic effects become important. We show how the problem is equivalent to solving the Schrödinger equation with competing Coulomb, inverse-square and delta-function potentials, which we solve explicitly. A similar enhancement is not predicted for the hyperfine structure, due to its spin-dependence. We show how the charge-radius effectively runs due to classical renormalization effects, and why the resulting RG flow is central to predicting the size of the energy shifts. We discuss how this flow is relevant to systems having much larger-than-geometric cross sections, and the possible relevance to catalysis of reactions through scattering with monopoles.

   hep-phhep-thquant-phJHEP(2017)·20 citations
6. 06*

   The Proton Radius Problem and Point-Particle Effective Field Theory

   C.P. Burgess🇨🇦 · Peter Hayman🇨🇦 · Markus Rummel🇨🇦 · Laszlo Zalavari🇨🇦

   We argue that the proton's charge-radius contributes differently to shifts of Hydrogen-like energy levels than naively expected due to an incorrect choice for the boundary condition at the proton's position in standard calculations. In particular we show how to obtain the correct boundary condition, which depends on the charge radius itself in a predictable way. We argue this difference in boundary conditions only matters when they are imposed at a radius $r=ϵ<Z\alpha /m$ where $m$ is the orbiting-particle mass, because only then is the particle relativistic at these distances. The boundary condition difference is therefore important for ordinary Hydrogen while not for muonic Hydrogen. The boundary condition can be interpreted in terms of a second type of nuclear moment, and a prediction is made for the proton-radius energy shift as a function of charge-radius, $r_p$, this second nuclear moment, $h$, and orbiting particle mass, $m$. The observed difference between electronic and muonic contributions to the Lamb shift is accounted for with $r_p\simeq 0.87$ fm similar to its traditional value, and $2mh$ of order a few fm.

   hep-ph4 citations
7. 07*

   Towards New Frontiers in the Exploration of Charmless Non-Leptonic $B$ Decays

   Robert Fleischer🇳🇱 · Ruben Jaarsma🇳🇱 · K. Keri Vos🇩🇪

   Non-leptonic $B$ decays into charmless final states offer an important laboratory to study CP violation and the dynamics of strong interactions. Particularly interesting are $B_s^0\to K^{-}{K}^{+}$ and $B_d^0\to {\pi }^{-}{\pi }^{+}$ decays, which are related by the $U$-spin symmetry of strong interactions, and allow for the extraction of CP-violating phases and tests of the Standard Model. The theoretical precision is limited by $U$-spin-breaking corrections and innovative methods are needed in view of the impressive future experimental precision expected in the era of Belle II and the LHCb upgrade. We have recently proposed a novel method to determine the $B_s^0$-${\bar{B}}_s^0$ mixing phase ${\varphi }_s$ from the $B_s^0\to K^{-}{K}^{+}$, $B_d^0\to {\pi }^{-}{\pi }^{+}$ system, where semileptonic $B_s^0\to K^{-}{\ell }^{+}{\nu }_{\ell }$, $B_d^0\to {\pi }^{-}{\ell }^{+}{\nu }_{\ell }$ decays are a new ingredient and the theoretical situation is very favourable. We discuss this strategy in detail, with a focus on penguin contributions as well as exchange and penguin-annihilation topologies which can be probed by a variety of non-leptonic $B$ decays into charmless final states. We show that a theoretical precision as high as $\mathcal{O}(0.5^{\circ })$ for ${\varphi }_s$ can be attained in the future, thereby offering unprecedented prospects for the search for new sources of CP violation.

   hep-phhep-exJHEP(2017)·30 citations
8. 08*

   Probing CP violation with non-unitary mixing in long-baseline neutrino oscillation experiments: DUNE as a case study

   F. J. Escrihuela🇪🇸 · D. V. Forero🇺🇸 · O. G. Miranda🇲🇽 · M. Tórtola🇪🇸 · J. W. F. Valle🇪🇸

   When neutrino masses arise from the exchange of neutral heavy leptons, as in most seesaw schemes, the effective lepton mixing matrix $N$ describing neutrino propagation is non-unitary, hence neutrinos are not exactly orthonormal. New CP violation phases appear in $N$ that could be confused with the standard phase ${\delta }_{\text{CP}}$ characterizing the three neutrino paradigm. We study the potential of the long-baseline neutrino experiment DUNE in probing CP violation induced by the standard CP phase in the presence of non-unitarity. In order to accomplish this we develop our previous formalism, so as to take into account the neutrino interactions with the medium, important in long baseline experiments such as DUNE. We find that the expected CP sensitivity of DUNE is somewhat degraded with respect to that characterizing the standard unitary case. However the effect is weaker than might have been expected thanks mainly to the wide neutrino beam. We also investigate the sensitivity of DUNE to the parameters characterizing non-unitarity. In this case we find that there is no improvement expected with respect to the current situation, unless the near detector setup is revamped.

   hep-phhep-exNew J.Phys.(2017)·107 citations
9. 09*

   Quark and lepton masses and mixing from a gauged SU(3)_F family symmetry with a light O(eV) sterile Dirac neutrino

   Albino Hernandez-Galeana🇲🇽

   In the framework of a complete vector-like and universal gauged SU(3)_F family symmetry, we report a global region in the parameter space where this approach can account for a realistic spectrum of quark masses and mixing in a 4 x 4 non-unitary V_{CKM}, as well as for the known charged lepton masses and the squared neutrino mass differences reported from neutrino oscillation experiments. The $SU(3{)}_F$ family symmetry is broken spontaneously in two stages by heavy SM singlet scalars, whose hierarchy of scales yield and approximate SU(2)_F global symmetry associated to the almost degenerate boson masses of the order of the lower scale of the SU(3)_F SSB. The gauge symmetry, the fermion content, and the transformation of the scalar fields, all together, avoid Yukawa couplings between SM fermions. Therefore, in this scenario ordinary heavy fermions, top and bottom quarks and tau lepton, become massive at tree level from Dirac See-saw mechanisms, while light fermions, including light neutrinos, obtain masses from radiative corrections mediated by the massive gauge bosons of the SU(3)_F family symmetry. The displayed fit parameter space region solution for fermion masses and mixing yield the vector-like fermion masses: M_D \approx 3.2 \,TeV, M_U \approx 6.9 \,TeV, M_E \approx 21.6 \,TeV, SU(2)_F family gauge boson masses of $\mathcal{O}(2TeV)$, and the squared neutrino mass differences: m_2^2-m_1^2 \approx 7.5 x 10^{-5}\;eV^2, m_3^2-m_2^2 \approx 2.2 x 10^{-3}\;eV^2, m_4^2-m_1^2 \approx 0.82\;eV^2.

   hep-phBled Workshops Phys.(2016)·3 citations
10. 10*

    Azimuthal and spin asymmetries in $e^{+}{e}^{-}\to V\pi X$ at high energies and 3D fragmentation functions

    Kai-bao Chen🇨🇳

    We present the systematical decomposition results of three-dimensional (3D) fragmentation functions (FFs) from parton correlators for spin-1 hadron. We choose one of the best process $e^{+}{e}^{-}\to V\pi X$ to study the 3D and tensor polarization dependent FFs. By making a general kinematic analysis we show that the cross section is expressed by 81 independent structure functions, and get the results of the azimuthal and spin asymmetries. We also present the parton model results for this process and express the results in terms of the 3D FFs. Based on this formalism, we also give the numerical results of hadron longitudinal polarizations and predict the energy dependence.

    hep-ph0 citations
11. 11*

    Central Production of $\eta$ via Double Pomeron Exchange and Double Reggeon Exchange in the Sakai-Sugimoto Model

    Neil Anderson🇺🇸 · Sophia Domokos🇺🇸 · Nelia Mann🇺🇸

    We use holographic QCD to study Pomeron- and Reggeon-mediated central production in Regge regime hadronic scattering. We focus specifically on $\eta$ production in proton-proton collisions. While previous work studied the Pomeron-mediated process, the mesonic Regge trajectories ("Reggeons") we now incorporate contribute significantly at experimentally probed energies. We use the five-point open string amplitude (in flat space) to construct approximate propagators for the Reggeon states, and the five-point closed string amplitude for the Pomeron. Using these "holographic" Reggeons and Pomerons, and low-energy couplings derived in the Sakai-Sugimoto model, we compute the differential and total cross sections at $\sqrt{s}$ =29.1 GeV. Our calculation of the total cross section is $\sigma =236\mathrm{nb}$, while the experimentally measured value is $\sigma =3859\mathrm{nb}$. The discrepancy between our result and the measured value may indicate that our model systematically underestimates the values of the relevant coupling constants.

    hep-phhep-thPRD(2017)·19 citations
12. 12*

    Search for lepton flavor violation at future lepton colliders

    Gi-Chol Cho🇯🇵 · Hanako Shimo🇯🇵

    Lepton flavor violating (LFV) processes via four-Fermi contact interactions at future International Linear Collider (ILC) are studied. The effective Lagrangian is composed of six-operators, and the LFV effects on both $e^{+}{e}^{-}\to e^{+}{\ell }^{-}$ and $e^{-}{e}^{-}\to e^{-}{\ell }^{-}$ ($\ell =\mu$ or $\tau$) processes can be parametrized by three parameters. Taking account of previous experimental results of LFV processes $\mu \to 3e$ and $\tau \to 3e$, we find that the upper limits on the LFV parameters for $\ell =\tau$ could be improved at the ILC experiment using the polarized electron beam. The improvement of the upper limits is more than an order of magnitude smaller than previous ones.

    hep-phInt.J.Mod.Phys.A(2017)·7 citations
13. 13*

    Analysis of $P_c^{+}(4380)$ and $P_c^{+}(4450)$ as pentaquark states in the molecular picture with QCD sum rules

    K. Azizi🇹🇷 · Y. Sarac🇹🇷 · H. Sundu🇹🇷

    To better understand the nature and internal structure of the exotic states discovered by many collaborations, more information on their electromagnetic properties and their strong and weak interactions with other hadrons is needed. The residue or current coupling constant of these states together with their mass are the main inputs in determinations of such properties. We perform QCD sum rules analyses on the hidden-charm pentaquark states with spin-parities $J^P={\frac{3}{2}}^{\pm }$ and $J^P={\frac{5}{2}}^{\pm }$ to calculate their residue and mass. In the calculations, we adopt a molecular picture for $J^P={\frac{3}{2}}^{\pm }$ states and a mixed current in a molecular form for $J^P={\frac{5}{2}}^{\pm }$. Our analyses show that the $P_c^{+}(4380)$ and $P_c^{+}(4450)$, observed by LHCb Collaboration, can be considered as hidden-charm pentaquark states with $J^P={\frac{3}{2}}^{-}$ and $J^P={\frac{5}{2}}^{+}$, respectively.

    hep-phPRD(2017)·102 citations
14. 14*

    Testing ${\chi }_c$ properties at BELLE II

    Henryk Czyż🇵🇱 · Patrycja Kisza🇵🇱

    The model of the ${\chi }_{c_i}-{\gamma }^{\ast }-{\gamma }^{\ast }$ and ${\chi }_{c_i}-J/{\psi }^{\ast }-{\gamma }^{\ast }$ form factors developed in [1] for ${\chi }_{c_1}$ and ${\chi }_{c_2}$ is extended to ${\chi }_{c_0}$ case. The studies performed within this model have shown that at BELLE II it will be possible to study in detail ${\chi }_{c_i}-{\gamma }^{\ast }-\gamma$ form factors through measurements of the reaction $e^{+}{e}^{-}\to e^{+}{e}^{-}{\chi }_{c_i}(\to J/\psi (\to {\mu }^{+}{\mu }^{-})\gamma )$.The results were obtained using the newly updated Monte Carlo generator EKHARA.

    hep-phPLB(2017)·5 citations
15. 15*

    Magnetic-Field Induced Critical Endpoint

    Stefan Rechenberger🇩🇪

    The phase diagram of strong interaction matter is analyzed utilizing the Nambu--Jona-Lasinio model. Special emphasis is placed on its dependence on an external magnetic field and isospin chemical potential. Using flavor mixing induced by instanton effects the influence of isospin breaking due to the magnetic field and the isospin chemical potential is compared. It is found that at low temperatures and large quark chemical potential the magnetic field, depending on its strength, induces a new critical endpoint or a triple point.

    hep-phnucl-thPRD(2017)·9 citations
16. 16*

    Time reversal symmetry violation in entangled pseudoscalar neutral charmed mesons

    Yu Shi🇨🇳 · Jichong Yang🇨🇳

    The direct observation of time reversal symmetry violation (TV) is important for the test of $CPT$ conservation and the Standard Model. In this paper, we study both time-dependent and time-independent genuine TV signals in entangled $D^0-{\bar{D}}^0$ pairs. A possible $CPT$-violation effect called the $\omega$ effect is also investigated. In the $C=-1$ entangled state, the asymmetries due to TV are calculated to be of the order of $10^{-5}$ to $10^{-4}$ within the Standard Model, but the modification due to the $\omega$ effect in the $C=-1$ states is found to be about $10\%-30\%$ when $|\omega |\sim 10^{-4}$. This result is consistent with our Monte Carlo simulation, which implies that with $10^9$ to $10^{10}$ events, TV signals can be observed in the entangled $D^0-{\bar{D}}^0$ pairs, and the bound of $\omega \sim 10^{-3}$ can be reached. The time-dependent and the time-independent asymmetries in the $C=-1$ $D^0-{\bar{D}}^0$ system provides a window to detect new physics such as the $\omega$ effect, although they are not easily observable.

    hep-phPRD(2018)·16 citations
17. 17*

    Higgs Boson Production and Decay at Hadron Colliders

    Michael Spira🇨🇭

    Higgs physics at hadron colliders as the LHC is reviewed within the Standard Model (SM) and its minimal supersymmetric extension (MSSM) by summarizing the present state-of-the-art of theoretical predictions for the production cross sections and decay rates.

    hep-phhep-exPPNP(2017)·136 citations
18. 18*

    Resonant CP violation in rare tau decay

    Jilberto Zamora-Saa🇷🇺

    In this work, we study the lepton number violating tau decays via intermediate on-shell Majorana neutrinos $N_j$ into two scalar mesons and a lepton ${\tau }^{\pm }\to M_1{}^{\pm }{N}_j\to M_1^{\pm }{M}_2^{\pm }{\ell }^{\mp }$. We calculate the Branching ratios $Br({\tau }^{\pm })$ and the CP asymmetry $(\Gamma ({\tau }^{+})-\Gamma ({\tau }^{-}))/(\Gamma ({\tau }^{+})+\Gamma ({\tau }^{-}))$ for such decays, in a scenario that contain at least two heavy Majorana neutrinos. The results show that the CP asymmetry is small, but becomes comparable with the branching ratio $\mathrm{Br}({\tau }^{\pm })$ when their mass difference is comparable with their decay width, $\Delta M_N\sim {\Gamma }_N$. On the other hand, we present regions of the heavy-light neutrino mixing elements, in which the $CP$ asymmetry could be explore in future tau factories.

    hep-phJHEP(2017)·41 citations
19. 19*

    Minimal non-universal EW extensions of the Standard Model: a chiral multi-parameter solution

    Richard H. Benavides🇨🇴 · Luis Alfredo Muñoz🇨🇴 · William A. Ponce🇨🇴 · Oscar Rodríguez🇨🇴 · Eduardo Rojas🇨🇴

    We report the most general expression for the chiral charges of a non-universal $U(1{)}^{\prime }$ with identical charges for the first two families but different charges for the third one. The model is minimal in the sense that only standard model fermions plus right-handed neutrinos are required. By imposing anomaly cancellation and constraints coming from Yukawa couplings we obtain two different solutions. In one of these solutions, the anomalies cancel between fermions in different families. These solutions depend on four independent parameters which result very useful for model building. We build different benchmark models in order to show the flexibility of the parameterization. We also report LHC and low energy constraints for these benchmark models.

    hep-phPRD(2017)·5 citations
20. 20*

    Higgs-Boson Masses and Mixing Matrices in the NMSSM: Analysis of On-Shell Calculations

    Peter Drechsel🇩🇪 · Ramona Gröber🇬🇧 · Sven Heinemeyer🇪🇸 · Milada Margarete Muhlleitner🇩🇪 · Heidi Rzehak🇩🇰 · Georg Weiglein🇩🇪

    We analyze the Higgs-boson masses and mixing matrices in the NMSSM based on an on-shell (OS) renormalization of the gauge-boson and Higgs-boson masses and the parameters of the top/scalar top sector. We compare the implementation of the OS calculations in the codes NMSSMCALC and NMSSM-FeynHiggs up to $({\alpha }_t{\alpha }_s)$. We identify the sources of discrepancies at the one- and at the two-loop level. Finally we compare the OS and $\overline{\text{DR}}$ evaluation as implemented in NMSSMCALC. The results are important ingredients for an estimate of the theoretical precision of Higgs-boson mass calculations in the NMSSM.

    hep-phEPJC(2017)·33 citations
21. 21*

    Stacking machine learning classifiers to identify Higgs bosons at the LHC

    Alexandre Alves🇧🇷

    Machine learning (ML) algorithms have been employed in the problem of classifying signal and background events with high accuracy in particle physics. In this paper, we compare the performance of a widespread ML technique, namely, \emph{stacked generalization}, against the results of two state-of-art algorithms: (1) a deep neural network (DNN) in the task of discovering a new neutral Higgs boson and (2) a scalable machine learning system for tree boosting, in the Standard Model Higgs to tau leptons channel, both at the 8 TeV LHC. In a cut-and-count analysis, \emph{stacking} three algorithms performed around 16\% worse than DNN but demanding far less computation efforts, however, the same \emph{stacking} outperforms boosted decision trees. Using the stacked classifiers in a multivariate statistical analysis (MVA), on the other hand, significantly enhances the statistical significance compared to cut-and-count in both Higgs processes, suggesting that combining an ensemble of simpler and faster ML algorithms with MVA tools is a better approach than building a complex state-of-art algorithm for cut-and-count.

    hep-phcs.LGphysics.data-anJINST(2017)·16 citations
22. 22*

    Two-photon exchange corrections to elastic $e^{-}$-proton scattering: Full dispersive treatment of $\pi N$ states at low momentum transfers

    O. Tomalak🇩🇪 · B. Pasquini🇮🇹 · M. Vanderhaeghen🇩🇪

    We evaluate the pion-nucleon intermediate-state contribution to the two-photon exchange (TPE) correction in the elastic electron-nucleon scattering within a dispersive framework. We calculate the contribution from all $\pi N$ partial waves using the MAID parametrization. We provide the corresponding TPE correction to the unpolarized $ep$ scattering cross section in the region of low momentum transfer $Q^2\lesssim 0.064{\mathrm{GeV}}^2$, where no analytical continuation into the unphysical region of the TPE scattering amplitudes is required. We compare our result in the forward angular region with an alternative TPE calculation, in terms of structure functions, and find a good agreement, indicating a small contribution at low $Q^2$ due to discontinuities beyond $\pi N$. We also compare our results with empirical fits.

    hep-phnucl-exPRD(2017)·33 citations
23. 23*

    Nuclear Parton Distributions

    S. A. Kulagin🇷🇺

    We review a microscopic model of the nuclear parton distribution functions, which accounts for a number of nuclear effects including Fermi motion and nuclear binding, nuclear meson-exchange currents, off-shell corrections to bound nucleon distributions and nuclear shadowing. We also discuss applications of this model to a number of processes including lepton-nucleus deep inelastic scattering, proton-nucleus Drell-Yan lepton pair production at Fermilab, as well as W+- and Z0 boson production in proton-lead collisions at the LHC.

    hep-phEPJ Web Conf.(2017)·12 citations
24. 24*

    Axion-like particle production in a laser-induced dynamical spacetime

    M. A. Wadud🇬🇧 · B. King🇬🇧 · R. Bingham🇬🇧 · G. Gregori🇬🇧

    We consider the dynamics of a charged particle (e.g., an electron) oscillating in a laser field in flat spacetime and describe it in terms of the variable mass metric. By applying Einstein's equivalence principle, we show that, after representing the electron motion in a time-dependent manner, the variable mass metric takes the form of the Friedmann-Lemaître-Robertson-Walker metric. We quantize a massive complex scalar or pseudo-scalar field in this spacetime and derive the production rate of electrically neutral, spinless particle-antiparticle pairs. We show that this approach can provide an alternative experimental method to axion searches.

    hep-phPLB(2018)·5 citations
25. 25*

    On Longevity of I-ball/Oscillon

    Kyohei Mukaida🇯🇵 · Masahiro Takimoto🇯🇵 · Masaki Yamada🇯🇵

    We study I-balls/oscillons, which are long-lived, quasi-periodic, and spatially localized solutions in real scalar field theories. Contrary to the case of Q-balls, there is no evident conserved charge that stabilizes the localized configuration. Nevertheless, in many classical numerical simulations, it has been shown that they are extremely long-lived. In this paper, we clarify the reason for the longevity, and show how the exponential separation of time scales emerges dynamically. Those solutions are time-periodic with a typical frequency of a mass scale of a scalar field. This observation implies that they can be understood by the effective theory after integrating out relativistic modes. We find that the resulting effective theory has an approximate global U(1) symmetry reflecting an approximate number conservation in the non-relativistic regime. As a result, the profile of those solutions is obtained via the bounce method, just like Q-balls, as long as the breaking of the U(1) symmetry is small enough. We then discuss the decay processes of the I-ball/oscillon by the breaking of the U(1) symmetry, namely the production of relativistic modes via number violating processes. We show that the imaginary part is exponentially suppressed, which explains the extraordinary longevity of I-ball/oscillon. In addition, we find that there are some attractor behaviors during the evolution of I-ball/oscillon that further enhance the lifetime. The validity of our effective theory is confirmed by classical numerical simulations. Our formalism may also be useful to study condensates of ultra light bosonic dark matter, such as fuzzy dark matter, and axion stars, for instance.

    hep-phastro-ph.COhep-thJHEP(2017)·94 citations
26. 26*

    Detection prospects for high energy neutrino sources from the anisotropic matter distribution in the local universe

    Philipp Mertsch🇩🇰 · Mohamed Rameez🇩🇰 · Irene Tamborra (NBIA Copenhagen)🇩🇰

    Constraints on the number and luminosity of the sources of the cosmic neutrinos detected by IceCube have been set by targeted searches for point sources. We set complementary constraints by using the 2MASS Redshift Survey (2MRS) catalogue, which maps the matter distribution of the local Universe. Assuming that the distribution of the neutrino sources follows that of matter we look for correlations between `warm' spots on the IceCube skymap and the 2MRS matter distribution. Through Monte Carlo simulations of the expected number of neutrino multiplets and careful modelling of the detector performance (including that of IceCube-Gen2) we demonstrate that sources with local density exceeding $10^{-6}{\text{Mpc}}^{-3}$ and neutrino luminosity $L_{\nu }\lesssim 10^{42}\text{erg}{\text{s}}^{-1}$ ($10^{41}\text{erg}{\text{s}}^{-1}$) will be efficiently revealed by our method using IceCube (IceCube-Gen2). At low luminosities such as will be probed by IceCube-Gen2, the sensitivity of this analysis is superior to requiring statistically significant direct observation of a point source.

    ↳ astro-ph.HEastro-ph.COhep-phJCAP(2017)·29 citations
27. 27*

    Quasiparticle second-order viscous hydrodynamics from kinetic theory

    Leonardo Tinti🇺🇸 · Amaresh Jaiswal🇩🇪 · Radoslaw Ryblewski🇵🇱

    We present the derivation of second-order relativistic viscous hydrodynamics from an effective Boltzmann equation for a system consisting of quasiparticles of a single species. We consider temperature-dependent masses of the quasiparticles and devise a thermodynamically-consistent framework to formulate second-order evolution equations for shear and bulk viscous pressure corrections. The main advantage of this formulation is that one can consistently implement realistic equation of state of the medium within the framework of kinetic theory. Specializing to the case of one-dimensional purely-longitudinal boost-invariant expansion, we study the effect of this new formulation on viscous hydrodynamic evolution of strongly-interacting matter formed in relativistic heavy-ion collisions.

    ↳ nucl-thhep-phPRD(2017)·50 citations
28. 28*

    Chiral Magnetohydrodynamic Turbulence

    Petar Pavlović🇩🇪 · Natacha Leite🇩🇪 · Günter Sigl🇩🇪

    In this work the influence of the chiral anomaly effect on the evolution of magnetohydrodynamic turbulence was studied. We argue that in the early universe, before the electroweak symmetry breaking, and for temperatures high enough such that the electron mass can be ignored, the description of a charged plasma in general needs to take into account the interplay between turbulence and the anomaly effects. It was demonstrated that this generalization can have important consequences on the evolution of turbulence, leading to the creation of maximally-helical fields from initially non-helical ones. Therefore, chiral effects can strongly support turbulent inverse cascade, and lead to a slower decrease of the magnetic field with time, and also to a faster growth of the correlation length, when compared to the evolution predicted by the standard magnetohydrodynamical description. Using the weak anomaly approximation, and treating the anomaly contributions to magnetic energy and helicity as a small perturbation, we derive the specific solutions for the inverse cascade regime that demonstrate how chiral effects support the inverse cascade.

    ↳ astro-ph.COhep-phPRD(2017)·51 citations
29. 29*

    Mass and width of the $\Delta (1232)$ resonance using complex-mass renormalization

    T. Bauer🇩🇪 · Y. Unal🇩🇪 · A. Kucukarslan🇹🇷 · S. Scherer🇩🇪

    We discuss the pole mass and the width of the $\Delta (1232)$ resonance to third order in chiral effective field theory. In our calculation we choose the complex-mass renormalization scheme (CMS) and show that the CMS provides a consistent power-counting scheme. In terms of the pion-mass dependence, we compare the convergence behavior of the CMS with the small-scale expansion (SSE).

    ↳ nucl-thhep-lathep-phPRC(2017)·2 citations
30. 30*

    More on the Bending of Light in Quantum Gravity

    Dong Bai🇨🇳 · Yue Huang🇨🇳

    We reconsider the long-range effects of the scattering of massless scalars and photons from a massive scalar object in quantum gravity. At the one-loop level, the relevant quantum mechanical corrections could be sorted into the graviton double-cut contributions, massless-scalar double-cut contributions and photon double-cut contributions. In arXiv:1410.7590 and 1609.07477 N.E.J. Bjerrum-Bohr et al. have considered explicitly the implications of the graviton double-cut contributions on the gravitational bending of light and some classical formulations of the equivalence principle, using the modern double-copy constructions and on-shell unitarity techniques. In this article, instead we consider all three contributions and redo the analysis using the traditional Feynman diagrammatic approach. Our results on the graviton double-cut contributions agree with the aforementioned references, which acts as a nontrivial check of previous computations. Furthermore, it turns out that the massless-scalar double-cut contributions and the photon double-cut contributions do leave non-vanishing quantum effects on the scattering amplitudes and the gravitational bending of light. Yet, we find that the general structure of the gravitational amplitudes and the quantum discrepancy of the equivalence principle suggested in the aforementioned references remain intact.

    ↳ hep-thgr-qchep-phPRD(2017)·57 citations
31. 31*

    Novel cosmic-ray electron and positron constraints on MeV dark matter particles

    Mathieu Boudaud🇫🇷 · Julien Lavalle🇫🇷 · Pierre Salati🇫🇷

    MeV dark matter (DM) particles annihilating or decaying to electron-positron pairs cannot, in principle, be observed via local cosmic-ray (CR) measurements because of the shielding solar magnetic field. In this letter, we take advantage of spacecraft Voyager 1's capacity for detecting interstellar CRs since it crossed the heliopause in 2012. This opens up a new avenue to probe DM in the sub-GeV energy/mass range that we exploit here for the first time. From a complete description of the transport of electrons and positrons at low energy, we derive predictions for both the secondary astrophysical background and the pair production mechanisms relevant to DM annihilation or decay down to the MeV mass range. Interestingly, we show that reacceleration may push positrons up to energies larger than the DM particle mass. We combine the constraints from the Voyager and AMS-02 data to get novel limits covering a very extended DM particle mass range, from MeV to TeV. In the MeV mass range, our limits reach annihilation cross sections of order $⟨\sigma v⟩\sim 10^{-28}\mathrm{c}{\mathrm{m}}^3/s$. An interesting aspect is that these limits barely depend on the details of cosmic-ray propagation in the weak reacceleration case, a configuration which seems to be favored by the most recent boron-to-carbon ($B/C$) data. Though extracted from a completely different and new probe, these bounds have a strength similar to those obtained with the cosmic microwave background --- they are even more stringent for $p$-wave annihilation.

    ↳ astro-ph.HEhep-phPRL(2017)·136 citations
32. 32*

    Strong isospin violation and chiral logarithms in the baryon spectrum

    David A. Brantley🇺🇸 · Balint Joo🇺🇸 · Ekaterina V. Mastropas🇺🇸 · Emanuele Mereghetti🇺🇸 · Henry Monge-Camacho🇺🇸 · Brian C. Tiburzi🇺🇸 · Andre Walker-Loud🇺🇸

    We present a precise lattice QCD calculation of the contribution to the neutron-proton mass splitting arising from strong isospin breaking, $m_n-m_p{|}_{QCD}=2.32\pm 0.17$ MeV. We also determine $m_{{\Xi }^{-}}-m_{{\Xi }^0}{|}_{QCD}=5.44\pm 0.31$ MeV. The calculation is performed at three values of the pion mass, with several values of the quark mass splitting and multiple lattice volumes, but only a single lattice spacing and an estimate of discretization errors. The calculations are performed on the anisotropic clover-Wilson ensembles generated by the Hadron Spectrum Collaboration. The omega-baryon mass is used to set the scale $a_t^{-1}=6111\pm 127$ MeV, while the kaon masses are used to determine the value of the light-quark mass spitting. The nucleon mass splitting is then determined as a function of the pion mass. We observe, for the first time, conclusive evidence for non-analytic light quark mass dependence in lattice QCD calculations of the baryon spectrum. When left as a free parameter, the fits prefer a nucleon axial coupling of $g_A=1.24(56)$. To highlight the presence of this chiral logarithm in the nucleon mass splitting, we also compute the isospin splitting in the cascade-baryon system which is less sensitive to chiral dynamics. Finally, we update the best lattice QCD determination of the CP-odd pion-nucleon coupling that would arise from a non-zero QCD theta-term, ${\bar{g}}_0/(\sqrt{2}{f}_{\pi })=(14.7\pm 1.8\pm 1.4)\cdot 10^{-3}\bar{\theta }$. The original lattice QCD correlation functions, analysis results and extrapolated quantities are packaged in HDF5 files made publicly available including a simple Python script to access the numerical results, construct effective mass plots along with our analysis results, and perform the extrapolations of various quantities determined in this work.

    ↳ hep-lathep-phnucl-th45 citations
33. 33*

    Planck Constraint on Relic Primordial Black Holes

    Steven Clark🇺🇸 · Bhaskar Dutta🇺🇸 · Yu Gao🇺🇸 · Louis E. Strigari🇺🇸 · Scott Watson🇺🇸

    We investigate constraints on the abundance of primordial black holes (PBHs) in the mass range 10^{15}-10^{17} g using data from the Cosmic Microwave Background (CMB) and MeV extragalactic gamma-ray background (EGB). Hawking radiation from PBHs with lifetime greater than the age of the universe leaves an imprint on the CMB through modification of the ionization history and the damping of CMB anisotropies. Using a model for redshift dependent energy injection efficiencies, we show that a combination of temperature and polarization data from Planck provides the strongest constraint on the abundance of PBHs for masses \sim 10^{15}-10^{16} g, while the EGB dominates for masses \gtrsim 10^{16} g. Both the CMB and EGB now rule out PBHs as the dominant component of dark matter for masses \sim 10^{16}-10^{17} g. Planned MeV gamma-ray observatories are ideal for further improving constraints on PBHs in this mass range.

    ↳ astro-ph.COhep-phPRD(2017)·173 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.