hep-ph updates on
High Energy Physics - Phenomenology (hep-ph) updates on the e-print archive
  • Amplifying dark matter indirect detection signal by thermal effects at freeze-out. (arXiv:1801.06184v1 [hep-ph])

    Authors: Andi Hektor, Kristjan Kannike, Ville Vaskonen

    We present an extension of the Standard Model, containing a fermion dark matter candidate and two real scalar singlets, where the observed dark matter abundance is produced via freeze-out before the electroweak phase transition. We show that in this case the dark matter annihilation channels determining its freeze-out are different from those producing indirect detection signal. We present a benchmark model where the indirect annihilation cross-section is significantly larger than the freeze-out one. The model also has a gravitational wave signature due to the first order electroweak phase transition.

  • Renormalization scheme and gauge (in)dependence of the generalized Crewther relation: what are the real grounds of the $\beta$-factorization property?. (arXiv:1801.06231v1 [hep-ph])

    Authors: A. V. Garkusha, A. L. Kataev, V. S. Molokoedov

    The scheme and gauge dependence of the factorization property of the RG $\beta$-function in the $SU(N_c)$ QCD generalized Crewther relation (GCR), which connects the non-singlet contributions to the Adler and Bjorken polarized sum rule functions, is investigated at the $\mathcal{O}(a^4_s)$ level. In the gauge-invariant $\rm{\overline{MS}}$-scheme this property holds at least at this order. To study whether this property is true in all gauge-invariant schemes, we consider the $\rm{MS}$-like schemes in QCD and the QED-limit of the GCR in the $\rm{\overline{MS}}$-scheme and in the $\rm{MOM}$ and the $\rm{OS}$ schemes. In these schemes we confirm the existence of the $\beta$-function factorization in the QCD and QED variants of the GCR. The problem of the possible $\beta$-factorization in the gauge-dependent renormalization schemes in QCD is studied. We consider the gauge non-invariant $\rm{mMOM}$ and $\rm{MOMgggg}$-schemes and demonstrate that in the $\rm{mMOM}$ scheme at the $\mathcal{O}(a^3_s)$ level the $\beta$-factorization is valid for three values of the gauge parameter $\xi$ only, namely for $\xi=-3, -1$ and $\xi=0$. In the $\mathcal{O}(a^4_s)$ order of PT it remains valid only for case of the Landau gauge $\xi=0$.

    The consideration of these two schemes for the QCD GCR allows us to conclude that the factorization of RG $\beta$-function will always be implemented in any $\rm{MOM}$-like schemes with linear covariant gauge at $\xi=0$ and $\xi=-3$ at the $\mathcal{O}(a^3_s)$ level. It is demonstrated that if factorization property for the $\rm{MS}$-like schemes is true in all orders of PT, as theoretically indicated, then the factorization will also occur in the arbitrary $\rm{MOM}$-like scheme in the Landau gauge in all orders of PT as well.

  • Two clock transitions in neutral Yb for the highest sensitivity to variations of fundamental constants. (arXiv:1801.06239v1 [physics.atom-ph])

    Authors: M. S. Safronova, S. G. Porsev, Christian Sanner, Jun Ye

    We propose a new frequency standard based on a $4f^{14} 6s6p~ ^3\!P_0 - 4f^{13} 6s^2 5d ~(J=2)$ transition in neutral Yb. This transition has a potential for high stability and accuracy and the advantage of the highest sensitivity among atomic clocks to variation of the fine-structure constant $\alpha$. We find its dimensionless $\alpha$-variation enhancement factor to be $K=-15$, in comparison to the most sensitive current clock (Yb$^+$ E3, $K=-6$), and it is 18 times larger than in any neutral-atomic clocks (Hg, $K=0.8$). Combined with the unprecedented stability of an optical lattice clock for neutral atoms, this high sensitivity opens new perspectives for searches for ultralight dark matter and for tests of theories beyond the standard model of elementary particles. Moreover, together with the well-established $^1\!S_0 -\, ^3\!P_0$ transition one will have two clock transitions operating in neutral Yb, whose interleaved interrogations may further reduce systematic uncertainties of such clock-comparison experiments.

  • Axion-plasmon polaritons in strongly magnetized plasmas. (arXiv:1801.06254v1 [hep-ph])

    Authors: H. Terças, J. D. Rodrigues, J. T. Mendonça

    Axions are hypothetical particles related to the violation of the charge-parity symmetry, being the most prone candidates for dark matter. Multiple attempts to prove their existence are currently performed in different physical systems. Here, we anticipate the possibility of the axions coupling to the electrostatic (Langmuir) modes of a strongly magnetized plasma, by showing that a new quasi-particle can be defined, the axion-plasmon polariton. The excitation of axions can be inferred from the pronounced modification of the dispersion relation of the Langmuir waves, a feature that we estimate to be accessible in state-of-the-art plasma-based experiments. We further show that, under extreme density and magnetic field conditions (e.g. at the interior of dense neutron stars), the axion-plasmon polariton becomes dynamically unstable, similarly to the case of the Jeans instability occurring in self-gravitating fluids. This latter result anticipates a plausible mechanism to the creation of axion-like particles in the universe.

  • Hadron tomography and its application to gravitational radii of hadrons. (arXiv:1801.06264v1 [hep-ph])

    Authors: S. Kumano, Qin-Tao Song, O. V. Teryaev

    Hadron tomography has been investigated by three-dimensional structure functions, such as generalized parton distributions (GPDs) and generalized distribution amplitudes (GDAs). The GDAs are $s$-$t$ crossed quantities of the GPDs, and both functions probe gravitational form factors for hadrons. We determined the pion GDAs by analyzing Belle data on the differential cross section for the two-photon process $\gamma^* \gamma \to \pi^0 \pi^0$. From the determined GDAs, we calculated timelike gravitational form factors of the pion and they were converted to the spacelike form factors by using the dispersion relation. These gravitational form factors $\Theta_1$ and $\Theta_2$ indicate mechanical (pressure, shear force) and gravitational-mass (or energy) distributions, respectively. Then, gravitational radii are calculated for the pion from the form factors, and they are compared with the pion charge radius. We explain that the new field of gravitational physics can be developed in the microscopic level of quarks and gluons.

  • Kaon Structure in the confining Nambu-Jona-Lasino Model. (arXiv:1801.06299v1 [nucl-th])

    Authors: Parada. T. P. Hutauruk

    The elastic electromagnetic form factors in the space-like region and valence quark distribution functions for the K+ meson are calculated using the confining Nambu-Jona-Lasinio model with the help of the proper-time regularization scheme, which simulates quark confinement. In this model framework, the dynamics information on the nonperturbative aspects is obtained from quark propagators and bound state amplitudes via Bethe-Salpeter equations. We found that the results on the kaon form factors and valence quark distribution functions are qualitatively in excellent agreement with the existing kaon data as well as the perturbation QCD prediction at higher Q.

  • On phenomenological study of the solution of nonlinear GLR-MQ evolution equation beyond leading order using recent PDF data. (arXiv:1801.06360v1 [hep-ph])

    Authors: M. Lalung, P. Phukan, J. K. Sarma

    We present a phenomenological study of the small-x behaviour of gluon distribution function $G(x,Q^2)$ at next-to-leading order (NLO) and next-to-next-to-leading order(NNLO) in light of the nonlinear Gribov-Ryskin-Levin-Mueller-Qiu (GLR-MQ)evolution equation by keeping the trasverse size of the gluons ($\sim 1/Q$) fixed. We consider the NLO and NNLO corrections, of the gluon-gluon spitting function $P_{gg} (z)$ and strong coupling constant $\alpha_s (Q^2)$. We have suggested semi-analytical solutions based on Regge like ansatz of gluon density $G(x,Q^2)$, which are supposed to be valid in the moderate range of photon virtuality$(Q^2)$ and at small Bjorken variable$(x)$. The study of the effects of nonlinearities that arise due to gluon recombination effects at small-x is very interesting, which eventually tames down the unusual growth of gluon densities towards small-x as predicted by the linear DGLAP evolution equation.

  • Predictions for the Dirac CP-Violating Phase from Sum Rules. (arXiv:1801.06377v1 [hep-ph])

    Authors: Luis A. Delgadillo, Lisa L. Everett, Raymundo Ramos, Alexander J. Stuart

    We explore the implications of recent results relating the Dirac CP-violating phase to predicted and measured leptonic mixing angles within a standard set of theoretical scenarios in which charged lepton corrections are responsible for generating a non-zero value of the reactor mixing angle. We employ a full set of leptonic sum rules as required by the unitarity of the lepton mixing matrix, which can be reduced to predictions for the observable mixing angles and the Dirac CP-violating phase in terms of model parameters. These sum rules are investigated within a given set of theoretical scenarios for the neutrino sector diagonalization matrix for several known classes of charged lepton corrections. The results provide explicit maps of the allowed model parameter space within each given scenario and assumed form of charged lepton perturbations.

  • Jet cross sections and transverse momentum distributions with NNLOJET. (arXiv:1801.06415v1 [hep-ph])

    Authors: T. Gehrmann, X. Chen, J. Cruz-Martinez, J.R. Currie, E.W.N. Glover, T.A. Morgan, J. Niehues, D.M. Walker, R. Gauld, A. Gehrmann-De Ridder, A. Huss, Joao Pires

    This talk discusses recent results for next-to-next-to-leading order (NNLO) QCD corrections to jet cross sections and transverse momentum distributions. The results are obtained in the NNLOJET code framework, which provides an implementation of the antenna subtraction method for the handling of infrared singular contributions at NNLO. We briefly describe the NNLOJET implementation, with particular emphasis on the construction of the real radiation phase space, which is tailored to ensure stability in all infrared sensitive regions.

  • On the convergence of the chiral expansion for the baryon ground-state masses. (arXiv:1801.06417v1 [hep-lat])

    Authors: M.F.M. Lutz, Yonggoo Heo, Xiao-Yu Guo

    We study the chiral expansion of the baryon octet and decuplet masses. It is illustrated that a chiral expansion of the one-loop contributions is rapidly converging up to quark masses that generously encompasses the mass of the physical strange quark. We express the successive orders in terms of physical meson and baryon masses. In addition, owing to specific correlations amongst the chiral moments, we suggest a reordering of terms that make the convergence properties more manifest. Explicit expressions up to chiral order five are derived for all baryon masses at the one-loop level. The baryon masses obtained do not depend on the renormalization scale. The novel chiral ordering is tested against QCD lattice data at N$^3$LO, where the low-energy parameters are systematically correlated by large-$N_c$ sum rules. A reproduction of the baryon masses from PACS-CS, LHPC, HSC, NPLQCD, QCDSF-UKQCD and ETMC is achieved for ensembles with pion and kaon masses smaller than 600 MeV. Predictions for baryon masses on ensembles from CLS as well as all low-energy constants that enter the baryon masses at N$^3$LO are made.

  • Towards analytic local sector subtraction at NNLO. (arXiv:1801.06458v1 [hep-ph])

    Authors: Lorenzo Magnea, Ezio Maina, Paolo Torrielli, Sandro Uccirati

    A new method for local subtraction at next-to-next-to-leading order in QCD is sketched, attempting to conjugate the minimal counterterm structure arising from a sector partition of the radiation phase space with the simplifications following from analytic integration of the counterterms.

  • Factorization and subtraction. (arXiv:1801.06462v1 [hep-ph])

    Authors: Lorenzo Magnea, Ezio Maina, Paolo Torrielli, Sandro Uccirati

    We explore the connection between the factorisation of virtual corrections to multi-particle massless gauge theory amplitudes and the problem of subtraction at NNLO and beyond. Taking inspiration from virtual factorisation, we provide a set of definitions for local soft and collinear counterterms, expressed in terms of matrix elements of operators involving fields and Wilson lines, and valid to all orders in perturbation theory. We hope that the connection between factorisation and subtraction will help in the construction of minimal, stable, and efficient subtraction algorithms, taking maximal advantage of existing analytic information.

  • Model-Independent $\bar\nu_{e}$ Short-Baseline Oscillations from Reactor Spectral Ratios. (arXiv:1801.06467v1 [hep-ph])

    Authors: S. Gariazzo, C. Giunti, M. Laveder, Y.F. Li

    We consider the ratio of the spectra measured in the DANSS neutrino experiment at 12.7 and 10.7~m from a nuclear reactor. These data give a new model-independent indication in favor of short-baseline $\bar\nu_{e}$ oscillations which reinforce the model-independent indication found in the late 2016 in the NEOS experiment. The combined analysis of the NEOS and DANSS spectral ratios in the framework of 3+1 active-sterile neutrino mixing favor short-baseline $\bar\nu_{e}$ oscillations with a statistical significance of $3.7\sigma$. The two mixing parameters $\sin^{2}2\vartheta_{ee}$ and $\Delta{m}^{2}_{41}$ are constrained at $2\sigma$ in a narrow-$\Delta{m}^{2}_{41}$ island at $\Delta{m}^2_{41} \simeq 1.3 \, \text{eV}^2$, with $ \sin^{2}2\vartheta_{ee} = 0.049 \pm 0.023 $ ($2\sigma$). We discuss the implications of the model-independent NEOS+DANSS analysis for the reactor and Gallium anomalies. The NEOS+DANSS model-independent determination of short-baseline $\bar\nu_{e}$ oscillations allows us to analyze the reactor rates without assumptions on the values of the main reactor antineutrino fluxes and the data of the Gallium source experiments with free detector efficiencies. The corrections to the reactor neutrino fluxes and the Gallium detector efficiencies are obtained from the fit of the data. In particular, we confirm the indication in favor of the need for a recalculation of the $^{235}\text{U}$ reactor antineutrino flux found in previous studies assuming the absence of neutrino oscillations.

  • Investigating Local Parity Violation in Heavy-Ion Collisions Using Lambda Helicity. (arXiv:1801.06476v1 [hep-ph])

    Authors: L. Evan Finch, Stephen J. Murray

    We propose the measurement of net $\Lambda$ and $\bar{\Lambda}$ helicity, correlated event-by-event with the magnitude and sign of charge separation along the event's magnetic field direction, as a probe to investigate the Chiral Magnetic Effect in Heavy-Ion Collisions. With a simple simulation model of heavy-ion events that includes effects of Local Parity Violation, we estimate the experimental correlation signal that could be expected at RHIC given the results of previous measurements that are sensitive to the CME.

  • The fate of the Littlest Higgs Model with T-parity under 13 TeV LHC Data. (arXiv:1801.06499v1 [hep-ph])

    Authors: Daniel Dercks, Gudrid Moortgat-Pick, Jurgen Reuter, So Young Shim

    We exploit all LHC available Run 2 data at center-of-mass energies of 8 and 13 TeV for searches for physics beyond the Standard Model. We scrutinize the allowed parameter space of Little Higgs models with the concrete symmetry of T-parity by providing comprehensive analyses of all relevant production channels of heavy vectors, top partners, heavy quarks and heavy leptons and all phenomenologically relevant decay channels. Constraints on the model will be derived from the signatures of jets and missing energy or leptons and missing energy. Besides the symmetric case, we also study the case of T-parity violation. Furthermore, we give an extrapolation to the LHC high-luminosity phase at 14 TeV as well.

  • Top quark modelling in POWHEG BOX. (arXiv:1801.06511v1 [hep-ph])

    Authors: Tomáš Ježo

    We review recent theoretical improvements of Monte Carlo event generators for top-quark pair production and decay at the LHC based on the POWHEG method. We present an event generator that implements spin correlations and off-shell effects in top-decay chains described in terms of exact matrix elements for $pp\to \ell^+\nu_{\ell}\, l^-\bar{\nu}_{l} \,b \,\bar b$ at order $\alpha^4 \alpha_s^2$, including full NLO QCD corrections and interference effects with single-top and non-resonant topologies yielding to the same final state. We then compare its predictions to previous generators that implement NLO corrections only in the top-pair production dynamics. We consider the mass distributions of the $Wj_{\rm B}$ and $\ell j_{\rm B}$ systems, proxies for direct top-mass determinations, and jet-vetoed cross section, a probe of the $Wt$ single top contribution.

  • Compact Perturbative Expressions for Neutrino Oscillations in Matter: II. (arXiv:1801.06514v1 [hep-ph])

    Authors: Peter B. Denton, Hisakazu Minakata, Stephen J. Parke

    In this paper we rewrite the neutrino mixing angles and mass squared differences in matter given, in our original paper, in a notation that is more conventional for the reader. Replacing the usual neutrino mixing angles and mass squared differences in the expressions for the vacuum oscillation probabilities with these matter mixing angles and mass squared differences gives an excellent approximation to the oscillation probabilities in matter. Comparisons for T2K, NOvA, T2HKK and DUNE are also given for neutrinos and anti-neutrinos, disappearance and appearance channels, normal ordering and inverted ordering.

  • Probing the Seesaw Mechanism and Leptogenesis with the International Linear Collider. (arXiv:1801.06534v1 [hep-ph])

    Authors: Stefan Antusch, Eros Cazzato, Marco Drewes, Oliver Fischer, Bjorn Garbrecht, Dario Gueter, Juraj Klaric

    We investigate the potential of the International Linear Collider (ILC) to probe the mechanisms of neutrino mass generation and leptogenesis within the minimal seesaw model. Our results can also be used as an estimate for the potential of a Compact Linear Collider (CLIC). We find that heavy sterile neutrinos that simultaneously explain both, the observed light neutrino oscillations and the baryon asymmetry of the universe, can be found in displaced vertex searches at ILC. We further study the precision at which the flavour-dependent active-sterile mixing angles can be measured. The measurement of the ratios of these mixing angles, and potentially also of the heavy neutrino mass splitting, can test whether minimal type I seesaw models are the origin of the light neutrino masses, and it can be a first step towards probing leptogenesis as the mechanism of baryogenesis. Our results show that the ILC can be used as a discovery machine for New Physics in feebly coupled sectors that can address fundamental questions in particle physics and cosmology.

  • Searches for vector-like quarks at future colliders and implications for composite Higgs models with dark matter. (arXiv:1801.06537v1 [hep-ph])

    Authors: Mikael Chala, Ramona Gröber, Michael Spannowsky

    Many composite Higgs models predict the existence of vector-like quarks with masses outside the reach of the LHC, e.g. $m_Q \gtrsim 2$ TeV, in particular if these models contain a dark matter candidate. In such models the mass of the new resonances is bounded from above to satisfy the constraint from the observed relic density. We therefore develop new strategies to search for vector-like quarks at a future $100$ TeV collider and evaluate what masses and interactions can be probed. We find that masses as large as $\sim 6.4$ ($\sim 9$) TeV can be tested if the fermionic resonances decay into Standard Model (dark matter) particles. We also discuss the complementarity of dark matter searches, showing that most of the parameter space can be closed. On balance, this study motivates further the consideration of a higher-energy hadron collider for a next generation of facilities.

  • A data-driven approach to $\pi^{0}, \eta$ and $\eta^{\prime}$ single and double Dalitz decays. (arXiv:1511.04916v2 [hep-ph] UPDATED)

    Authors: Rafel Escribano, Sergi Gonzàlez-Solís

    The dilepton invariant mass spectra and integrated branching ratios of the single and double Dalitz decays $\mathcal{P}\to\ell^{+}\ell^{-}\gamma$ and $\mathcal{P}\to\ell^{+}\ell^{-}\ell^{+}\ell^{-}$ ($\mathcal{P}=\pi^{0}, \eta, \eta^{\prime}$; $\ell=e$ or $\mu$) are predicted by means of a data-driven approach based on the use of rational approximants applied to $\pi^{0}, \eta$ and $\eta^{\prime}$ transition form factor experimental data in the space-like region.

  • Flavored Gauge Mediation with Discrete Non-Abelian Symmetries. (arXiv:1610.09024v2 [hep-ph] UPDATED)

    Authors: Lisa L. Everett, Todd S. Garon

    We explore the model-building and phenomenology of flavored gauge mediation models of supersymmetry breaking in which the electroweak Higgs doublets and the SU(2) messenger doublets are connected by a discrete non-Abelian symmetry. The embedding of the Higgs and messenger fields into representations of this non-Abelian Higgs-messenger symmetry results in specific relations between the Standard Model Yukawa couplings and the messenger-matter Yukawa interactions. Taking the concrete example of an S(3) Higgs-messenger symmetry, we demonstrate that while the minimal implementation of this scenario suffers from a severe mu/B_mu problem that is well-known from ordinary gauge mediation, expanding the Higgs-messenger field content allows for the possibility that mu and B_mu can be separately tuned, allowing for the possibility of phenomenologically viable models of the soft supersymmetry breaking terms. We construct toy examples of this type that are consistent with the observed 125 GeV Higgs boson mass.

  • Holographic QCD phase diagram with critical point from Einstein-Maxwell-dilaton dynamics. (arXiv:1702.06731v3 [hep-ph] UPDATED)

    Authors: J. Knaute, R. Yaresko, B. Kämpfer

    Supplementing the holographic Einstein-Maxwell-dilaton model of [O. DeWolfe, S.S. Gubser, C. Rosen, Phys. Rev. D83 (2011) 086005; O. DeWolfe, S.S. Gubser, C. Rosen, Phys. Rev. D84 (2011) 126014] by input of lattice QCD data for 2+1 flavors and physical quark masses for the equation of state and quark number susceptibility at zero baryo-chemical potential we explore the resulting phase diagram over the temperature-chemical potential plane. A first-order phase transition sets in at a temperature of about 112 MeV and a baryo-chemical potential of 612 MeV. We estimate the accuracy of the critical point position in the order of approximately 5-8% by considering parameter variations and different low-temperature asymptotics for the second-order quark number susceptibility. The critical pressure as a function of the temperature has a positive slope, i.e. the entropy per baryon jumps up when crossing the phase border line from larger values of temperature/baryo-chemical potential, thus classifying the phase transition as a gas liquid one. The updated holographic model exhibits in- and outgoing isentropes in the vicinity of the first-order phase transition.

  • A tale of two modes: Neutrino free-streaming in the early universe. (arXiv:1704.06657v4 [astro-ph.CO] UPDATED)

    Authors: Lachlan Lancaster, Francis-Yan Cyr-Racine, Lloyd Knox, Zhen Pan

    We present updated constraints on the free-streaming nature of cosmological neutrinos from cosmic microwave background (CMB) power spectra, baryonic acoustic oscillation data, and local measurements of the Hubble constant. Specifically, we consider a Fermi-like four-fermion interaction between massless neutrinos, characterized by an effective coupling constant $ G_{\rm eff}$, and resulting in a neutrino opacity $\dot{\tau}_\nu\propto G_{\rm eff}^2 T_\nu^5$. Using a conservative prior on the parameter $\log_{10}\left(G_{\rm eff} {\rm MeV}^2\right)$, we find a bimodal posterior distribution. The first of these modes is consistent with the standard $\Lambda$CDM cosmology and corresponds to neutrinos decoupling at redshift $z_{\nu,{\rm dec}} > 1.3\times10^5$. The other mode of the posterior, dubbed the "interacting neutrino mode", corresponds to neutrino decoupling occurring within a narrow redshift window centered around $z_{\nu,{\rm dec}}\sim8300$. This mode is characterized by a high value of the effective neutrino coupling constant, together with a lower value of the scalar spectral index and amplitude of fluctuations, and a higher value of the Hubble parameter. Using both a maximum likelihood analysis and the ratio of the two mode's Bayesian evidence, we find the interacting neutrino mode to be statistically disfavored compared to the standard $\Lambda$CDM cosmology. Interestingly, the addition of CMB polarization and direct Hubble constant measurements significantly raises the statistical significance of this secondary mode, indicating that new physics in the neutrino sector could help explain the difference between local measurements of $H_0$, and those inferred from CMB data. A robust consequence of our results is that neutrinos must be free streaming long before the epoch of matter-radiation equality.

  • Discovery potential for directional Dark Matter detection with nuclear emulsions. (arXiv:1705.00613v2 [astro-ph.CO] UPDATED)

    Authors: N. Agafonova, A. Aleksandrov, A. Anokhina, T. Asada, V.V. Ashikhmin, I. Bodnarchuk, A. Buonaura, M. Chernyavskii, A. Chukanov, N. D'Ambrosio, G. De Lellis, A. Di Crescenzo, N. Di Marco, S. Dmitrievski, R.I. Enikeev, R. A. Fini, G. Galati, V. Gentile, S. Gorbunov, Y. Gornushkin, A. M. Guler, H. Ichiki, T. Katsuragawa, N. Konovalova, K. Kuge, A. Lauria, K.Y. Lee, L. Lista, A.S. Malgin, A. Managadze, P. Monacelli, M. C. Montesi, T. Naka, N. Okateva, B.D. Park, D. Podgrudkov, N. Polukhina, F. Pupilli, T. Roganova, A. Rogozhnikov, G. Rosa, O.G. Ryazhskaya, O. Sato, I.R. Shakiryanova, T. Shchedrina, C. Sirignano, J.Y. Sohn, A. Sotnikov, N. Starkov, P. Strolin, V. Tioukov, A. Umemoto, A. Ustyuzhanin, C.S. Yoon, M. Yoshimoto, S. Vasina

    Direct Dark Matter searches are nowadays one of the most fervid research topics with many experimental efforts devoted to the search for nuclear recoils induced by the scattering of Weakly Interactive Massive Particles (WIMPs). Detectors able to reconstruct the direction of the nucleus recoiling against the scattering WIMP are opening a new frontier to possibly extend Dark Matter searches beyond the neutrino background. Exploiting directionality would also prove the galactic origin of Dark Matter with an unambiguous signal-to-background separation. Indeed, the angular distribution of recoiled nuclei is centered around the direction of the Cygnus constellation, while the background distribution is expected to be isotropic. Current directional experiments are based on gas TPC whose sensitivity is limited by the small achievable detector mass. In this paper we present the discovery potential of a directional experiment based on the use of a solid target made of newly developed nuclear emulsions and of optical read-out systems reaching unprecedented nanometric resolution.

  • Higgs Boson Plus Dijets: Higher Order Corrections. (arXiv:1706.01002v3 [hep-ph] UPDATED)

    Authors: Jeppe R. Andersen, Tuomas Hapola, Andreas Maier, Jennifer M. Smillie

    The gluon fusion component of Higgs-boson production in association with dijets is of particular interest because it both (a) allows for a study of the CP-structure of the Higgs-boson couplings to gluons, and (b) provides a background to the otherwise clean study of Higgs-boson production through vector-boson fusion. The degree to which this background can be controlled, and the CP-structure of the gluon-Higgs coupling extracted, both depend on the successful description of the perturbative corrections to the gluon-fusion process.

    High Energy Jets (HEJ) provides all-order, perturbative predictions for multi-jet processes at hadron colliders at a fully exclusive, partonic level. We develop the framework of HEJ to include the process of Higgs-boson production in association with at least two jets. We discuss the logarithmic accuracy obtained in the underlying all-order results, and calculate the first next-to-leading corrections to the framework of HEJ, thereby significantly reducing the corrections which arise by matching to and merging fixed-order results.

    Finally, we compare predictions for relevant observables obtained with NLO and HEJ. We observe that the selection criteria commonly used for isolating the vector-boson fusion component suppresses the gluon-fusion component even further than predicted at NLO.

  • Masses and Mixing of Neutral Leptons in a Grand Unified E_6 Model with Intermediate Pati-Salam Symmetry. (arXiv:1707.03144v2 [hep-ph] UPDATED)

    Authors: Secil Benli, Tekin Dereli

    A brief review of the assignment of elementary fermions and bosons to irreducible multiplets in grand unified $E_6$ models is followed by a discussion of different, hierarchical symmetry breaking chains from $E_6$ down to $SU(3)_C \times U(1)_{EM}$. We concentrate here on a model with an intermediate Pati-Salam symmetry for which $(B-L)$ is conserved. In particular, the mass/mixing matrix of electrically neutral fermions (i.e.neutrinos) that would be derived from Yukawa couplings is constructed. The pattern of neutrino masses and some bounds on mixing parameters are discussed.

  • Attractive vs. repulsive interactions in the Bose-Einstein condensation dynamics of relativistic field theories. (arXiv:1707.07696v2 [hep-ph] UPDATED)

    Authors: J. Berges, K. Boguslavski, A. Chatrchyan, J. Jaeckel

    We study the impact of attractive self-interactions on the nonequilibrium dynamics of relativistic quantum fields with large occupancies at low momenta. Our primary focus is on Bose-Einstein condensation and nonthermal fixed points in such systems. As a model system we consider O(N)-symmetric scalar field theories. We use classical-statistical real-time simulations, as well as a systematic 1/N expansion of the quantum (2PI) effective action to next-to-leading order. When the mean self-interactions are repulsive, condensation occurs as a consequence of a universal inverse particle cascade to the zero-momentum mode with self-similar scaling behavior. For attractive mean self-interactions the inverse cascade is absent and the particle annihilation rate is enhanced compared to the repulsive case, which counteracts the formation of coherent field configurations. For N >= 2, the presence of a nonvanishing conserved charge can suppress number changing processes and lead to the formation of stable localized charge clumps, i.e. Q-balls.

  • Spin-$0^\pm$ portal induced Dark Matter. (arXiv:1709.00720v3 [hep-ph] UPDATED)

    Authors: Sukanta Dutta, Ashok Goyal, Lalit Kumar Saini

    Standard model (SM) spin-zero singlets are constrained through their di-Bosonic decay channels via an effective coupling induced by a vector-like quark (VLQ) loop at the LHC for $\sqrt{s}$ = 13 TeV. These spin-zero resonances are then considered as portals for scalar, vector or fermionic dark matter particle interactions with SM gauge bosons. We find that the model is validated with respect to the observations from LHC data and from cosmology, indirect and direct detection experiments for an appreciable range of scalar, vector and fermionic DM masses greater than 300 GeV and VLQ masses $\ge$ 400 GeV, corresponding to the three choice of portal masses 270 GeV, 500 GeV and 750 GeV respectively.

  • Hyperfine splitting in ordinary and muonic hydrogen. (arXiv:1709.06544v2 [hep-ph] UPDATED)

    Authors: Oleksandr Tomalak

    We provide an accurate evaluation of the two-photon exchange correction to the hyperfine splitting of S energy levels in muonic hydrogen exploiting the corresponding measurements in electronic hydrogen. The proton structure uncertainty in the calculation of $\alpha^5$ contribution is sizably reduced.

  • Transport coefficients in Polyakov quark meson coupling model: a relaxation time approximation. (arXiv:1709.08013v2 [hep-ph] UPDATED)

    Authors: Aman Abhishek, Hiranmaya Mishra, Sabyasachi Ghosh

    We compute the transport coefficients, namely, the coefficients of shear and bulk viscosities as well as thermal conductivity for hot and dense matter. The calculations are performed within the Polyakov quark meson model. The estimation of the transport coefficients is made using the Boltzmann kinetic equation within the relaxation time approximation. The energy dependent relaxation time is estimated from meson meson scattering, quark meson scattering and quark quark scattering within the model. In our calculations, the shear viscosity to entropy ratio and the coefficient of thermal conductivity show a minimum at the critical temperature, while the ratio of bulk viscosity to entropy density exhibits a peak at this transition point.The effect of confinement modelled through a Polyakov loop potential plays an important role in the estimation of these dissipative coefficients both below and above the critical temperature.

  • Future prospects for exploring present day anomalies in flavour physics measurements with Belle II and LHCb. (arXiv:1709.10308v4 [hep-ph] UPDATED)

    Authors: Johannes Albrecht, Florian Bernlochner, Matthew Kenzie, Stefanie Reichert, David Straub, Alison Tully

    A range of flavour physics observables show tensions with their corresponding Standard Model expectations: measurements of leptonic flavour-changing neutral current processes and ratios of semi-leptonic branching fractions involving different generations of leptons show deviations of the order of four standard deviations. If confirmed, either would be an intriguing sign of new physics. In this manuscript, we analyse the current experimental situation of such processes and for the first time estimate the combined impact of the future datasets of the Belle II and LHCb experiments on the present tensions with the Standard Model expectations by performing scans of the new physics contribution to the Wilson coefficients. In addition, the present day and future sensitivity of tree-level CKM parameters, which offer orthogonal tests of the Standard Model, are explored. Three benchmark points in time are chosen for a direct comparison of the estimated sensitivity between the experiments. A high complementarity between the future sensitivity achieved by the Belle II and LHCb experiments is observed due to their relative strengths and weaknesses. We estimate that all of the anomalies considered here will be either confirmed or ruled out by both experiments independently with very high significance by the end of data-taking at Belle II and the LHCb upgrade.

  • On-the-fly reduction of open loops. (arXiv:1710.11452v2 [hep-ph] UPDATED)

    Authors: Federico Buccioni, Stefano Pozzorini, Max Zoller

    Building on the open-loop algorithm we introduce a new method for the automated construction of one-loop amplitudes and their reduction to scalar integrals. The key idea is that the factorisation of one-loop integrands in a product of loop segments makes it possible to perform various operations on-the-fly while constructing the integrand. Reducing the integrand on-the-fly, after each segment multiplication, the construction of loop diagrams and their reduction are unified in a single numerical recursion. In this way we entirely avoid objects with high tensor rank, thereby reducing the complexity of the calculations in a drastic way. Thanks to the on-the-fly approach, which is applied also to helicity summation and for the merging of different diagrams, the speed of the original open-loop algorithm can be further augmented in a very significant way. Moreover, addressing spurious singularities of the employed reduction identities by means of simple expansions in rank-two Gram determinants, we achieve a remarkably high level of numerical stability. These features of the new algorithm, which will be made publicly available in a forthcoming release of the OpenLoops program, are particularly attractive for NLO multi-leg and NNLO real-virtual calculations.

  • Refinements of the Bottom and Strange MSSM Higgs Yukawa Couplings at NNLO. (arXiv:1711.02555v2 [hep-ph] UPDATED)

    Authors: Margherita Ghezzi, Seraina Glaus, Dario Müller, Timo Schmidt, Michael Spira

    We extend the already existing two-loop calculation of the effective bottom-Yukawa coupling in the MSSM. In addition to the resummation of the dominant corrections for large values of tg$\beta$, we include the subleading terms induced by the trilinear Higgs coupling $A_b$. This calculation has been extended to the NNLO corrections to the MSSM strange-Yukawa coupling. Our analysis leads to residual theoretical uncertainties at the per-cent level.

  • Anomaly matching for phase diagram of massless $\mathbb{Z}_N$-QCD. (arXiv:1711.10487v3 [hep-th] UPDATED)

    Authors: Yuya Tanizaki, Yuta Kikuchi, Tatsuhiro Misumi, Norisuke Sakai

    We elucidate that the phase diagram of massless $N$-flavor QCD under $\mathbb{Z}_N$ flavor-twisted boundary condition (massless $\mathbb{Z}_N$-QCD) is constrained by an 't Hooft anomaly involving two-form gauge fields. As a consequence, massless $\mathbb{Z}_N$-QCD turns out to realize persistent order at any temperatures and quark chemical potentials, namely, the symmetric and gapped phase is strictly forbidden. This is the first result on the finite-$(T,\mu)$ phase diagram in QCD-type theories based on anomaly matching related to center and discrete axial symmetries.

  • The Top Mass in Hadronic Collisions. (arXiv:1712.02796v3 [hep-ph] UPDATED)

    Authors: Paolo Nason

    I discuss theoretical issues related to the top mass measurements in hadronic collisions.

  • Tagging Jets in Invisible Higgs Searches. (arXiv:1712.03973v2 [hep-ph] UPDATED)

    Authors: Anke Biekötter, Fabian Keilbach, Rhea Moutafis, Tilman Plehn, Jennifer Thompson

    Searches for invisible Higgs decays in weak boson fusion are a well-known laboratory for jets and QCD studies. We present a series of results on tagging jets and central jet activity. First, precision analyses of the central jet activity require full control of single top production. Second, the rate dependence on the size of the tagging jets is not limited to weak boson fusion. For the first time, we show how subjet information on the tagging jets and on the additional jet activity can be used to extract the Higgs signal. The additional observables relieve some of the pressure on other, critical observables. Finally, we compare the performance of weak boson fusion and associated Higgs production.

  • $[SU(2)]^3$ Dark Matter. (arXiv:1712.08994v3 [hep-ph] UPDATED)

    Authors: Ernest Ma (UC Riverside and HKUST)

    An extra $SU(2)_D$ gauge factor is added to the well-known left-right extension of the standard model (SM) of quarks and leptons. Under $SU(2)_L \times SU(2)_R \times SU(2)_D$, two fermion bidoublets $(2,1,2)$ and $(1,2,2)$ are assumed. The resulting model has an automatic dark $U(1)$ symmetry, in the same way that the SM has automatic baryon and lepton $U(1)$ symmetries. Phenomenological implications are discussed, as well as the possible origin of this proposal.

  • Doubly charmed baryon production in heavy ion collisions. (arXiv:1801.02652v2 [hep-ph] UPDATED)

    Authors: Xiaojun Yao, Berndt Müller

    We give an estimate of $\Xi_{cc}^{++}$ production rate and transverse momentum spectra in relativistic heavy ion collisions. We use Boltzmann transport equations to describe the dynamical evolution of charm quarks and diquarks inside quark-gluon plasma. In-medium formation and dissociation rates of charm diquarks are calculated from potential non-relativistic QCD for the diquark sector. We solve the transport equations by Monte Carlo simulations. For $2.76$ TeV Pb-Pb collisions with $0-10\%$ centrality, the number of $\Xi_{cc}^{++}$ in the transverse momentum range $0-5$ GeV and rapidity from $-1$ to $1$ is roughly $0.026$ per collision. We repeat the calculation with a melting temperature $250$ MeV above which no diquarks can be formed. The number of $\Xi_{cc}^{++}$ produced in the same kinematic region is about $0.016$ per collision. We also discuss extensions to other doubly heavy baryons and doubly heavy tetraquarks.

  • Vector leptoquark mass limits and branching ratios of $ K_L^0, B^0, B_s \to l^+_i l^-_j $ decays with account of fermion mixing in leptoquark currents. (arXiv:1801.02895v2 [hep-ph] UPDATED)

    Authors: A. D. Smirnov

    The contributions of the vector leptoquarks of Pati-Salam type to the branching ratios of $K_L^0, B^0, B_s \to l \, l^{\prime}$ decays are calculated with account of the fermion mixing in the leptoguark currents of the general type. Using the general parametrizations of the mixing matrices the lower vector leptoquark mass limit $ m_V > 86 \,\, TeV $ is found from the current experimental data on these decays. The branching ratios of the decays $B^0, B_s \to l \, l^{\prime}$ predicted at $m_V = 86 \,\, TeV$ are calculated. These branching ratios for the decays $ B^0, B_s \to \mu^+ \mu^-, e \mu $ are close to the experimental data whereas those for the decays $B^0 \to e^+ e^-, e \tau, \mu \tau$, and $B_s \to e^+ e^-$ are by order of $2\div4$ less than their current experimental limits. For the decays $B_s \to e \tau, \mu \tau$ these branching ratios are of order $10^{-10}$ and $10^{-9}$ respectively. The predicted branching ratios will be usefull in the current and future experimental searches for these decays.

  • Prospects for indirect detection of frozen-in dark matter. (arXiv:1801.03089v2 [hep-ph] UPDATED)

    Authors: Matti Heikinheimo, Tommi Tenkanen, Kimmo Tuominen

    We study observational consequences arising from dark matter (DM) of non-thermal origin, produced by dark freeze-out from a hidden sector heat bath. We assume this heat bath was populated by feebly-coupled mediator particles, produced via a Higgs portal interaction with the Standard Model (SM). The dark sector then attained internal equilibrium with a characteristic temperature different from the SM photon temperature. We find that even if the coupling between the DM and the SM sectors is very weak, the scenario allows for indirect observational signals. We show how the expected strength of these signals depends on the temperature of the hidden sector at DM freeze-out.

  • Search for sterile neutrinos decaying into pions at the LHC. (arXiv:1801.03624v2 [hep-ph] UPDATED)

    Authors: Claudio O. Dib, C.S. Kim, Nicolas A. Neill, Xing-Bo Yuan

    We study the possibility to observe sterile neutrinos with masses in the range between 5 GeV and 20 GeV at the LHC, using the exclusive semileptonic modes involving pions, namely W to lepton + N to n pions + lepton+lepton (n = 1, 2, 3). The two pion and three pion modes require extrapolations of form factors to large time-like $q^2$, which we do using vector dominance models as well as light front holographic QCD, with remarkable agreement. This mass region is difficult to explore with inclusive dilepton+dijet modes or trilepton modes and impossible to explore in rare meson decays. While particle identification is a real challenge in these modes, vertex displacement due to the long living neutrino in the above mass range can greatly help reduce backgrounds. Assuming a sample of $10^9$ W bosons at the end of the LHC Run 2, these modes could discover a sterile neutrino in the above mass range or improve the current bounds on the heavy-to-light lepton mixings by an order of magnitude, $U_{l N}^2 \sim 2 \times 10^{-6}$. Moreover, by studying the equal sign and opposite sign dileptons, the Majorana or Dirac character of the sterile neutrino may be revealed.

  • $f(T)$ gravity after GW170817 and GRB170817A. (arXiv:1801.05827v1 [gr-qc] CROSS LISTED)

    Authors: Yi-Fu Cai, Chunlong Li, Emmanuel N. Saridakis, LingQin Xue

    The combined observation of GW170817 and its electromagnetic counterpart GRB170817A reveals that gravitational waves propagate at the speed of light in high precision. We apply the effective field theory approach to investigate the experimental consequences for the theory of $f(T)$ gravity. We find that the speed of gravitational waves within $f(T)$ gravity is exactly equal to the light speed, and hence the constraints from GW170817 and GRB170817A are trivially satisfied. The results are verified through the standard analysis of cosmological perturbations. Nevertheless, by examining the dispersion relation and the frequency of cosmological gravitational waves, we observe a deviation from the results of General Relativity, quantified by a new parameter. Although its value is relatively small in viable $f(T)$ models, its possible future measurement in advancing gravitational-wave astronomy would be the smoking gun of testing this type of modified gravity.

  • Primordial black holes with an accurate QCD equation of state. (arXiv:1801.06138v1 [astro-ph.CO] CROSS LISTED)

    Authors: Christian T. Byrnes, Mark Hindmarsh, Sam Young, Michael R. S. Hawkins

    Making use of definitive new lattice computations of the Standard Model thermodynamics during the quantum chromodynamic (QCD) phase transition, we calculate the enhancement in the mass distribution of primordial black holes (PBHs) due to the softening of the equation of state. We find that the enhancement peaks at approximately $0.7M_\odot$, with the formation rate increasing by at least two orders of magnitude due to the softening of the equation of state at this time, with a range of approximately $0.3M_\odot<M<1.4M_\odot$ at full width half-maximum. PBH formation is increased by a smaller amount for PBHs with masses spanning a large range, $10^{-3}M_\odot<M_{\rm PBH}<10^{3}M_\odot$, which includes the masses of the BHs that LIGO detected. The most significant source of uncertainty in the number of PBHs formed is now due to unknowns in the formation process, rather than from the phase transition. A near scale-invariant density power spectrum tuned to generate a population with mass and merger rate consistent with that detected by LIGO should also produce a much larger energy density of PBHs with solar mass. This solar-mass population could constitute a significant fraction of the cold dark matter density.

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