Thu·Jul 26, 2018Thursday·July 26, 2018

1. 01*

   Neutrino masses and gauged $U(1{)}_{\ell }$ lepton number

   We-Fu Chang🇹🇼 · John N. Ng🇨🇦

   We investigate the tree-level neutrino mass generation in the gauged $U(1{)}_{\ell }$ lepton model recently proposed by us [arXiv:1805.10382]. With the addition of one Standard Model(SM) singlet, ${\varphi }_1(Y=0,\ell =1)$, and one SM triplet scalar, $T(Y=-1,\ell =0)$, realistic lepton masses can be accommodated. The resulting magnitude of neutrino mass is given by $\sim v_t^3/v_L^2$, where $v_t$ and $v_L$ are the vacuum expectation values of $T$ and ${\varphi }_1$, respectively, and it is automatically of the inverse see-saw type. Since $v_L$ is the lepton number violation scale we take it to be high, i.e. $\mathcal{O}\gtrsim (\text{mbox}TeV)$. Moreover, the induced lepton flavor violating processes and the phenomenology of the peculiar triplet are studied. An interesting bound, $0.1\lesssim v_t\lesssim 24.1$ GeV, is obtained when taking into account the neutrino mass generation, $Br(\mu \to e\gamma )$, and the limits from oblique parameters, $\Delta S$ and $\Delta T$. Collider phenomenology of the SM triplets is also discussed.

   hep-phJHEP(2018)·7 citations
2. 02*

   Five-Point Two-Loop Amplitudes from Numerical Unitarity

   Samuel Abreu🇩🇪 · Fernando Febres Cordero🇩🇪 · Harald Ita🇩🇪 · Ben Page🇩🇪 · Mao Zeng🇺🇸

   We present advances in the development of the numerical unitarity method for the computation of multi-loop amplitudes in QCD. As an application, we show results for all the leading-color two-loop five-gluon helicity amplitudes. The amplitudes are reduced to a linear combination of master integrals by employing unitarity-compatible integration-by-parts identities, and the corresponding integral coefficients are computed in an exact manner on rational phase-space points through finite fields arithmetics.

   hep-phhep-thPoS(2018)·8 citations
3. 03*

   Convective stability of global thermodynamic equilibrium

   Wojciech Florkowski🇵🇱 · Avdhesh Kumar🇵🇱 · Radoslaw Ryblewski🇵🇱

   We apply the convection stability criterion to a fluid in global thermodynamic equilibrium with a rigid rotation or with a constant acceleration along the streamlines. Different equations of state describing strongly interacting matter are considered and for each of them the analysed system is found to be stable with respect to convection. This finding brings new evidence for physical relevance of non-static global equilibrium states. Our results can be directly used for other similar media to check their convective stability.

   hep-phnucl-thPRC(2019)·2 citations
4. 04*

   Massive quark form factors

   Roman N. Lee🇷🇺 · Alexander V. Smirnov🇷🇺 · Vladimir A. Smirnov🇷🇺 · Matthias Steinhauser🇩🇪

   In this contribution we provide further details to the recent calculation of QCD corrections to massive three-loop form factors presented in Ref. [1].

   hep-phPoS(2018)·0 citations
5. 05*

   Compact Exotic Tetraquark Mesons in Large-$N_c$ QCD

   Wolfgang Lucha🇦🇹 · Dmitri Melikhov🇦🇹 · Hagop Sazdjian🇫🇷

   We embark on systematic explorations of the behaviour of tetraquark mesons (colour-singlet bound states of two quarks and two antiquarks) in the (idealized) limit of a large number $N_c$ of colour degrees of freedom of quantum chromodynamics. Considering the scattering of two ordinary mesons into two ordinary mesons, we start off with formulating a set of selection criteria that should enable us to unambiguously single out precisely those contributions to all encountered scattering amplitudes that potentially will develop tetraquark poles. Assuming that tetraquark mesons do exist and, if so, emerge in the contributions compatible with our criteria at largest admissible order of $N_c$, we deduce, for the categories of tetraquarks that exhibit either four or only two different open quark flavours, that the decay rates of these tetraquark types are, at least, of order $1/N_c^2$ and that internal consistency requires all the members of the first species to exist pairwise, distinguishable by their favoured two-ordinary-meson decay channels.

   hep-phEPJ Web Conf.(2018)·1 citation
6. 06*

   VBS studies in CMS

   Raquel Gomez-Ambrosio (IPPP, Durham)🇬🇧

   In these proceedings we discuss the family of Vector Boson Scattering (VBS) processes, in particular we look at a very recent result from the CMS collaboration where a search was performed for VBS in the four-lepton and two-jet final state using proton-proton collisions at 13 TeV. The electroweak production of two Z bosons in association with two jets was measured with an observed (expected) significance of 2.7 (1.6) standard deviations, using a multivariate classifier. Additionally an expected significance of 1.2 standard deviations was found using matrix elements techniques. In this work we discuss the latter approach in detail.

   hep-phActa Phys.Polon.Supp.(2018)·9 citations
7. 07*

   LHC Searches for Top-philic Kaluza-Klein Graviton

   Chao-Qiang Geng🇨🇳 · Da Huang🇵🇱 · Kimiko Yamashita🇹🇼

   We study the phenomenology of a massive graviton $G$ with non-universal couplings to the Standard Model (SM) particles. Such a particle can arise as a warped Kaluza-Klein graviton from a framework of the Randall-Sundrum extra-dimension model. In particular, we consider a case in which $G$ is top-philic, i.e., $G$ interacts strongly with the right-handed top quark, resulting in the large top-loop contributions to its production via the gluon fusion and its decays to the SM gauge bosons. We take into account the constraints from the current 13 TeV LHC data on the channels of $t\bar{t}$, $\gamma \gamma$, $jj(gg)$, $\gamma Z$, and $ZZ$. Consequently, it is found that the strongest limit for this spin-2 resonance $G$ comes from the $t\bar{t}$ pair search, which constrains the cutoff scale to be of $\mathcal{O}$(100 GeV) for the right-top coupling of $\mathcal{O}(1)$ and the massive graviton mass in the range $m_G$=2-5 TeV, significantly relaxed compared with the universal $G$ coupling case.

   hep-phhep-exJHEP(2018)·6 citations
8. 08*

   Applications of integrand reduction to two-loop five-point scattering amplitudes in QCD

   Simon Badger🇬🇧 · Christian Brønnum-Hansen🇬🇧 · Thomas Gehrmann🇨🇭 · Heribertus Bayu Hartanto🇬🇧 · Johannes Henn🇩🇪 · Nicola Adriano Lo Presti🇬🇧 · Tiziano Peraro🇩🇪

   We review the current state-of-the-art in integrand level reduction for five-point scattering amplitudes at two loops in QCD. We present some benchmark results for the evaluation of the leading colour two-loop five-gluon amplitudes in the physical region as well as the partonic channels for two quarks and three gluons and four quarks and one gluon.

   hep-phhep-thPoS(2018)·38 citations
9. 09*

   Probing the Higgs self-coupling through double Higgs production in vector boson scattering at the LHC

   E. Arganda🇦🇷 · C. Garcia-Garcia🇪🇸 · M. J. Herrero🇪🇸

   In this work we explore the sensitivity to the Higgs self-coupling $\lambda$ in the production of two Higgs bosons via vector boson scattering at the LHC. Although these production channels, concretely $W^{+}{W}^{-}\to HH$ and $ZZ\to HH$, have lower rates than gluon-gluon fusion, they benefit from being tree level processes, being independent of top physics and having very distinctive kinematics that allow to obtain very clean experimental signatures. This makes them competitive channels concerning the sensitivity to the Higgs self-coupling. In order to give predictions for the sensitivity to this coupling, we first study the role of $\lambda$ at the subprocess level, both in and beyond the Standard Model, to move afterwards to the LHC scenario. We characterize the $pp\to HHjj$ case first and then provide quantitative results for the values of $\lambda$ that can be probed at the LHC in vector boson scattering processes after considering the Higgs boson decays. We focus mainly in $pp\to b\bar{b}b\bar{b}jj$, since it has the largest signal rates, and also comment on the potential of other channels, such as $pp\to b\bar{b}\gamma \gamma jj$, as they lead to cleaner, although smaller, signals. Our whole study is performed for a center of mass energy of $\sqrt{s}=14$ TeV and for various future expected LHC luminosities.

   hep-phNPB(2019)·41 citations
10. 10*

    Radiative quark $p_T$-broadening in a quark-gluon plasma beyond the soft gluon approximation

    B.G. Zakharov🇷🇺

    We study the radiative correction to $p_T$-broadening of a fast quark in a quark-gluon plasma beyond the soft gluon approximation. We find that the radiative processes can suppress considerably $p_T$-broadening. This differs dramatically from previous calculations to logarithmic accuracy in the soft gluon approximation, predicting a considerable enhancement of $p_T$-broadening.

    hep-phnucl-thPisma Zh.Eksp.Teor.Fiz.(2018)·9 citations
11. 11*

    Axion mass prediction from minimal grand unification

    Luca Di Luzio🇬🇧 · Andreas Ringwald🇩🇪 · Carlos Tamarit🇩🇪

    We propose a minimal realization of the Peccei Quinn mechanism in a realistic SU(5) model, where the axion mass is directly connected to the grand-unification scale. By taking into account constraints from proton decay, collider searches and gauge coupling unification, we predict the axion mass: $m_a\in [4.8,6.6]$ neV. The upper bound can be relaxed up to $m_a<330$ neV, at the cost of tuning the flavour structure of the proton decay operators. The predicted mass window will be complementarily probed by the axion dark matter experiments ABRACADABRA and CASPER-Electric, which could provide an indirect evidence for the scale of grand unification before the observation of proton decay.

    hep-phhep-exPRD(2018)·51 citations
12. 12*

    Lightish but clumpy: scalar dark matter from inflationary fluctuations

    Gonzalo Alonso-Álvarez🇩🇪 · Joerg Jaeckel🇩🇪

    It has recently been shown [1] that light vector particles produced from inflationary fluctuations can give rise to the dark matter in the Universe. A similar mechanism has been discussed in [2] for a non-minimally coupled scalar enjoying a Higgs portal interaction. We discuss in detail how such a generation of dark matter works in a minimal setup of a massive scalar non-minimally coupled to gravity. For suitable values of the non-minimal coupling any initial constant value of the field is suppressed during inflation. At the same time, the quantum fluctuations acquired during inflation give rise to a peaked energy density power spectrum. Isocurvature constraints can be avoided since nearly all of the energy is concentrated in fluctuations too small to be observed in the CMB. For masses $\gtrsim \mathrm{eV}$ and sufficiently high inflation scale the energy contained in these fluctuations is sufficient to account for the cold dark matter of the Universe. At small scales ${\ell }_{\mathrm{today}}\sim 10^4\mathrm{km}\sqrt{m/\mathrm{eV}}\sim 10^{-4}\mathrm{AU}\sqrt{m/\mathrm{eV}}$ fluctuations are large and we therefore expect a rather clumpy nature of this form of dark matter.

    hep-phastro-ph.COJCAP(2018)·63 citations
13. 13*

    A clockwork solution to the flavor puzzle

    Rodrigo Alonso🇨🇭 · Adrian Carmona🇩🇪 · Barry M. Dillon🇬🇧 · Jernej F. Kamenik🇸🇮 · Jorge Martin Camalich🇪🇸 · Jure Zupan🇺🇸

    We introduce a set of clockwork models of flavor that can naturally explain the large hierarchies of the Standard Model quark masses and mixing angles. Since the clockwork only contains chains of new vector-like fermions without any other dynamical fields, the flavor constraints allow for relatively light new physics scale. For two benchmarks with gear masses just above 1 TeV, allowed by flavor constraints, we discuss the collider searches and the possible ways of reconstructing gear spectra at the LHC. We also examine the similarities and differences with the other common solutions to the SM flavor puzzle, i.e., with the Froggatt-Nielsen models, where we identify a new {\it clockworked } version, and with the Randall-Sundrum models.

    hep-phJHEP(2018)·56 citations
14. 14*

    Classical Nonrelativistic Effective Field Theory and the Role of Gravitational Interactions

    Joshua Eby🇮🇱 · Kyohei Mukaida🇩🇪 · Masahiro Takimoto🇮🇱 · L. C. R. Wijewardhana🇺🇸 · Masaki Yamada🇺🇸

    Coherent oscillation of axions or axion-like particles may give rise to long-lived clumps, called axion stars, because of the attractive gravitational force or its self-interaction. Such a kind of configuration has been extensively studied in the context of oscillons without the effect of gravity, and its stability can be understood by an approximate conservation of particle number in a non-relativistic effective field theory (EFT). We extend this analysis to the case with gravity to discuss the longevity of axion stars and clarify the EFT expansion scheme in terms of gradient energy and Newton's constant. Our EFT is useful to calculate the axion star configuration and its classical lifetime without any ad hoc assumption. In addition, we derive a simple stability condition against small perturbations. Finally, we discuss the consistency of other non-relativistic effective field theories proposed in the literature.

    hep-phastro-ph.COhep-thPRD(2019)·45 citations
15. 15*

    Lattice QCD and the anomalous magnetic moment of the muon

    Harvey B. Meyer🇩🇪 · Hartmut Wittig🇩🇪

    The anomalous magnetic moment of the muon, a_mu, has been measured with an overall precision of 540 ppb by the E821 experiment at BNL. Since the publication of this result in 2004 there has been a persistent tension of 3.5 standard deviations with the theoretical prediction of a_mu based on the Standard Model. The uncertainty of the latter is dominated by the effects of the strong interaction, notably the hadronic vacuum polarisation (HVP) and the hadronic light-by-light (HLbL) scattering contributions, which are commonly evaluated using a data-driven approach and hadronic models, respectively. Given that the discrepancy between theory and experiment is currently one of the most intriguing hints for a possible failure of the Standard Model, it is of paramount importance to determine both the HVP and HLbL contributions from first principles. In this review we present the status of lattice QCD calculations of the leading-order HVP and the HLbL scattering contributions, a_mu^hvp and a_mu^hlbl. After describing the formalism to express a_mu^hvp and a_mu^hlbl in terms of Euclidean correlation functions that can be computed on the lattice, we focus on the systematic effects that must be controlled to achieve a first-principles determination of the dominant strong interaction contributions to a_mu with the desired level of precision. We also present an overview of current lattice QCD results for a_mu^hvp and a_mu^hlbl, as well as related quantities such as the transition form factor for pi0 -> gamma*gamma*. While the total error of current lattice QCD estimates of a_mu^hvp has reached the few-percent level, it must be further reduced by a factor 5 to be competitive with the data-driven dispersive approach. At the same time, there has been good progress towards the determination of a_mu^hlbl with an uncertainty at the 10-15%-level.

    ↳ hep-lathep-phPPNP(2019)·81 citations
16. 16*

    Singularities of plane gravitational waves and their memory effects

    Tongzheng Wang · Jared Fier🇺🇸 · Bowen Li🇺🇸 · Guoliang Lv · Zhaojun Wang · Yumei Wu🇨🇳 · Anzhong Wang

    Similar to the Schwarzschild coordinates for spherical black holes, the Baldwin, Jeffery and Rosen (BJR) coordinates for plane gravitational waves are often singular, and extensions beyond such singularities are necessary, before studying asymptotic properties of such spacetimes at the null infinity of the plane, on which the gravitational waves propagate. The latter is closely related to the studies of memory effects and soft graviton theorems. In this paper, we point out that in the BJR coordinates all the spacetimes are singular physically at the focused point $u=u_s$, except for the two cases: (1) $\alpha =1/2,\forall {\chi }_n$; and (2) $\alpha =1,{\chi }_i=0(i=1,2,3)$, where ${\chi }_n$ are the coefficients in the expansion $\chi \equiv {\left[\text{mbox}det\left(g_{ab}\right)\right]}^{1/4}={\left(u-u_s\right)}^{\alpha }{\sum }_{n=0}^{\infty }{\chi }_n{\left(u-u_s\right)}^n$ with ${\chi }_0\ne 0$, the constant $\alpha \in (0,1]$ characterizes the strength of the singularities, and $g_{ab}$ denotes the reduced metric on the two-dimensional plane orthogonal to the propagation direction of the wave. Therefore, the hypersurfaces $u=u_s$ already represent the boundaries of such spacetimes, and the null infinity does not belong to them. As a result, they cannot be used to study properties of plane gravitational waves at null infinities, including memory effects and soft graviton theorems.

    ↳ gr-qcastro-ph.COhep-phhep-thGen.Rel.Grav.(2020)·9 citations
17. 17*

    Evolution of magnetic fields from the 3+1 dimensional self-similar and Gubser flows in ideal relativistic magnetohydrodynamics

    M. Shokri🇮🇷 · N. Sadooghi🇮🇷

    Motivated by the recently found realization of the $1+1$ dimensional Bjorken flow in ideal and nonideal relativistic magnetohydrodynamics (MHD), we use appropriate symmetry arguments, and determine the evolution of magnetic fields arising from the $3+1$ dimensional self-similar and Gubser flows in an infinitely conductive relativistic fluid (ideal MHD). In the case of the $3+1$ dimensional self-similar flow, we arrive at a family of solutions, that are related through a differential equation arising from the corresponding Euler equation. To find the magnetic field evolution from the Gubser flow, we solve the MHD equations of a stationary fluid in a conformally flat $d{S}^3\times E^1$ spacetime. The results are then Weyl transformed back into the Minkowski spacetime. In this case, the temporal evolution of the resulting magnetic field is shown to exhibit a transition between an early time $1/t$ decay to a $1/t^3$ decay at a late time. Here, $t$ is the time coordinate. Transverse and longitudinal components of the magnetic fields arising from these flows are also found. The latter turns out to be sensitive to the transverse size of the fluid. In contrast to the result arising from the Gubser flow, the radial domain of validity of the magnetic field arising from the self-similar flow is highly restricted. A comparison of the results suggests that the (conformal) Gubser MHD may give a more appropriate qualitative picture of the magnetic field decay in the plasma of quarks and gluons created in heavy ion collisions.

    ↳ nucl-thhep-phhep-thJHEP(2018)·27 citations
18. 18*

    Taiji Program: Gravitational-Wave Sources

    Wen-Hong Ruan🇨🇳 · Zong-Kuan Guo🇨🇳 · Rong-Gen Cai🇨🇳 · Yuan-Zhong Zhang🇨🇳

    We review potential low-frequency gravitational-wave sources, which are expected to be detected by Taiji, a Chinese space-based gravitational-wave detector, estimate the detection rates of these gravitational-wave sources and present the parameter estimation of massive black hole binaries.

    ↳ gr-qchep-phhep-thInt.J.Mod.Phys.A(2020)·799 citations
19. 19*

    Ultra-High-Energy Cosmic Rays

    Luis A. Anchordoqui🇺🇸

    In this report we review the important progress made in recent years towards understanding the experimental data on ultra-high-energy ($E\gtrsim 10^9$ GeV) cosmic rays. We begin with a general survey of the available data, including a description of the energy spectrum, the nuclear composition, and the distribution of arrival directions. At this point we also give a synopsis of experimental techniques. After that, we introduce the fundamentals of cosmic ray acceleration and energy loss during propagation, with a view of discussing the conjectured nearby sources. Next, we survey the state of the art regarding the high- and ultra-high-energy cosmic neutrinos which may be produced in association with the observed cosmic rays. These neutrinos could constitute key messengers identifying currently unknown cosmic accelerators, possibly in the distant universe, because their propagation is not influenced by background photon or magnetic fields. Subsequently, we summarize the phenomenology of cosmic ray air showers. We describe the hadronic interaction models used to extrapolate results from collider data to ultra-high energies and the main electromagnetic processes that govern the longitudinal shower evolution. Armed with these two principal shower ingredients and motivation from the underlying physics, we describe the different methods proposed to distinguish the primary particle species. In the end, we explore how ultra-high-energy cosmic rays can be used as probes of beyond standard model physics models.

    ↳ astro-ph.HEhep-phPhys.Rept.(2019)·244 citations
20. 20*

    New constraints on classical de Sitter: flirting with the swampland

    David Andriot🇨🇭

    We study the existence and stability of classical de Sitter solutions of type II supergravities with parallel Dp-branes and orientifold Op-planes. Together with the dilaton and volume scalar fields, we consider a third one that distinguishes between parallel and transverse directions to the Dp/Op. We derive the complete scalar potential for these three fields. This formalism allows us to reproduce known constraints obtained in 10d, and to derive new ones. Specifying to group manifolds with constant fluxes, we exclude a large region of parameter space, forbidding de Sitter solutions on nilmanifolds, semi-simple group manifolds, and some solvmanifolds. In the small remaining region, we identify a stability island, where the three scalars could be stabilized in any de Sitter solution. We discuss these results in the swampland context.

    ↳ hep-thastro-ph.COgr-qchep-phFortsch.Phys.(2019)·110 citations
21. 21*

    De Sitter and Anti-de Sitter branes in self-tuning models

    Jewel Kumar Ghosh🇫🇷 · Elias Kiritsis🇬🇷 · Francesco Nitti🇫🇷 · Lukas T. Witkowski🇫🇷

    Maximally symmetric curved-brane solutions are studied in dilatonic braneworld models which realise the self-tuning of the effective four-dimensional cosmological constant. It is found that no vacua in which the brane has de Sitter or anti-de Sitter geometry exist, unless one modifies the near-boundary asymptotics of the bulk fields. In the holographic dual picture, this corresponds to coupling the UV CFT to a curved metric (possibly with a defect). Alternatively, the same may be achieved in a flat-space QFT with suitable variable scalar sources. With these ingredients, it is found that maximally symmetric, positive and negative curvature solutions with a stabilised brane position generically exist. The space of such solutions is studied in two different types of realisations of the self-tuning framework. In some regimes we observe a large hierarchy between the curvature on the brane and the boundary UV CFT curvature. This is a dynamical effect due to the self-stabilisation mechanism. This setup provides an alternative route to realising de Sitter space in string theory.

    ↳ hep-thgr-qchep-phJHEP(2018)·25 citations
22. 22*

    Lattice Boltzmann study of the one-dimensional boost-invariant expansion with anisotropic initial conditions

    Victor E. Ambrus🇷🇴 · Calin Guga-Rosian🇷🇴

    A numerical algorithm for the implementation of anisotropic distributions in the frame of the relativistic Boltzmann equation is presented. The implementation relies on the expansion of the Romatschke-Strickland distribution with respect to orthogonal polynomials, which is evolved using the lattice Boltzmann algorithm. The validation of our proposed scheme is performed in the context of the one-dimensional boost invariant expansion (Bjorken flow) at various values of the ratio $\eta /s$ of the shear viscosity to the entropy density. This study is limited to the case of massless particles obeying Maxwell-Jüttner statistics.

    ↳ nucl-thhep-phAIP Conf.Proc.(2019)·3 citations
23. 23*

    Bimagnetic Monopoles

    D. Bazeia🇧🇷 · M.A. Marques🇧🇷 · R. Menezes🇧🇷

    Motivated by recent results on small and hollow magnetic monopoles and on core and shell bimagnetic nanoparticles, we propose the construction of bimagnetic monopoles, which are structures that accommodate a magnetic monopole inside another magnetic monopole.

    ↳ hep-thcond-mat.supr-conhep-phphysics.class-phPRD(2018)·7 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.