Tue·Aug 1, 2017Tuesday·August 1, 2017

1. 01*

   A $\mathrm{U}(2)\times \mathrm{U}(3)$ gauge theory extension of the standard model

   Rafael Herrera🇲🇽 · Alexander Quintero Velez🇨🇴

   We consider an extension of the standard model based on the group $\mathrm{U}(2)\times \mathrm{U}(3)$, which is naturally compatible with the standard model interacting-particle representations and the spontaneous symmetry breaking of $\mathrm{U}(2)\times \mathrm{U}(3)$ to an electrostrong $\mathrm{U}(3)$. In its minimal version, the model only adds one extra $\mathrm{U}(1)$ gauge boson and it implies that the hypercharge is distributed between the factors of the hyperweak and hyperstrong forces. We show that the anomaly cancellation condition can be solved by adding exotic fermions associated with a $16$-dimensional representation of $\mathrm{U}(2)\times \mathrm{U}(3)$. A brief discussion of the mechanism of the spontaneous breakdown of $\mathrm{U}(2)\times \mathrm{U}(3)$ in the gauge boson sector is given.

   hep-phhep-thmath.RTJ.Geom.Phys.(2019)·0 citations
2. 02*

   Charm Quark Mass with Calibrated Uncertainty

   Jens Erler🇲🇽 · Pere Masjuan🇪🇸 · Hubert Spiesberger🇩🇪

   We determine the charm quark mass ${\hat{m}}_c({\hat{m}}_c)$ from QCD sum rules of moments of the vector current correlator calculated in perturbative QCD. Only experimental data for the charm resonances below the continuum threshold are needed in our approach, while the continuum contribution is determined by requiring self-consistency between various sum rules, including the one for the zeroth moment. Existing data from the continuum region can then be used to bound the theoretical error. Our result is ${\hat{m}}_c({\hat{m}}_c)=1272\pm 8$ MeV for ${\hat{\alpha }}_s(M_Z)=0.1182$. Special attention is given to the question how to quantify and justify the uncertainty.

   hep-phPoS(2017)·0 citations
3. 03*

   Neutron stars at the dark matter direct detection frontier

   Nirmal Raj🇺🇸 · Philip Tanedo🇺🇸 · Hai-Bo Yu🇺🇸

   Neutron stars capture dark matter efficiently. The kinetic energy transferred during capture heats old neutron stars in the local galactic halo to temperatures detectable by upcoming infrared telescopes. We derive the sensitivity of this probe in the framework of effective operators. For dark matter heavier than a GeV, we find that neutron star heating can set limits on the effective operator cutoff that are orders of magnitude stronger than possible from terrestrial direct detection experiments in the case of spin-dependent and velocity-suppressed scattering.

   hep-phastro-ph.HEastro-ph.IMhep-exPRD(2018)·158 citations
4. 04*

   Parapositronium can decay into three photons

   Andrzej Pokraka🇨🇦 · Andrzej Czarnecki🇨🇦

   We calculate the decay rate and spectrum for the decay of parapositronium into three photons. This process violates charge conjugation symmetry. It is forbidden within quantum electrodynamics but proceeds through the weak interaction. The branching ratio we find is fifty orders of magnitude smaller than the previous estimate.

   hep-phhep-thPRD(2017)·23 citations
5. 05*

   $R(D^{\ast })$, $|V_{cb}|$, and the Heavy Quark Symmetry relations between form factors

   Dante Bigi🇮🇹 · Paolo Gambino🇮🇹 · Stefan Schacht🇩🇪

   Stringent relations between the $B^{(\ast )}\to D^{(\ast )}$ form factors exist in the heavy quark limit and the leading symmetry breaking corrections are known. We reconsider their uncertainty and role in the analysis of recent Belle data for $B\to D^{(\ast )}\ell \nu$ with model-independent parametrizations and in the related prediction of $R(D^{(\ast )})$. We find $|V_{cb}|=41.5(1.3)10^{-3}$ and $|V_{cb}|=40.6{(}_{-1.3}^{+1.2})10^{-3}$ using input from Light Cone Sum Rules, and $R(D^{\ast })=0.260(8)$.

   hep-phJHEP(2017)·309 citations
6. 06*

   Revisiting the Equation of State of Hybrid Stars in the Dyson-Schwinger Equation Approach to QCD

   Zhan Bai🇨🇳 · Huan Chen🇮🇹 · Yu-xin Liu🇨🇳

   We investigate the equation of state(EoS) and the effect of the hadron-quark phase transition of strong interaction matter in compact stars. The hadron matter is described with the relativistic mean field theory,and the quark matter is described with the Dyson-Schwinger equation approach of QCD. The complete EoS of the hybrid star matter is constructed with not only the Gibbs construction but also the 3-window interpolation. The mass-radius relation of hybrid stars is also investigated. We find that, although the EoSs of both the hadron matter with hyperon and $\Delta$-baryon and the quark matter are generally softer than that of the nucleon matter, the 3-window interpolation construction may provide an EoS stiff enough for a hybrid star with mass exceeding 2$M_{\odot }^{}$ and, in turn, solve the so called "hyperon puzzle".

   hep-phastro-ph.HEnucl-thPRD(2018)·24 citations
7. 07*

   Heavy-quark symmetry implies stable heavy tetraquark mesons $Q_i{Q}_j{\bar{q}}_k{\bar{q}}_l$

   Estia J. Eichten🇺🇸 · Chris Quigg🇺🇸

   For very heavy quarks $Q$, relations derived from heavy-quark symmetry predict the existence of novel narrow doubly heavy tetraquark states of the form $Q_i{Q}_j{\bar{q}}_k{\bar{q}}_l$ (subscripts label flavors), where $q$ designates a light quark. By evaluating finite-mass corrections, we predict that double-beauty states composed of $bb\bar{u}\bar{d}$, $bb\bar{u}\bar{s}$, and $bb\bar{d}\bar{s}$ will be stable against strong decays, whereas the double-charm states $cc{\bar{q}}_k{\bar{q}}_l$, mixed beauty+charm states $bc{\bar{q}}_k{\bar{q}}_l$, and heavier $bb{\bar{q}}_k{\bar{q}}_l$ states will dissociate into pairs of heavy-light mesons. Observation of a new double-beauty state through its weak decays would establish the existence of tetraquarks and illuminate the role of heavy color-antitriplet diquarks as hadron constituents.

   hep-phhep-exPRL(2017)·330 citations
8. 08*

   Nonperturbative partonic quasidistributions of the pion from chiral quark models

   Wojciech Broniowski🇵🇱 · Enrique Ruiz Arriola🇪🇸

   We evaluate nonperturbatively the quark quasidistribution amplitude and the valence quark quasidistribution function of the pion in the framework of chiral quark models, namely the Nambu--Jona-Lasinio model and the Spectral Quark Model. We arrive at simple analytic expressions, where the nonperturbative dependence on the longitudinal momentum of the pion can be explicitly assessed. The model results for the quark quasidistribution amplitude of the pion compare favorably to the data obtained from the Euclidean lattice simulations. The quark distribution amplitude, arising in the limit of infinite longitudinal momentum of the pion, agrees, after suitable QCD evolution, to the recent data extracted from Euclidean lattices, as well as to the old data from transverse lattice simulations.

   hep-phhep-latPLB(2017)·54 citations
9. 09*

   Magnetic and quadrupole moments of the $Z_c(3900)$

   U. Ozdem🇹🇷 · K. Azizi🇹🇷

   The electromagnetic properties of the tetraquark state $Z_c(3900)$ are investigated in the diquark-antidiquark picture and its magnetic and quadrupole moments are extracted. To this end, the light-cone QCD sum rule in electromagnetic background field is used. The magnetic and quadrupole moments encode the spatial distributions of the charge and magnetization in the particle. The result obtained for the magnetic moment is quite large and can be measured in future experiments. We obtain a nonzero but small value for the quadrupole moment of $Zc(3900)$ indicating a nonspherical charge distribution.

   hep-phPRD(2017)·32 citations
10. 10*

    The Bose-Einstein Correlations and the strong coupling constant at low energies

    G. Alexander (Tel Aviv University)🇮🇱 · B. Blok (Technion)🇮🇱

    It is shown that ${\alpha }_s(E)$, the strong coupling constant, can be determined in the non-perturbative regime from Bose-Einstein correlations (BEC). The obtained ${\alpha }_s(E)$ is in agreement with the prescriptions dealt with in the Analytic Perturbative Theory approach. It also extrapolates smoothly to the standard perturbative ${\alpha }_s(E)$ at higher energies. Our results indicate that BEC dimension can be considered as an alternative approach to the short range measure between hadrons.

    hep-phhep-exnucl-exMDPI Physics(2019)·0 citations
11. 11*

    Sneutrino DM in the NMSSM with inverse seesaw mechanism

    Junjie Cao🇨🇳 · Xiaofei Guo🇨🇳 · Yangle He🇨🇳 · Liangliang Shang🇨🇳 · Yuanfang Yue🇨🇳

    In supersymmetric theories like the Next-to-Minimal Supersymmetric Standard Model (NMSSM), the lightest neutralino with bino or singlino as its dominant component is customarily taken as dark matter (DM) candidate. Since light Higgsinos favored by naturalness can strength the couplings of the DM and thus enhance the DM-nucleon scattering rate, the tension between naturalness and DM direct detection results becomes more and more acute with the improved experimental sensitivity. In this work, we extend the NMSSM by inverse seesaw mechanism to generate neutrino mass, and show that in certain parameter space the lightest sneutrino may act as a viable DM candidate, i.e. it can annihilate by multi-channels to get correct relic density and meanwhile satisfy all experimental constraints. The most striking feature of the extension is that the DM-nucleon scattering rate can be naturally below its current experimental bounds regardless of the higgsino mass, and hence it alleviates the tension between naturalness and DM experiments. Other interesting features include that the Higgs phenomenology becomes much richer than that of the original NMSSM due to the relaxed constraints from DM physics and also due to the presence of extra neutrinos, and that the signatures of sparticles at colliders are quite different from those with neutralino as DM candidate.

    hep-phJHEP(2017)·21 citations
12. 12*

    Constraining Spacetime Nonmetricity with Neutron Spin Rotation in Liquid He-4

    Ralf Lehnert🇺🇸 · W.M. Snow🇺🇸 · Zhi Xiao🇺🇸 · Rui Xu🇺🇸

    General spacetime nonmetricity coupled to neutrons is studied. In this context, it is shown that certain nonmetricity components can generate a rotation of the neutron's spin. Available data on this effect obtained from slow-neutron propagation in liquid helium are used to constrain isotropic nonmetricity components at the level of $10^{-22}$GeV. These results represent the first limit on the nonmetricity ${\zeta }_2^{(6)}{S}_{000}$ parameter as well as the first measurement of nonmetricity inside matter.

    hep-phPLB(2017)·30 citations
13. 13*

    The Born-Oppenheimer approximation in an effective field theory language

    Nora Brambilla🇩🇪 · Gastão Krein🇧🇷 · Jaume Tarrús Castellà🇩🇪 · Antonio Vairo🇩🇪

    The Born--Oppenheimer approximation is the standard tool for the study of molecular systems. It is founded on the observation that the energy scale of the electron dynamics in a molecule is larger than that of the nuclei. A very similar physical picture can be used to describe QCD states containing heavy quarks as well as light-quarks or gluonic excitations. In this work, we derive the Born--Oppenheimer approximation for QED molecular systems in an effective field theory framework by sequentially integrating out degrees of freedom living at energies above the typical energy scale where the dynamics of the heavy degrees of freedom occurs. In particular, we compute the matching coefficients of the effective field theory for the case of the $H_2^{+}$ diatomic molecule that are relevant to compute its spectrum up to $\mathcal{O}(m{\alpha }^5)$. Ultrasoft photon loops contribute at this order, being ultimately responsible for the molecular Lamb shift. In the effective field theory the scaling of all the operators is homogeneous, which facilitates the determination of all the relevant contributions, an observation that may become useful for high-precision calculations. Using the above case as a guidance, we construct under some conditions an effective field theory for QCD states formed by a color-octet heavy quark-antiquark pair bound with a color-octet light-quark pair or excited gluonic state, highlighting the similarities and differences between the QED and QCD systems. Assuming that the multipole expansion is applicable, we construct the heavy-quark potential up to next-to-leading order in the multipole expansion in terms of nonperturbative matching coefficients to be obtained from lattice QCD.

    hep-phnucl-thphysics.atom-phPRD(2018)·101 citations
14. 14*

    Chiral Lagrangians with $\Delta (1232)$ to one loop

    Shao-Zhou Jiang🇨🇳 · Yan-Rui Liu🇨🇳 · Hong-Qian Wang🇨🇳

    We construct the Lorentz-invariant chiral Lagrangians up to the order $\mathcal{O}(p^4)$ by including $\Delta (1232)$ as an explicit degree of freedom. A full one-loop investigation on processes involving $\Delta (1232)$ can be performed with them. For the $\pi \Delta \Delta$ Lagrangian, one obtains 38 independent terms at the order $\mathcal{O}(p^3)$ and 318 independent terms at the order $\mathcal{O}(p^4)$. For the $\pi N\Delta$ Lagrangian, we get 33 independent terms at the order $\mathcal{O}(p^3)$ and 218 independent terms at the order $\mathcal{O}(p^4)$. The heavy baryon projection is also briefly discussed.

    hep-phhep-latnucl-thPRD(2018)·13 citations
15. 15*

    Is There a Sign of New Physics in Beryllium Transitions?

    Bartosz Fornal🇺🇸

    We discuss the current status of the anomaly in beryllium-8 nuclear transitions recently reported in the angular distribution of internal conversion electron-positron pairs. We present a phenomenological analysis of the signal and review the models proposed to explain it, focusing on those involving a new light protophobic vector gauge boson. We also elaborate on the prospects of verifying the anomaly in present and future experiments.

    hep-phInt.J.Mod.Phys.A(2017)·35 citations
16. 16*

    Gravitational Wave Imprint of New Symmetry Breaking

    Wei Chao🇨🇳 · Wen-Feng Cui🇨🇳 · Huai-Ke Guo🇺🇸 · Jing Shu🇨🇳

    It is believed that there are extra fundamental gauge symmetries beyond these described by the Standard Model of particle physics. The scale of these new gauge symmetries are usually too high to be reachable by particle colliders. Considering that the phase transition (PT) relating to the spontaneous breaking of new gauge symmetries to the electroweak symmetry might be strongly first order, we propose in this paper taking the stochastic gravitational waves (GW) arising from this phase transition as an indirect way of detecting these new fundamental gauge symmetries. As an illustration, we explore the possibility of detecting the stochastic GW generated from the PT of $\mathbf{B}-\mathbf{L}$ in the space-based interferometer detectors. Out study shows that the GW energy spectrum is reachable by the LISA, BBO, Taiji and DECIGO experiments only for the case where the spontaneous breaking of $\mathbf{B}-\mathbf{L}$ is triggered by at least two electroweak singlet scalars.

    hep-phCPC(2020)·52 citations
17. 17*

    Analysis of the scalar doubly charmed hexaquark state with QCD sum rules

    Zhi-Gang Wang🇨🇳

    In this article, we study the scalar-diquark-scalar-diquark-scalar-diquark type hexaquark state with the QCD sum rules by carrying out the operator product expansion up to the vacuum condensates of dimension 16. We obtain the lowest hexaquark mass $6.60_{-0.09}^{+0.12}\mathrm{GeV}$, which can be confronted to the experimental data in the future.

    hep-phEPJC(2017)·23 citations
18. 18*

    Systematic Study of One-Loop Dirac Neutrino Masses and Viable Dark Matter Candidates

    Chang-Yuan Yao🇨🇳 · Gui-Jun Ding🇨🇳

    We study the generation of small neutrino masses from the dimension six effective operator at tree level and one-loop level, the neutrinos are assumed to be Dirac particles. We find out all possible tree and one-loop diagrams which lead to finite neutrino masses. The relevant mediator fields and the predictions for neutrino masses are presented. The lower order contributions to neutrino masses can be forbidden by introducing soft breaking abelian symmetry or finite non-abelian symmetry. The messengers inside the loop can be dark matter particles. The possible dark matter candidates and the corresponding constraints on the parameter $\alpha$ are analyzed for each model.

    hep-phPRD(2017)·50 citations
19. 19*

    Renormalization scheme dependence of high-Order perturbative QCD predictions

    Yang Ma🇺🇸 · Xing-Gang Wu🇨🇳

    Conventionally, one adopts typical momentum flow of a physical observable as the renormalization scale for its perturbative QCD (pQCD) approximant. This simple treatment leads to renormalization scheme-and-scale ambiguities due to the renormalization scheme and scale dependence of the strong coupling and the perturbative coefficients do not exactly cancel at any fixed order. It is believed that those ambiguities will be softened by including more higher-order terms. In the paper, to show how the renormalization scheme dependence changes when more loop terms have been included, we discuss the sensitivity of pQCD prediction on the scheme parameters by using the scheme-dependent $\{{\beta }_{m\ge 2}\}$-terms. We adopt two four-loop examples, $e^{+}{e}^{-}\to \mathrm{hadrons}$ and $\tau$ decays into hadrons, for detailed analysis. Our results show that under the conventional scale setting, by including more-and-more loop terms, the scheme dependence of the pQCD prediction cannot be reduced as efficiently as that of the scale dependence. Thus a proper scale-setting approach should be important to reduce the scheme dependence. We observe that the principle of minimum sensitivity could be such a scale-setting approach, which provides a practical way to achieve optimal scheme and scale by requiring the pQCD approximate be independent to the "unphysical" theoretical conventions.

    hep-phPRD(2018)·8 citations
20. 20*

    Standard Model with a Complex Scalar Singlet: Cosmological Implications and Theoretical Considerations

    Cheng-Wei Chiang🇹🇼 · Michael J. Ramsey-Musolf🇺🇸 · Eibun Senaha🇹🇼

    We analyze the theoretical and phenomenological considerations for the electroweak phase transition and dark matter in an extension of the Standard Model with a complex scalar singlet (cxSM). In contrast with earlier studies, we use a renormalization group improved scalar potential and treat its thermal history in a gauge invariant manner. We find that the parameter space consistent with a strong first order electroweak phase transition (SFOEWPT) and present dark matter phenomenological constraints is significantly restricted compared to results of a conventional, gauge non-invariant analysis. In the simplest variant of the cxSM, recent LUX data and a SFOEWPT require a dark matter mass close to half the mass of the Standard Model-like Higgs boson. We also comment on various caveats regarding the perturbative treatment of the phase transition dynamics.

    hep-phPRD(2018)·147 citations
21. 21*

    Anomalous non-conservation of fermion/chiral number in Abelian gauge theories at finite temperature

    Daniel G. Figueroa🇨🇭 · Mikhail Shaposhnikov🇨🇭

    We discuss the non-conservation of fermion number (or chirality breaking, depending on the fermionic charge assignment) in Abelian gauge theories at finite temperature. We study different mechanisms of fermionic charge disappearance in the high temperature plasma, using both analytical estimates and real-time classical lattice numerical simulations. We investigate the random walk of the Chern-Simons number $Q\propto \int d^{4}x{F}_{\mu \nu }{\tilde{F}}^{\mu \nu }$, and show that it has a diffusive behaviour in the presence of an external magnetic field $B$. This indicates that the mechanism for fermionic number non-conservation for $B\ne 0$, is due to fluctuations of the gauge fields, similarly as in the case of non-Abelian gauge theories. We determine numerically, with lattice simulations, the rate $\Gamma$ of chirality non-conservation associated with this diffusion. We find the rate to be a factor $\mathcal{O}(10)$ larger compared to previous theoretical estimates, what calls for a revision of the implications of Abelian fermion number and chirality non-conservation for baryogenesis, magnetogenesis and chiral symmetry evolution. An erratum can be found at the end of the manuscript, following the results obtained in JHEP 10 (2019) 142 (1904.11892 [hep-th]), which reduce our original claim in the discrepancy between theory and numerics by a factor $\sim 5-6$.

    hep-phastro-ph.COhep-lathep-thJHEP(2018)·32 citations
22. 22*

    Predictions for Cold Nuclear Matter Effects in $p+$Pb Collisions at $\sqrt{s_{{}_{NN}}}=8.16$ TeV

    J. L. Albacete🇪🇸 · F. Arleo🇫🇷 · G. G. Barnaföldi🇭🇺 · G. Bíró🇭🇺 · D. d'Enterria🇨🇭 · B. Ducloué🇫🇮 · K. J. Eskola🇫🇮 · E. G. Ferreiro🇪🇸 · M. Gyulassy🇺🇸 · S. M. Harangozó🇭🇺 · I. Helenius🇩🇪 · Z.-B. Kang🇺🇸 and 30 other authors

    Predictions for cold nuclear matter effects on charged hadrons, identified light hadrons, quarkonium and heavy flavor hadrons, Drell-Yan dileptons, jets, photons, gauge bosons and top quarks produced in $p+$Pb collisions at $\sqrt{s_{{}_{NN}}}=8.16$ TeV are compiled and, where possible, compared to each other. Predictions of the normalized ratios of $p+$Pb to $p+p$ cross sections are also presented for most of the observables, providing new insights into the expected role of cold nuclear matter effects. In particular, the role of nuclear parton distribution functions on particle production can now be probed over a wider range of phase space than ever before.

    hep-phNPA(2018)·85 citations
23. 23*

    Extraction of $|V_{cb}|$ from $B\to D^{(\ast )}\ell {\nu }_{\ell }$ and the Standard Model predictions of $R(D^{(\ast )})$

    Sneha Jaiswal🇮🇳 · Soumitra Nandi🇮🇳 · Sunando Kumar Patra🇮🇳

    We extract $|V_{cb}|$ from the available data in the decay $B\to D^{(\ast )}\ell {\nu }_{\ell }$. Our analysis uses the $q^2(w)$ binned differential decay rates in different subsamples of $B\to D\ell {\nu }_{\ell }$ ($\ell =e,\mu$), while for the decay $B\to D^{\ast }\ell {\nu }_{\ell }$, the unfolded binned differential decay rates of four kinematic variables including the $q^2$ bins have been used. In the CLN and BGL parameterizations of the form factors, the combined fit to all the available data along with their correlations yields $|V_{cb}|=(39.77\pm 0.89)\times 10^{-3}$ and $(40.90\pm 0.94)\times 10^{-3}$ respectively. In these fits, we have used the inputs from lattice and light cone sum rule (LCSR) along with the data. Using our fit results and the HQET relations (with the known corrections included) amongst the form factors, and parameterizing the unknown higher order corrections (in the ratios of HQET form factors) with a conservative estimate of the normalizing parameters, we obtain $R(D^{\ast })=0.259\pm 0.006$ (CLN) and $R(D^{\ast })=0.257\pm 0.005$ (BGL).

    hep-phhep-exJHEP(2017)·283 citations
24. 24*

    Little composite dark matter

    Reuven Balkin🇩🇪 · Gilad Perez🇮🇱 · Andreas Weiler🇩🇪

    We examine the dark matter phenomenology of a composite electroweak singlet state. This singlet belongs to the Goldstone sector of a well-motivated extension of the Littlest Higgs with $T$-parity. A viable parameter space, consistent with the observed dark matter relic abundance as well as with the various collider, electroweak precision and dark matter direct detection experimental constraints is found for this scenario. $T$-parity implies a rich LHC phenomenology, which forms an interesting interplay between conventional natural SUSY type of signals involving third generation quarks and missing energy, from stop-like particle production and decay, and composite Higgs type of signals involving third generation quarks associated with Higgs and electroweak gauge boson, from vector-like top-partners production and decay. The composite features of the dark matter phenomenology allows the composite singlet the produce the correct relic abundance while interacting weakly with the Higgs via the usual Higgs portal coupling ${\lambda }_{\text{DM}}\sim O(1\%)$, thus evading direct detection.

    hep-phastro-ph.COEPJC(2018)·28 citations
25. 25*

    Precise predictions for the angular coefficients in Z-boson production at the LHC

    R. Gauld🇨🇭 · A. Gehrmann-De Ridder🇨🇭 · T. Gehrmann🇨🇭 · E.W.N. Glover🇬🇧 · A. Huss🇨🇭

    The angular distributions of lepton pairs in the Drell-Yan process can provide rich information on the underlying QCD production mechanisms. These dynamics can be parameterised in terms of a set of frame dependent angular coefficients, $A_{i=0,\dots ,7}$, which depend on the invariant mass, transverse momentum, and rapidity of the lepton pair. Motivated by recent measurements of these coefficients by ATLAS and CMS, and in particular by the apparent violation of the Lam-Tung relation $A_0-A_2=0$, we perform a precision study of the angular coefficients at $\mathcal{O}({\alpha }_s^3)$ in perturbative QCD. We make predictions relevant for $pp$ collisions at $\sqrt{s}=8$ TeV, and perform comparisons with the available ATLAS and CMS data as well as providing predictions for a prospective measurement at LHCb. To expose the violation of the Lam-Tung relationship we propose a new observable ${\Delta }^{\mathrm{LT}}=1-A_2/A_0$ that is more sensitive to the dynamics in the region where $A_0$ and $A_2$ are both small. We find that the $\mathcal{O}({\alpha }_s^3)$ corrections have an important impact on the $p_{T,Z}$ distributions for several of the angular coefficients, and are essential to provide an adequate description of the data. The compatibility of the available ATLAS and CMS data is reassessed by performing a partial ${\chi }^2$ test with respect to the central theoretical prediction which shows that ${\chi }^2/N_{\mathrm{data}}$ is significantly reduced by going from $\mathcal{O}({\alpha }_s^2)$ to $\mathcal{O}({\alpha }_s^3)$.

    hep-phhep-exJHEP(2017)·94 citations
26. 26*

    Relaxion: A Landscape Without Anthropics

    Ann Nelson🇺🇸 · Chanda Prescod-Weinstein🇺🇸

    The relaxion mechanism provides a potentially elegant solution to the hierarchy problem without resorting to anthropic or other fine-tuning arguments. This mechanism introduces an axion-like field, dubbed the relaxion, whose expectation value determines the electroweak hierarchy as well as the QCD strong CP violating $\bar{\theta }$ parameter. During an inflationary period, the Higgs mass squared is selected to be negative and hierarchically small in a theory which is consistent with 't Hooft's technical naturalness criteria. However, in the original model proposed by Graham, Kaplan and Rajendran (2015), the relaxion does not solve the strong CP problem, and in fact contributes to it, as the coupling of the relaxion to the Higgs field and the introduction of a linear potential for the relaxion produces large strong CP violation. We resolve this tension by considering inflation with a Hubble scale which is above the QCD scale but below the weak scale, and estimating the Hubble temperature dependence of the axion mass. The relaxion potential is thus very different during inflation than it is today. We find that provided the inflationary Hubble scale is between the weak scale and about 3 GeV, the relaxion resolves the hierarchy, strong CP, and dark matter problems in a way that is technically natural.

    hep-phastro-ph.COhep-thPRD(2017)·32 citations
27. 27*

    New signals for vector-like down-type quark in $U(1)$ of $E_6$

    Kasinath Das🇮🇳 · Tianjun Li🇨🇳 · S. Nandi🇺🇸 · Santosh Kumar Rai🇮🇳

    We consider the pair production of vector-like down-type quarks in an $E_6$ motivated model, where each of the produced down-type vector-like quark decays into an ordinary Standard Model light quark and a singlet scalar. Both the vector-like quark and singlet scalar appear naturally in the $E_6$ model with masses at the TeV scale with a favorable choice of symmetry breaking pattern. We focus on the non-standard decay of the vector-like quark and the new scalar which decays to two photons or two gluons. We analyze the signal for the vector-like quark production in the $2\gamma +\ge 2j$ channel and show how the scalar and vector-like quark masses can be determined at the Large Hadron Collider.

    hep-phhep-exEPJC(2018)·12 citations
28. 28*

    Jet-medium interaction and conformal relativistic fluid dynamics

    Li Yan🇨🇦 · Sangyong Jeon🇨🇦 · Charles Gale🇨🇦

    A formalism to study the mode-by-mode response to the energy deposition of external hard partons propagating in a relativistic fluid is developed, based on a semi-analytical solution of conformal fluid-dynamics. The soft particle production resulting from the jet-medium interaction is calculated and the recoil of the viscous medium is studied for different orientations of the relativistic jets, and for different values of the specific shear viscosity $\eta /s$.

    ↳ nucl-thhep-phnucl-exPRC(2018)·32 citations
29. 29*

    UHECR primary identification using the lateral profile of muons in EAS

    Moon Moon Devi🇮🇱 · Ranny Budnik🇮🇱

    New developments in detector technology allow for a realistic cost of large area surface detectors for cosmic ray air showers, with some limitations on particle identification, energy resolutions, directional information and dynamic range. In this paper, we present a simulation study using CORSIKA to quantify the lateral profile of the muons at ground level, characterized by their energy spectrum and lateral spread, and combine it with the depth at shower maximum (X${}_{max}$) of an EAS initiated by a primary at energies $10^{16}$ eV - $10^{19}$ eV. Using different primaries, we show that the combined muon observables and X${}_{max}$ can identify the primary in a large fraction of the events, depending on the energy and the detector performance. This study provides important input parameters for the design of a future muon detector for surface array, which will be able to boost the knowledge of primaries and of the QCD interactions in the atmosphere.

    ↳ astro-ph.IMastro-ph.HEhep-exhep-ph0 citations
30. 30*

    Non-critical fluctuations of (net) charges and (net) protons from iEBE-VISHNU hybrid model

    Jixing Li🇨🇳 · Hao-jie Xu🇨🇳 · Huichao Song🇺🇸

    In this paper, we investigate the non-critical fluctuations of (net) charges and (net) protons in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 39 and 200 GeV, using iEBE-VISHNU hybrid model with Poisson fluctuations added in the particle event generator between hydrodynamics and UrQMD. Various effects, such as volume fluctuations hadronic evolution and scatterings, resonance decays, as well as realistic centrality cuts and acceptance cuts have been embedded in our model calculations. With properly tuned parameters, iEBE-VISHNU roughly describe the centrality dependent moments and cumulants of (net) charges and (net) protons measured in experiment. Further comparison simulations show that the volume fluctuation is the dominant factor to influence the multiplicity fluctuations, which makes the higher moments of (net) charges largely deviate from the Poison baselines. We also find that the effects from hadronic evolutions and resonance decays are pretty small or even negligible for the multiplicity fluctuations of both (net) charges and (net) protons.

    ↳ nucl-thhep-phnucl-exPRC(2018)·22 citations
31. 31*

    Inflationary magnetogenesis with added helicity: constraints from non-gaussianities

    Chiara Caprini🇫🇷 · Maria Chiara Guzzetti🇮🇹 · Lorenzo Sorbo🇺🇸

    In previous work, two of us have proposed a model of inflationary magnetogenesis based on a rolling auxiliary field able both to account for the magnetic fields inferred by the (non) observation of gamma-rays from blazars, and to start the galactic dynamo, without incurring in any strong coupling or strong backreaction regime. Here we evaluate the correction to the scalar spectrum and bispectrum with respect to single-field slow-roll inflation generated in that scenario. The strongest constraints on the model originate from the non-observation of a scalar bispectrum. Nevertheless, even when those constraints are taken into consideration, the scenario can successfully account for the observed magnetic fields as long as the energy scale of inflation is smaller than $10^6÷10^8$~GeV, under some conditions on the slow roll of the auxiliary scalar field.

    ↳ astro-ph.COhep-phClass.Quant.Grav.(2018)·51 citations
32. 32*

    Lattice Quantum Monte Carlo Study of Chiral Magnetic Effect in Dirac Semimetals

    D.L. Boyda🇷🇺 · V.V. Braguta🇷🇺 · M.I. Katsnelson🇳🇱 · A.Yu. Kotov🇷🇺

    In this paper Chiral Magnetic Effect (CME) in Dirac semimetals is studied by means of lattice Monte Carlo simulation. We measure conductivity of Dirac semimetals as a function of external magnetic field in parallel ${\sigma }_{\parallel }$ and perpendicular ${\sigma }_{\perp }$ to the external field directions. The simulations are carried out in three regimes: semimetal phase, onset of the insulator phase and deep in the insulator phase. In the semimetal phase ${\sigma }_{\parallel }$ grows whereas ${\sigma }_{\perp }$ drops with magnetic field. Similar behaviour was observed in the onset of the insulator phase but conductivity is smaller and its dependence on magnetic field is weaker. Finally in the insulator phase conductivities ${\sigma }_{\parallel ,\perp }$ are close to zero and do not depend on magnetic field. In other words, we observe manifestation of the CME current in the semimetal phase, weaker manifestation of the CME in the onset of the insulator phase. We do not observe signatures of CME in the insulator phase. We believe that the suppression of the CME current in the insulator phase is connected to chiral symmetry breaking and generation of dynamical fermion mass which take place in this phase.

    ↳ cond-mat.str-elhep-lathep-phhep-th+1Annals Phys.(2018)·10 citations
33. 33*

    Gravitational Waves from Oscillons with Cuspy Potentials

    Jing Liu🇨🇳 · Zong-Kuan Guo🇨🇳 · Rong-Gen Cai🇨🇳 · Gary Shiu🇺🇸

    We study the production of gravitational waves during oscillations of the inflaton around the minimum of a cuspy potential after inflation. We find that a cusp in the potential can trigger copious oscillon formation, which sources a characteristic energy spectrum of gravitational waves with double peaks. The discovery of such a double-peak spectrum could test the underlying inflationary physics.

    ↳ astro-ph.COgr-qchep-phhep-thPRL(2018)·92 citations
34. 34*

    Higgs amplitudes from $\mathcal{N}=4$ super Yang-Mills theory

    Andreas Brandhuber🇬🇧 · Martyna Kostacinska🇬🇧 · Brenda Penante🇨🇭 · Gabriele Travaglini🇬🇧

    Higgs plus multi-gluon amplitudes in QCD can be computed in an effective Lagrangian description. In the infinite top-mass limit, an amplitude with a Higgs and $n$ gluons is computed by the form factor of the operator $\mathrm{Tr}{F}^2$. Up to two loops and for three gluons, its maximally transcendental part is captured entirely by the form factor of the protected stress tensor multiplet operator ${\mathcal{T}}_2$ in $\mathcal{N}=4$ supersymmetric Yang-Mills theory. The next order correction involves the calculation of the form factor of the higher-dimensional, trilinear operator $\mathrm{Tr}{F}^3$. We present explicit results at two loops for three gluons, including the subleading transcendental terms derived from a particular descendant of the Konishi operator that contains $\mathrm{Tr}{F}^3$. These are expressed in terms of a few universal building blocks already identified in earlier calculations. We show that the maximally transcendental part of this quantity, computed in non-supersymmetric Yang-Mills theory, is identical to the form factor of another protected operator, ${\mathcal{T}}_3$, in the maximally supersymmetric theory. Our results suggest that the maximally transcendental part of Higgs amplitudes in QCD can be entirely computed through $\mathcal{N}=4$ super Yang-Mills.

    ↳ hep-thhep-phPRL(2017)·48 citations
35. 35*

    Subaru Telescope limits on cosmological variations in the fine-structure constant

    Michael T. Murphy (1)🇦🇺 · Kathy L. Cooksey (2) ((1) Swinburne University of Technology, (2) University of Hawaii at Hilo)🇺🇸

    Previous, large samples of quasar absorption spectra have indicated some evidence for relative variations in the fine-structure constant ($\Delta \alpha /\alpha$) across the sky. However, they were likely affected by long-range distortions of the wavelength calibration, so it is important to establish a statistical sample of more reliable results, from multiple telescopes. Here we triple the sample of $\Delta \alpha /\alpha$ measurements from the Subaru Telescope which have been `supercalibrated' to correct for long-range distortions. A blinded analysis of the metallic ions in 6 intervening absorption systems in two Subaru quasar spectra provides no evidence for $\alpha$ variation, with a weighted mean of $\Delta \alpha /\alpha =3.0\pm 2.8_{\mathrm{stat}}\pm 2.0_{\mathrm{sys}}$ parts per million (1$\sigma$ statistical and systematic uncertainties). The main remaining systematic effects are uncertainties in the long-range distortion corrections, absorption profile models, and errors from redispersing multiple quasar exposures onto a common wavelength grid. The results also assume that terrestrial isotopic abundances prevail in the absorbers; assuming only the dominant terrestrial isotope is present significantly lowers $\Delta \alpha /\alpha$, though it is still consistent with zero. Given the location of the two quasars on the sky, our results do not support the evidence for spatial $\alpha$ variation, especially when combined with the 21 other recent measurements which were corrected for, or resistant to, long-range distortions. Our spectra and absorption profile fits are publicly available.

    ↳ astro-ph.COastro-ph.GAgr-qchep-ph+1MNRAS(2017)·50 citations
36. 36*

    Lyman-alpha Constraints on Ultralight Scalar Dark Matter: Implications for the Early and Late Universe

    Takeshi Kobayashi🇮🇹 · Riccardo Murgia🇮🇹 · Andrea De Simone🇮🇹 · Vid Iršič🇺🇸 · Matteo Viel🇮🇹

    We investigate constraints on scalar dark matter (DM) by analyzing the Lyman-alpha forest, which probes structure formation at medium and small scales, and also by studying its cosmological consequences at high and low redshift. For scalar DM that constitutes more than 30% of the total DM density, we obtain a lower limit m >~ 10^{-21} eV for the mass of scalar DM. This implies an upper limit on the initial field displacement (or the decay constant for an axion-like field) of phi <~ 10^{16} GeV. We also derive limits on the energy scale of cosmic inflation and establish an upper bound on the tensor-to-scalar ratio of r < 10^{-3} in the presence of scalar DM. Furthermore, we show that there is very little room for ultralight scalar DM to solve the "small-scale crisis" of cold DM without spoiling the Lyman-alpha forest results. The constraints presented in this paper can be used for testing generic theories that contain light scalar fields.

    ↳ astro-ph.COhep-phhep-thPRD(2017)·299 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.