Tue·Jul 25, 2017Tuesday·July 25, 2017

1. 01*

   Bottom-quark Fusion Processes at the LHC for Probing $Z^{\prime }$ Models and B-meson Decay Anomalies

   Mohammad Abdullah🇺🇸 · Mykhailo Dalchenko🇺🇸 · Bhaskar Dutta🇺🇸 · Ricardo Eusebi🇺🇸 · Peisi Huang🇺🇸 · Teruki Kamon🇺🇸 · Denis Rathjens🇺🇸 · Adrian Thompson🇺🇸

   We investigate models of a heavy neutral gauge boson Z' which could explain anomalies in B meson decays reported by the LHCb experiment. In these models, the Z' boson couples mostly to third generation fermions. We show that bottom quarks arising from gluon splitting can fuse into Z' as an essential production mechanism at the LHC, thereby allowing to probe these models. The study is performed within a generic framework for explaining the B anomalies that can be accommodated in well motivated models. The flavor violating b s coupling associated with Z' in such models produces lower bound on the production cross-section which gives rise to a cross-section range for such scenarios for the LHC to probe. Results are presented in Z' -> $\mu \mu$ decays with at least one bottom-tagged jet in its final state. Some parts of the model parameter space become constrained by the existing dimuon-resonance searches by the ATLAS and CMS collaborations. However, the requirement of one or two additional bottom-tagged jets in the final state would allow for probing a larger region of the parameter space of the models at the ongoing LHC program.

   hep-phPRD(2018)·41 citations
2. 02*

   Unified Halo-Independent Formalism From Convex Hulls for Direct Dark Matter Searches

   Graciela B. Gelmini🇺🇸 · Ji-Haeng Huh🇨🇭 · Samuel J. Witte🇪🇸

   Using the Fenchel-Eggleston theorem for convex hulls (an extension of the Caratheodory theorem), we prove that any likelihood can be maximized by either a dark matter 1- speed distribution $F(v)$ in Earth's frame or 2- Galactic velocity distribution $f^{\mathrm{gal}}(\vec{u})$, consisting of a sum of delta functions. The former case applies only to time-averaged rate measurements and the maximum number of delta functions is $(\mathcal{N}-1)$, where $\mathcal{N}$ is the total number of data entries. The second case applies to any harmonic expansion coefficient of the time-dependent rate and the maximum number of terms is $\mathcal{N}$. Using time-averaged rates, the aforementioned form of $F(v)$ results in a piecewise constant unmodulated halo function ${\tilde{\eta }}_{BF}^0(v_{\min })$ (which is an integral of the speed distribution) with at most $(\mathcal{N}-1)$ downward steps. The authors had previously proven this result for likelihoods comprised of at least one extended likelihood, and found the best-fit halo function to be unique. This uniqueness, however, cannot be guaranteed in the more general analysis applied to arbitrary likelihoods. Thus we introduce a method for determining whether there exists a unique best-fit halo function, and provide a procedure for constructing either a pointwise confidence band, if the best-fit halo function is unique, or a degeneracy band, if it is not. Using measurements of modulation amplitudes, the aforementioned form of $f^{\mathrm{gal}}(\vec{u})$, which is a sum of Galactic streams, yields a periodic time-dependent halo function ${\tilde{\eta }}_{BF}(v_{\min },t)$ which at any fixed time is a piecewise constant function of $v_{\min }$ with at most $\mathcal{N}$ downward steps. In this case, we explain how to construct pointwise confidence and degeneracy bands from the time-averaged halo function. Finally, we show that requiring an isotropic ...

   hep-phastro-ph.COJCAP(2017)·26 citations
3. 03*

   Different Realizations of Cooper-Frye Sampling with Conservation Laws

   C. Schwarz🇩🇪 · D. Oliinychenko🇺🇦 · L.-G. Pang🇺🇸 · S. Ryu🇩🇪 · H. Petersen🇩🇪

   Approaches based on viscous hydrodynamics for the hot and dense stage and hadronic transport for the final dilute rescattering stage are successfully applied to the dynamic description of heavy ion reactions at high beam energies. One crucial step in such hybrid approaches is the so called particlization, the transition between the hydrodynamic description to microscopic degrees of freedom. For this purpose, individual particles are sampled on the Cooper-Frye hypersurface. In this work, 4 different realizations of sampling algorithms are compared, where three of them incorporate global conservation laws of quantum numbers in each event. The algorithms are compared within two types of scenarios: simple "box" hypersurface consisting of only one static cell and a typical particlization hypersurface for Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV. For all algorithms the mean multiplicities (or particle spectra) remain unaffected by global conservation laws in the case of large volumes. In contrast, the fluctuations of the particle numbers are affected considerably. The fluctuations of the newly developed SPREW algorithm based on exponential weights and the recently suggested SER algorithm based on ensemble rejection are smaller than without conservation laws and agree with the expectation from the canonical ensemble. The previously applied mode sampling algorithm produces dramatically larger fluctuations, than it is expected in the corresponding microcanonical ensemble, and therefore should be avoided in fluctuation studies. This study might be of interest for investigations of particle fluctuations and correlations, e.g. the suggested signatures for a phase transition or a critical endpoint, in hybrid approaches that are affected by global conservation laws.

   hep-phnucl-thJ.Phys.G(2018)·17 citations
4. 04*

   A Framework for Finding Anomalous Objects at the LHC

   Amit Chakraborty🇯🇵 · Abhishek M. Iyer🇮🇳 · Tuhin S. Roy🇮🇳

   Search for new physics events at the LHC mostly rely on the assumption that the events are characterized in terms of standard-reconstructed objects such as isolated photons, leptons, and jets initiated by QCD-partons. While such strategy works for a vast majority of physics beyond the standard model scenarios, there are examples aplenty where new physics give rise to anomalous objects (such as collimated and equally energetic particles, decays due to long lived particles etc.) in the detectors, which can not be classified as any of the standard-objects. Varied methods and search strategies have been proposed, each of which is trained and optimized for specific models, topologies, and model parameters. Further, as LHC keeps excluding all expected candidates for new physics, the need for a generic method/tool that is capable of finding the unexpected can not be understated. In this paper, we propose one such method that relies on the philosophy that all anomalous objects are $not$ standard-objects. The anomaly finder, we suggest, simply is a collection of vetoes that eliminate all standard-objects up to a pre-determined acceptance rate. Any event containing at least one anomalous object (that passes all these vetoes), can be identified as a candidate for new physics. Subsequent offline analyses can determine the nature of the anomalous object as well as of the event, paving a robust way to search for these new physics scenarios in a model-independent fashion. Further, since the method relies on learning only the standard-objects, for which control samples are readily available from data, one can build the analysis in an entirely data-driven way.

   hep-phhep-exNPB(2018)·27 citations
5. 05*

   $Q\bar{Q}$ ($Q\in \{b,c\}$) spectroscopy using Cornell potential

   N. R. Soni🇮🇳 · B. R. Joshi🇮🇳 · R. P. Shah🇮🇳 · H. R. Chauhan🇮🇳 · J. N. Pandya🇮🇳

   The mass spectra and decay properties of heavy quarkonia are computed in nonrelativistic quark-antiquark Cornell potential model. We have employed the numerical solution of Schrödinger equation to obtain their mass spectra using only four parameters namely quark mass ($m_c$, $m_b$) and confinement strength ($A_{c\bar{c}}$, $A_{b\bar{b}}$). The spin hyperfine, spin-orbit and tensor components of the one gluon exchange interaction are computed perturbatively to determine the mass spectra of excited $S$, $P$, $D$ and $F$ states. Digamma, digluon and dilepton decays of these mesons are computed using the model parameters and numerical wave functions. The predicted spectroscopy and decay properties for quarkonia are found to be consistent with available experimental observations and results from other theoretical models. We also compute mass spectra and life time of the $B_c$ meson without additional parameters. The computed electromagnetic transition widths of heavy quarkonia and $B_c$ mesons are in tune with available experimental data and other theoretical approaches.

   hep-phEPJC(2018)·116 citations
6. 06*

   The s-Channel Single Top Quark Production as a Constraint for $W^{\prime }$ Boson Contribution

   Seyed Yaser Ayazi🇮🇷 · Saeid Paktinat Mehdiabadi🇮🇷

   An analysis is performed to constrain the $W^{\prime }$ boson production using the measurement of the s-channel single top quark production cross section. Both phenomenological and statistical approaches are examined and results are presented. In the best case, $W^{\prime }$ bosons that interact only to the right-handed fermions are excluded below 1390 GeV. To our knowledge, it is the first time that the measured cross section of the s-channel single top quark production from the colliders is used to rule out part of the phase space of the $W^{\prime }$ boson.

   hep-ph2 citations
7. 07*

   Holographic estimate of the meson cloud contribution to nucleon axial form factor

   G. Ramalho🇧🇷

   We use light-front Holography to estimate the valence quark and the meson cloud contributions to the nucleon axial form factor. The free couplings of the holographic model are determined by the empirical data and by the information extracted from lattice QCD. The holographic model provides a good description of the empirical data when we consider a meson cloud mixture of about 30\% in the physical nucleon state. The estimate of the valence quark contribution to the nucleon axial form factor compares well with the lattice QCD data for small pion masses. Our estimate of the meson cloud contribution to the nucleon axial form factor has a slower falloff with the square momentum transfer compared to typical estimates from quark models with meson cloud dressing.

   hep-phhep-exhep-latnucl-ex+1PRD(2018)·12 citations
8. 08*

   Production of $f_0(500)$, $f_0(980)$ and $a_0(980)$ in the ${\chi }_{c1}\to \eta {\pi }^{+}{\pi }^{-}$ and ${\eta }_c\to \eta {\pi }^{+}{\pi }^{-}$ decays

   V. R. Debastiani🇪🇸 · Wei-Hong Liang🇨🇳 · Ju-Jun Xie🇨🇳 · E. Oset🇪🇸

   Using the chiral unitary approach in coupled channels and $SU(3)$ symmetry we describe the production of $f_0(500)$, $f_0(980)$ and $a_0(980)$ in the ${\chi }_{c1}\to \eta {\pi }^{+}{\pi }^{-}$ reaction, recently performed by the BESIII collaboration. A very strong peak for the $a_0(980)$ can be seen in the $\eta \pi$ invariant mass, while clear signals for the $f_0(500)$ and $f_0(980)$ appear in the one of ${\pi }^{+}{\pi }^{-}$. Next, we make predictions for the analogous decay ${\eta }_c\to \eta {\pi }^{+}{\pi }^{-}$, which could also be measured experimentally. We discuss the differences of these reactions which are interesting to test the picture where these scalar mesons are dynamically generated from the interaction of pairs of pseudoscalars.

   hep-phActa Phys.Polon.Supp.(2017)·2 citations
9. 09*

   Migdal Effect in Dark Matter Direct Detection Experiments

   Masahiro Ibe🇯🇵 · Wakutaka Nakano🇯🇵 · Yutaro Shoji🇯🇵 · Kazumine Suzuki🇯🇵

   The elastic scattering of an atomic nucleus plays a central role in dark matter direct detection experiments. In those experiments, it is usually assumed that the atomic electrons around the nucleus of the target material immediately follow the motion of the recoil nucleus. In reality, however, it takes some time for the electrons to catch up, which results in ionization and excitation of the atoms. In previous studies, those effects are taken into account by using the so-called Migdal's approach, in which the final state ionization/excitation are treated separately from the nuclear recoil. In this paper, we reformulate the Migdal's approach so that the "atomic recoil" cross section is obtained coherently, where we make transparent the energy-momentum conservation and the probability conservation. We show that the final state ionization/excitation can enhance the detectability of rather light dark matter in the GeV mass range via the {\it nuclear} scattering. We also discuss the coherent neutrino-nucleus scattering, where the same effects are expected.

   hep-phhep-exJHEP(2018)·340 citations
10. 10*

    $\psi (2S)$ versus $J/\psi$ suppression in proton-nucleus collisions from factorization violating soft color exchanges

    Yan-Qing Ma🇨🇳 · Raju Venugopalan🇺🇸 · Kazuhiro Watanabe🇨🇳 · Hong-Fei Zhang🇨🇳

    We argue that the large suppression of the $\psi (2S)$ inclusive cross-section relative to the $J/\psi$ inclusive cross-section in proton-nucleus (p+A) collisions can be attributed to factorization breaking effects in the formation of quarkonium. These factorization breaking effects arise from soft color exchanges between charm-anticharm pairs undergoing hadronization and comoving partons that are long-lived on time scales of quarkonium formation. We compute the short distance pair production of heavy quarks in the Color Glass Condensate (CGC) effective field theory and employ an improved Color Evaporation model (ICEM) to describe their hadronization into quarkonium at large distances. The combined CGC+ICEM model provides a quantitative description of $J/\psi$ and $\psi (2S)$ data in proton-proton (p+p) collisions from both RHIC and the LHC. Factorization breaking effects in hadronization, due to additional parton comovers in the nucleus, are introduced heuristically by imposing a cutoff $\Lambda$, representing the momentum kick from soft color exchanges, in the ICEM model. Such soft exchanges have no perceptible effect on $J/\psi$ suppression in p+A collisions. In contrast, the interplay of the physics of these soft exchanges at large distances, with the physics of semi-hard rescattering at short distances, causes a significant additional suppression of $\psi (2S)$ yields relative to that of the $J/\psi$. A good fit of all RHIC and LHC $J/\psi$ and $\psi (2S)$ data, for transverse momenta $P_{\perp }\le 5$ GeV in p+p and p+A collisions, is obtained for $\Lambda \sim 10$ MeV.

    hep-phhep-exnucl-exnucl-thPRC(2018)·58 citations
11. 11*

    Neutrino mass and the Higgs portal dark matter in the ESSFSM

    Najimuddin Khan🇮🇳

    We extend the standard model with three right-handed singlet neutrinos and a real singlet scalar. We impose two $Z_2$ and $Z_2^{\prime }$-symmetries. We explain the tiny neutrino mass-squared differences with two $Z_2$- and $Z_2^{\prime }$-even right-handed neutrinos using the type-I seesaw mechanism. The $Z_2$-odd fermion and the $Z_2^{\prime }$-odd scalar can both serve as viable dark matter candidates. We identify new regions in the parameter space which are consistent with relic density of the dark matter, recent direct search experiment LUX-2016, XENON1T-2017 and LHC data.

    hep-phAdv.High Energy Phys.(2018)·4 citations
12. 12*

    Long-distance effects in $B\to K^{\ast }\ell \ell$ from Analyticity

    Christoph Bobeth🇩🇪 · Marcin Chrzaszcz🇨🇭 · Danny van Dyk🇨🇭 · Javier Virto🇩🇪

    We discuss a novel approach to systematically determine the long-distance contribution to $B\to K^{\ast }\ell \ell$ decays in the kinematic region where the dilepton invariant mass is below the open charm threshold. This approach provides the most consistent and reliable determination to date and can be used to compute Standard Model predictions for all observables of interest, including the kinematic region where the dilepton invariant mass lies between the $J/\psi$ and the $\psi (2S)$ resonances. We illustrate the power of our results by performing a New Physics fit to the Wilson coefficient $C_9$. This approach is systematically improvable from theoretical and experimental sides, and applies to other decay modes of the type $B\to V\ell \ell$, $B\to P\ell \ell$ and $B\to V\gamma$.

    hep-phhep-exEPJC(2018)·199 citations
13. 13*

    Sudakov suppression of jets in QCD media

    Yacine Mehtar-Tani🇺🇸 · Konrad Tywoniuk🇨🇭

    We compute modifications to the jet spectrum in the presence of a dense medium. We show that in the large-$N_c$ approximation and at leading logarithmic accuracy the jet nuclear modification factor factorizes into a quenching factor associated to the total jet color charge and a Sudakov suppression factor which accounts for the energy loss of jet substructure fluctuations. This factor, called the jet collimator, implements the fact that subjets, that are not resolved by the medium, lose energy coherently as a single color charge, whereas resolved large angle fluctuations suffer more quenching. For comparison, we show that neglecting color coherence results in a stronger suppression of the jet nuclear modification factor.

    hep-phnucl-thPRD(2018)·86 citations
14. 14*

    Clockwork seesaw mechanisms

    Seong Chan Park🇰🇷 · Chang Sub Shin🇰🇷

    We propose new mechanisms for small neutrino masses based on clockwork mechanism. The Standard Model neutrinos and lepton number violating operators communicate through the zero mode of clockwork gears, one of the two couplings of the zero mode is exponentially suppressed by clockwork mechanism. Including all known examples for the clockwork realization of the neutrino masses, different types of models are realized depending on the profile and chirality of the zero mode fermion. Each type of realization would have phenomenologically distinctive features with the accompanying heavy neutrinos.

    hep-phPLB(2018)·27 citations
15. 15*

    Resonances in positron scattering on a supercritical nucleus and spontaneous production of $e^{+}{e}^{-}$ pairs

    S.I. Godunov🇷🇺 · B. Machet🇫🇷 · M.I. Vysotsky🇷🇺

    We re-examine the physics of supercritical nuclei, specially focusing on the scattering phase ${\delta }_{\varkappa }$ and its dependence on the energy $\epsilon$ of the diving electronic level, for which we give both exact and approximate formulas. The Coulomb potential $Z\alpha /r$ is rounded to the constant $Z\alpha /R$ for $r<R$. We confirm the resonant behavior of ${\delta }_{\varkappa }$ that we investigate in details. In addition to solving the Dirac equation for an electron, we solve it for a positron, in the field of the same nucleus. This clarifies the interpretation of the resonances. Our results are compared with claims made in previous works.

    hep-phnucl-exnucl-thEPJC(2017)·24 citations
16. 16*

    Excited Hadrons and Quark-Hadron Duality

    E. Ruiz Arriola🇪🇸 · P. Masjuan🇪🇸 · W. Broniowski🇵🇱

    We review how Quark-Hadron Duality (QHD) for (u,d) flavors at high energies and in the scaling regime suggests a radial and angular behaviour of mesonic and baryonic resonance masses of the Regge form $M_{nJ}^2={\mu }^{2}n+{\beta }^{2}J+M_0^2$. The radial mass dependence is asymptotically consistent with a common two-body dynamics for mesons and baryons in terms of the quark-antiquark ($q\bar{q})$ and quark-diquark ($qD$) degrees of freedom, respectively. This formula is validated phenomenologically within an uncertainty determined by half the width of the resonances, $\Delta M_{nJ}^2\sim {\Gamma }_{nJ}{M}_{nJ}$. With this error prescription we find from the non-strange PDG hadrons different radial slopes ${\mu }_{\bar{q}q}^2=1.34(4){\mathrm{GeV}}^2$ and ${\mu }_{qD}^2=0.75(3){\mathrm{GeV}}^2$, but similar angular slopes ${\beta }_{\bar{q}q}^2\sim {\beta }_{qD}^2\sim 1.15{\mathrm{GeV}}^2$.

    hep-phnucl-thActa Phys.Polon.Supp.(2017)·4 citations
17. 17*

    Structure of rapidity divergences in soft factors

    Alexey Vladimirov🇩🇪

    We discuss the structure of rapidity divergences that are presented in the soft factors of transverse momentum dependent (TMD) factorization theorems. To provide the discussion on the most general level we consider soft factors for multi-parton scattering. We show that the rapidity divergences are result of the gluon exchanges with the distant transverse plane, and are structurally equivalent to the ultraviolet divergences. It allows to formulate and to prove the renormalization theorem for rapidity divergences. The proof is made with the help the conformal transformation which maps rapidity divergences to ultraviolet divergences. The theorem is the systematic form of the factorization of rapidity divergences, which is required for the definition of TMD parton distributions. In particular, the definition of multi parton distributions is presented. The equivalence of ultraviolet and rapidity divergences leads to the exact relation between soft and rapidity anomalous dimensions. Using this relation we derive the rapidity anomalous dimension at the three-loop order.

    hep-phJHEP(2018)·114 citations
18. 18*

    A new way to determine the neutrino mass hierarchy at reactors

    Luca Stanco · Giuseppe Salamanna · Alexey Lokhov · Fatma Sawy · Chiara Sirignano

    The determination of the neutrino mass ordering is currently pursued by several experiments and proposals. A very challenging one is its evaluation from reactor experiments based on the tiny interference effect between the $\Delta m_{31}^2$ and $\Delta m_{32}^2$ oscillations. Current analyses require several years of data taking and an extreme energy resolution to achieve anyhow less than 5 $\sigma$. Referring to the JUNO experimental conditions we developed a completely new technique that would provide a robust 5 $\sigma$ measurement in less than six years of running. The two orderings could be discriminated at the price of allowing for two different values of $\Delta m_{31}^2$. This degeneracy on $\Delta m_{31}^2$ (around $12\times 10^{-5}$ eV${}^2$) can however be measured at an unprecedented accuracy of much less than 1\%, i.e. $10^{-5}$ eV${}^2$, within the same analysis. Analogies with the usual ${\chi }^2$ analysis, where the $\Delta m_{31}^2$ degeneracy is much more important, are discussed. Evaluation and inclusion of systematic errors and backgrounds have been performed, the most relevant among them being the addition of the two remote reactor plants 250 km away. Baselines of each contributing reactor core and its spatial resolution have been taken into account. Possible results after two years of running and the foreseen initially-reduced available reactor power have been studied, too. These results confirm the very positive perspectives for JUNO to determine the mass ordering in a vacuum-oscillation dominated region.

    hep-phhep-ex11 citations
19. 19*

    Discovery of doubly-charmed Xi_{cc} baryon implies a stable (b b ubar dbar) tetraquark

    Marek Karliner🇮🇱 · Jonathan L. Rosner🇺🇸

    Recently LHCb discovered the first doubly-charmed baryon ${\Xi }_{cc}^{++}=ccu$ at $3621.40\pm 0.78$ MeV, very close to our theoretical prediction. We use the same methods to predict a doubly-bottom tetraquark $T(bb\bar{u}\bar{d})$ with $J^P=1^{+}$ at $10,389\pm 12$ MeV, 215 MeV below the $B^{-}{\bar{B}}^{\ast 0}$ threshold and 170 MeV below threshold for decay to $B^{-}{\bar{B}}^0\gamma$. The $T(bb\bar{u}\bar{d})$ is therefore stable under strong and electromagnetic (EM) interactions and can only decay weakly, the first exotic hadron with such a property. On the other hand, the mass of $T(cc\bar{u}\bar{d})$ with $J^P=1^{+}$ is predicted to be $3882\pm 12$ MeV, 7 MeV above the $D^0{D}^{\ast +}$ threshold and 148 MeV above $D^0{D}^{+}\gamma$ threshold. $T(bc\bar{u}\bar{d})$ with $J^P=0^{+}$ is predicted at $7134\pm 13$ MeV, 11 MeV below the ${\bar{B}}^0{D}^0$ threshold. Our precision is not sufficient to determine whether $bc\bar{u}\bar{d}$ is actually above or below the threshold. It could manifest itself as a narrow resonance just at threshold.

    hep-phhep-exPRL(2017)·343 citations
20. 20*

    Nucleon form factors in dispersively improved Chiral Effective Field Theory I: Scalar form factor

    J. M. Alarcón🇺🇸 · C. Weiss🇺🇸

    We propose a method for calculating the nucleon form factors (FFs) of $G$-parity-even operators by combining Chiral Effective Field Theory ($\chi$EFT) and dispersion analysis. The FFs are expressed as dispersive integrals over the two-pion cut at $t>4M_{\pi }^2$. The spectral functions are obtained from the elastic unitarity condition and expressed as products of the complex $\pi \pi \to N\bar{N}$ partial-wave amplitudes and the timelike pion FF. $\chi$EFT is used to calculate the ratio of the partial-wave amplitudes and the pion FF, which is real and free of $\pi \pi$ rescattering in the $t$-channel ($N/D$ method). The rescattering effects are then incorporated by multiplying with the squared modulus of the empirical pion FF. The procedure results in a marked improvement compared to conventional $\chi$EFT calculations of the spectral functions. We apply the method to the nucleon scalar FF and compute the scalar spectral function, the scalar radius, the $t$-dependent FF, and the Cheng-Dashen discrepancy. Higher-order chiral corrections are estimated through the $\pi N$ low-energy constants. Results are in excellent agreement with dispersion-theoretical calculations. We elaborate several other interesting aspects of our method. The results show proper scaling behavior in the large-$N_c$ limit of QCD because the $\chi$EFT calculation includes $N$ and $\Delta$ intermediate states. The squared modulus of the timelike pion FF required by our method can be extracted from Lattice QCD calculations of vacuum correlation functions of the operator at large Euclidean distances. Our method can be applied to the nucleon FFs of other operators of interest, such as the isovector-vector current, the energy-momentum tensor, and twist-2 QCD operators (moments of generalized parton distributions).

    hep-phhep-latnucl-thPRC(2017)·31 citations
21. 21*

    Astrophysical neutrinos flavored with Beyond the Standard Model physics

    Rasmus W. Rasmussen🇩🇪 · Lukas Lechner🇦🇹 · Markus Ackermann🇩🇪 · Marek Kowalski🇩🇪 · Walter Winter🇩🇪

    We systematically study the allowed parameter space for the flavor composition of astrophysical neutrinos measured at Earth, including beyond the Standard Model theories at production, during propagation, and at detection. One motivation is to illustrate the discrimination power of the next-generation neutrino telescopes such as IceCube-Gen2. We identify several examples that lead to potential deviations from the standard neutrino mixing expectation such as significant sterile neutrino production at the source, effective operators modifying the neutrino propagation at high energies, dark matter interactions in neutrino propagation, or non-standard interactions in Earth matter. IceCube-Gen2 can exclude about 90% of the allowed parameter space in these cases, and hence will allow to efficiently test and discriminate models. More detailed information can be obtained from additional observables such as the energy-dependence of the effect, fraction of electron antineutrinos at the Glashow resonance, or number of tau neutrino events.

    hep-phastro-ph.HEhep-exPRD(2017)·87 citations
22. 22*

    Charged Composite Scalar Dark Matter

    Reuven Balkin🇩🇪 · Maximilian Ruhdorfer🇩🇪 · Ennio Salvioni🇩🇪 · Andreas Weiler🇩🇪

    We consider a composite model where both the Higgs and a complex scalar $\chi$, which is the dark matter (DM) candidate, arise as light pseudo Nambu-Goldstone bosons (pNGBs) from a strongly coupled sector with TeV scale confinement. The global symmetry structure is $SO(7)/SO(6)$, and the DM is charged under an exact $U(1{)}_{\mathrm{DM}}\subset SO(6)$ that ensures its stability. Depending on whether the $\chi$ shift symmetry is respected or broken by the coupling of the top quark to the strong sector, the DM can be much lighter than the Higgs or have a weak-scale mass. Here we focus primarily on the latter possibility. We introduce the lowest-lying composite resonances and impose calculability of the scalar potential via generalized Weinberg sum rules. Compared to previous analyses of pNGB DM, the computation of the relic density is improved by fully accounting for the effects of the fermionic top partners. This plays a crucial role in relaxing the tension with the current DM direct detection constraints. The spectrum of resonances contains exotic top partners charged under the $U(1{)}_{\mathrm{DM}}$, whose LHC phenomenology is analyzed. We identify a region of parameters with $f=1.4\mathrm{TeV}$ and $200\mathrm{GeV}\lesssim m_{\chi }\lesssim 400\mathrm{GeV}$ that satisfies all existing bounds. This DM candidate will be tested by XENON1T in the near future.

    hep-phastro-ph.COJHEP(2017)·58 citations
23. 23*

    Multi-angle calculation of the matter-neutrino resonance near an accretion disk

    Shashank Shalgar🇺🇸

    We perform a numerical study of the matter-neutrino resonance in a multi-angle calculation in the vicinity of an accretion disk. We assume thermally distributed neutrino and anti-neutrino fields emitted by two-dimensional disk that is homogeneous and isotropic; the electrons are assumed to be at constant density. We compare the the result of this computation to that obtained using single-angle approximation. We investigate the robustness of matter-neutrino resonance in environment surrounding accretion disks by progressively relaxing the single angle approximation. We find that the multi-angle results in the present simplified model do not support a robust resonance mechanism as suggested by the single angle treatment. We also discuss the context under which matter-neutrino resonance may be important in future studies.

    hep-phastro-ph.HEnucl-thJCAP(2018)·20 citations
24. 24*

    Using CMB spectral distortions to distinguish between dark matter solutions to the small-scale crisis

    James A.D. Diacoumis🇦🇺 · Yvonne Y.Y. Wong🇦🇺

    The dissipation of small-scale perturbations in the early universe produces a distortion in the blackbody spectrum of cosmic microwave background photons. In this work, we propose to use these distortions as a probe of the microphysics of dark matter on scales $1{\text{Mpc}}^{-1}\lesssim k\lesssim 10^4{\text{Mpc}}^{-1}$. We consider in particular models in which the dark matter is kinetically coupled to either neutrinos or photons until shortly before recombination, and compute the photon heating rate and the resultant $\mu$-distortion in both cases. We show that the $\mu$-parameter is generally enhanced relative to $\Lambda$CDM for interactions with neutrinos, and may be either enhanced or suppressed in the case of interactions with photons. The deviations from the $\Lambda$CDM signal are potentially within the sensitivity reach of a PRISM-like experiment if ${\sigma }_{\text{DM}-\gamma }\gtrsim 1.1\times 10^{-30}\left(m_{\text{DM}}/\text{GeV}\right){\text{cm}}^2$ and ${\sigma }_{\text{DM}-\nu }\gtrsim 4.8\times 10^{-32}\left(m_{\text{DM}}/\text{GeV}\right){\text{cm}}^2$ for time-independent cross sections, and ${\sigma }_{\text{DM}-\gamma }^0\gtrsim 1.8\times 10^{-40}\left(m_{\text{DM}}/\text{GeV}\right){\text{cm}}^2$ and ${\sigma }_{\text{DM}-\nu }^0\gtrsim 2.5\times 10^{-47}\left(m_{\text{DM}}/\text{GeV}\right){\text{cm}}^2$ for cross sections scaling as temperature squared, coinciding with the parameter regions in which late kinetic decoupling may serve as a solution to the small-scale crisis. Furthermore, these $\mu$-distortion signals differ from those of warm dark matter (no deviation from $\Lambda$CDM) and a suppressed primordial power spectrum (strongly suppressed or a negative $\mu$-parameter), demonstrating that CMB spectral distortion can potentially be used to distinguish between solutions to the small-scale crisis.

    ↳ astro-ph.COhep-phJCAP(2017)·40 citations
25. 25*

    Distribution of the Dirac modes in QCD

    M. Catillo🇦🇹 · L. Ya. Glozman🇦🇹

    It was established that distribution of the near-zero modes of the Dirac operator is consistent with the Chiral Random Matrix Theory (CRMT) and can be considered as a consequence of spontaneous breaking of chiral symmetry (SBCS) in QCD. The higher-lying modes of the Dirac operator carry information about confinement physics and are not affected by SBCS. We study distributions of the near-zero and higher-lying modes of the overlap Dirac operator within $N_F=2$ dynamical simulations. We find that distributions of both near-zero and higher-lying modes are the same and follow the Gaussian Unitary Ensemble of Random Matrix Theory. This means that randomness, while consistent with SBCS, is not a consequence of SBCS and is related to some more general property of QCD in confinement regime.

    ↳ hep-lathep-phhep-thEPJ Web Conf.(2018)·2 citations
26. 26*

    Nonperturbative renormalization of nonlocal quark bilinears for quasi-PDFs on the lattice using an auxiliary field

    Jeremy Green🇩🇪 · Karl Jansen🇩🇪 · Fernanda Steffens🇩🇪

    Quasi-PDFs provide a path toward an ab initio calculation of parton distribution functions (PDFs) using lattice QCD. One of the problems faced in calculations of quasi-PDFs is the renormalization of a nonlocal operator. By introducing an auxiliary field, we can replace the nonlocal operator with a pair of local operators in an extended theory. On the lattice, this is closely related to the static quark theory. In this approach, we show how to understand the pattern of mixing that is allowed by chiral symmetry breaking, and obtain a master formula for renormalizing the nonlocal operator that depends on three parameters. We present an approach for nonperturbatively determining these parameters and use perturbation theory to convert to the MS-bar scheme. Renormalization parameters are obtained for two lattice spacings using Wilson twisted mass fermions and for different discretizations of the Wilson line in the nonlocal operator. Using these parameters we show the effect of renormalization on nucleon matrix elements with pion mass approximately 370 MeV, and compare renormalized results for the two lattice spacings. The renormalized matrix elements are consistent among the different Wilson line discretizations and lattice spacings.

    ↳ hep-lathep-phPRL(2018)·192 citations
27. 27*

    Birdtracks for SU(N)

    Stefan Keppeler🇩🇪

    I gently introduce the diagrammatic birdtrack notation, first for vector algebra and then for permutations. After moving on to general tensors I review some recent results on Hermitian Young operators, gluon projectors, and multiplet bases for SU(N) color space.

    ↳ math-phhep-phhep-thmath.MPSciPost Phys.Lect.Notes(2018)·24 citations
28. 28*

    A signature of anisotropic cosmic-ray transport in the gamma-ray sky

    Silvio Sergio Cerri🇮🇹 · Daniele Gaggero🇳🇱 · Andrea Vittino🇩🇪 · Carmelo Evoli🇮🇹 · Dario Grasso🇮🇹

    A crucial process in Galactic cosmic-ray (CR) transport is the spatial diffusion due to the interaction with the interstellar turbulent magnetic field. Usually, CR diffusion is assumed to be uniform and isotropic all across the Galaxy. However, this picture is clearly inaccurate: Several data-driven and theoretical arguments, as well as dedicated numerical simulations, show that diffusion exhibits highly anisotropic properties with respect to the direction of a background (ordered) magnetic field (i.e., parallel or perpendicular to it). In this paper we focus on a recently discovered anomaly in the hadronic CR spectrum inferred by the Fermi-LAT gamma-ray data at different positions in the Galaxy, i.e. the progressive hardening of the proton slope at low Galactocentric radii. We propose the idea that this feature can be interpreted as a signature of anisotropic diffusion in the complex Galactic magnetic field: In particular, the harder slope in the inner Galaxy is due, in our scenario, to the parallel diffusive escape along the poloidal component of the large-scale, regular, magnetic field. We implement this idea in a numerical framework, based on the DRAGON code, and perform detailed numerical tests on the accuracy of our setup. We discuss how the effect proposed depends on the relevant free parameters involved. Based on low-energy extrapolation of the few focused numerical simulations aimed at determining the scalings of the anisotropic diffusion coefficients, we finally present a set of plausible models that reproduce the behavior of the CR proton slopes inferred by gamma-ray data.

    ↳ astro-ph.HEhep-phJCAP(2017)·63 citations
29. 29*

    Squeezed relic photons beyond the horizon

    Massimo Giovannini🇨🇭

    Owing to the analogy with the ordinary photons in the visible range of the electromagnetic spectrum, the Glauber theory is generalized to address the quantum coherence of the gauge field fluctuations parametrically amplified during an inflationary stage of expansion. The first and second degrees of quantum coherence of relic photons are then computed beyond the effective horizon defined by the evolution of the susceptibility. In the zero-delay limit the Hanbury Brown-Twiss correlations exhibit a super-Poissonian statistics which is however different from the conventional results of the single-mode approximation customarily employed, in quantum optics, to classify the coherence properties of visible light. While in the case of large-scale curvature perturbations the degrees of quantum coherence coincide with the naive expectation of the single-mode approximation, the net degree of second-order coherence computed for the relic photons diminishes thanks to the effect of the polarizations. We suggest that the Hanbury Brown-twiss correlations are probably the only tool to assess the quantum or classical origin of the large-scale magnetic fluctuations and of the corresponding curvature perturbations.

    ↳ gr-qcastro-ph.COhep-phhep-thPRD(2017)·1 citation

* 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.