Thu·Mar 5, 2020Thursday·March 5, 2020

1. 01*

   Nonlinear Compton scattering of polarised photons in plane-wave backgrounds

   B. King🇬🇧 · S. Tang🇬🇧

   We investigate the phenomenology of nonlinear Compton scattering of polarised photons by unpolarised electrons in plane-wave backgrounds. The energy and angular spectra of polarised photons are calculated for linearly- and circularly-polarised pulses, monochromatic fields and constant crossed field backgrounds. When the field intensity is in the weakly nonlinear regime, photons in different polarisation states are predicted to possess very different energy and angular distributions. We explain this difference by calculating the spectrum for nonlinear Thomson scattering in a linearly-polarised monochromatic background and projecting the electron's trajectory onto the different polarisation directions. Finally, we calculate a scenario for multi-GeV electrons and by considering the energy and angular-resolved photon polarisation purity, find one can achieve a GeV-photon beam with polarisation purities of over $90\%$.

   hep-phphysics.opticsquant-phPRA(2020)·54 citations
2. 02*

   Higgs portal to dark matter and $B\to K^{(\ast )}$ decays

   Aliaksei Kachanovich🇩🇪 · Ulrich Nierste🇩🇪 · Ivan Nišandžić🇩🇪

   We consider a Higgs portal model in which the 125-GeV Higgs boson mixes with a light singlet mediator $h_2$ coupling to particles of a Dark Sector and study potential $b\to s{h}_2$ decays in the Belle II experiment. Multiplying the gauge-dependent off-shell Standard-Model $b$-$s$-Higgs vertex with the sine of the Higgs mixing angle does not give the correct $b$-$s$-$h_2$ vertex. We clarify this issue by calculating the $b$-$s$-$h_2$ vertex in an arbitrary $R_{\xi }$ gauge and demonstrate how the $\xi$ dependence cancels from physical decay rates involving an on-shell or off-shell $h_2$. Then we revisit the $b\to s{h}_2$ phenomenology and point out that a simultaneous study of $B\to K^{\ast }{h}_2$ and $B\to K{h}_2$ helps to discriminate between the Higgs portal and alternative models of the Dark Sector. We further advocate for the use of the $h_2$ lifetime information contained in displaced-vertex data with $h_2$ decaying back to Standard-Model particles to better constrain the $h_2$ mass or to reveal additional $h_2$ decay modes into long-lived particles.

   hep-phEPJC(2020)·35 citations
3. 03*

   Probing single stop production at the FCC-hh/SPPC

   Tian-Peng Tang🇨🇳 · Hang Zhou🇨🇳 · Ning Liu🇨🇳

   Top squark (stop) is a crucial part of supersymmetric models (SUSY) to understand the naturalness problem. Other than the traditional stop pair production, the single production via electroweak interaction provides signals with distinctive features which could help confirm the existence of the top squark. In this paper, we investigate the observability of stop through the mono-top channel of the single stop production at the future proton-proton colliders, FCC-hh and SPPC, in a simplified Minimal Supersymmetric Standard Model (MSSM). With the integrated luminosity of 3000 ${\text{fb}}^{-1}$, we can probe the stop with mass up to 3.25 TeV by the mono-top channel at $5\sigma$ level. Considering the systematic uncertainty of 10%, the exclusion limit for stop mass can be reached at about 1.5 TeV. Exclusion limits on stop mass and higgsino mass parameter $\mu$ are also presented.

   hep-phNPB(2020)·1 citation
4. 04*

   A search for axion-like particles in light-by-light scattering at the CLIC

   S.C. Inan🇹🇷 · A.V. Kisselev🇷🇺

   The virtual production of axion-like particles (ALPs) in the light-by-light scattering at the CLIC collider is studied. Both differential and total cross sections are calculated, assuming interaction of the ALP with photons via CP-odd term in the Lagrangian. The 95\% C.L. exclusion regions for the ALP mass and its coupling constant are given. By comparing our results with existing collider bounds, we see that the ALP search at the CLIC has a great physics potential of searching for the ALPs, especially, in the mass region 1 TeV -- 2.4 TeV, with the collision energy $\sqrt{s}=3000$ GeV and integrated luminosity $L=5000$ fb${}^{-1}$ for the Compton backscattered initial photons. In particular, our limits are stronger that recently obtained bounds for the ALP production in the light-by-light scattering at the LHC.

   hep-phhep-exJHEP(2020)·29 citations
5. 05*

   Quenching of light hadron spectra in pA collisions from fully coherent energy loss

   François Arleo🇫🇷 · Stéphane Peigné🇫🇷

   We single out the role of fully coherent induced gluon radiation on light hadron production in pA collisions. The effect has an interesting color structure, as the induced radiation depends on the global color charge of the partonic subprocess final state. Baseline predictions for light hadron nuclear suppression in pPb collisions at the LHC are provided, taking into account only the effect of fully coherent energy loss, which proves of the same order of magnitude as gluon shadowing or saturation. This underlines the need to include fully coherent energy loss in phenomenological studies of hadron production in pA collisions.

   hep-phPRL(2020)·15 citations
6. 06*

   Thermo-magnetic spectral properties of neutral mesons in vector and axial-vector channels using NJL model

   Snigdha Ghosh🇮🇳 · Arghya Mukherjee🇮🇳 · Nilanjan Chaudhuri🇮🇳 · Pradip Roy🇮🇳 · Sourav Sarkar🇮🇳

   In this work the neutral meson properties have been investigated in the presence of thermo-magnetic background using two-flavor Nambu--Jona-Lasinio model. Mass, spectral function and dispersion relations are obtained in the scalar ($\sigma$) and pseudo-scalar (${\pi }^0$) channels as well as in the vector (${\rho }^0$) and axial vector ($a_1^0$) channels. The general Lorentz structures for the vector and axial-vector meson polarization functions have been considered in detail. The ultra-violet divergences appearing in this work have been regularized using a mixed regularization technique where the gamma functions arising in dimensional regularization are replaced with incomplete gamma functions as usually done in the proper time regularization procedure. The meson spectral functions obtained in the presence of a magnetic field possess nontrivial oscillatory structure. Similar to the scalar and pseudo-scalar channel, the spectral functions for each of the modes of ${\rho }^0$ are observed to overlap with the corresponding modes of its chiral partner $a_1^0$ mesons in the chiral symmetry restored phase. We observe discontinuities in the masses of all the mesonic excitations for a non-zero external magnetic field.

   hep-phnucl-thPRD(2020)·30 citations
7. 07*

   The Violation of Equivalence Principle and Four Neutrino Oscillations for Long Baseline Neutrinos

   Madhurima Pandey🇮🇳 · Debasish Majumdar🇮🇳 · Amit Dutta Banik🇨🇳 · Ashadul Halder🇮🇳

   Violation of equivalence principle predicts that neutrinos of different flavor couple differently with gravity. Such a scenario can give rise to gravity induced flavor oscillations in addition to the usual mass flavor neutrino oscillations during the neutrino propagation. Even if the equivalence principle is indeed violated, their measure will be extremely small. We explore the possibility to probe the violation of equivalence principle (VEP) for the case of long baseline (LBL) neutrinos in a 4-flavor neutrino framework (3 active + 1 sterile) where both mass and gravity induced oscillations are considered. To this end, we have explicitly calculated the oscillation probability in 4-flavor framework that includes in addition to the mass-flavor mixing in matter, the gravity-flavor mixing also. The energy eigenvalues are then obtained by diagonalizing such a 4-flavor mixing matrix. The formalism is then employed to estimate the wrong and right sign muon yields at a far detector for neutrinos produced in a neutrino factory and travel through the Earth matter. These results are compared with the similar estimations when the usual three active neutrinos are considered.

   hep-phMod.Phys.Lett.A(2021)·6 citations
8. 08*

   Dark origins of matter-antimatter asymmetry

   Venus Keus🇫🇮

   In a non-minimal Higgs framework, we present a novel mechanism in which the CP violating dark particles only interact with the SM through the gauge bosons, primarily the $Z$ boson. Such $Z$-portal dark CP violation is realised in the regions of the parameter space where Higgs-mediated (co)annihilation processes are sub-dominant and have negligible contributions to the DM relic density. We show that such $Z$-portal CP violating DM can still thermalise and satisfy all experimental and observational bounds and discuss implications of such phenomena for electroweak baryogenesis.

   hep-phastro-ph.COPoS(2020)·8 citations
9. 09*

   Leptophobic $Z^{\prime }$ in supersymmetry and where to find them

   Jack Y. Araz🇨🇦

   This report presents possible loopholes in heavy $Z^{\prime }$ searches which are concentrated around high mass resonances. We present a scenario where massive neutral vector boson $Z^{\prime }$, predicted by $E_6$-inspired $U(1{)}^{\prime }$ models, can become leptophobic due to kinetic mixing between $Z-Z^{\prime }$. Such a scenario can avoid high-mass dilepton resonance searches. Furthermore, we propose a channel through supersymmetric cascade decays to observe leptophobic $Z^{\prime }$. We show that it is possible to reach up to $8\sigma$ at $\sqrt{s}=14$ TeV and 3 ab${}^{-1}$ integrated luminosity. This report follows the steps of the work that has been conducted in ref. [arXiv:1711.06302].

   hep-ph"Quantum Theory and Symmetries", edited b…·0 citations
10. 10*

    A Quantum Algorithm for Model-Independent Searches for New Physics

    Konstantin T. Matchev🇺🇸 · Prasanth Shyamsundar🇺🇸 · Jordan Smolinsky🇺🇸

    We propose a novel quantum technique to search for unmodeled anomalies in multidimensional binned collider data. We propose associating an Ising lattice spin site with each bin, with the Ising Hamiltonian suitably constructed from the observed data and a corresponding theoretical expectation. In order to capture spatially correlated anomalies in the data, we introduce spin-spin interactions between neighboring sites, as well as self-interactions. The ground state energy of the resulting Ising Hamiltonian can be used as a new test statistic, which can be computed either classically or via adiabatic quantum optimization. We demonstrate that our test statistic outperforms some of the most commonly used goodness-of-fit tests. The new approach greatly reduces the look-elsewhere effect by exploiting the typical differences between statistical noise and genuine new physics signals.

    hep-phhep-exphysics.data-anquant-phLHEP(2023)·14 citations
11. 11*

    Towards stability of NLO corrections in High-Energy Factorization via Modified Multi-Regge Kinematics approximation

    Maxim Nefedov🇷🇺

    The perturbatively-stable scheme of Next-to-Leading order (NLO) calculations of cross-sections for multi-scale hard-processes in DIS-like kinematics is developed in the framework of High-Energy Factorization. The evolution equation for unintegrated PDF, which resums $\log 1/z$-corrections to the coefficient function in the Leading Logarithmic approximation together with a certain subset of Next-to-Leading Logarithmic and Next-to-Leading Power corrections, necessary for the perturbative stability of the formalism, is formulated and solved in the Doubly-Logarithmic approximation. An example of DIS-like process, induced by the operator $\mathrm{tr}\left[G_{\mu \nu }{G}^{\mu \nu }\right]$, which is sensitive to gluon PDF already in the LO, is studied. Moderate ($O(20\%)$) NLO corrections to the inclusive structure function are found at small $x_B<10^{-4}$, while for the $p_T$-spectrum of a leading jet in the considered process, NLO corrections are small ($<O(20\%)$) and LO of $k_T$-factorization is a good approximation. The approach can be straightforwardly extended to the case of multi-scale hard processes in $pp$-collisions at high energies.

    hep-phJHEP(2020)·28 citations
12. 12*

    Can we fit our nuclear PDFs with the high-$x$ CLAS data?

    Hannu Paukkunen🇫🇮 · Pia Zurita🇩🇪

    Nuclear parton distribution functions (nuclear PDFs) are non-perturbative objects that encode the partonic behaviour of bound nucleons. To avoid potential higher-twist contributions, the data probing the high-$x$ end of nuclear PDFs are sometimes left out from the global extractions despite their potential to constrain the fit parameters. In the present work we focus on the kinematic corner covered by the new high-$x$ data measured by the CLAS/JLab collaboration. By using the Hessian re-weighting technique, we are able to quantitatively test the compatibility of these data with globally analyzed nuclear PDFs and explore the expected impact on the valence-quark distributions at high $x$. We find that the data are in a good agreement with the EPPS16 and nCTEQ15 nuclear PDFs whereas they disagree with TuJu19. The implications on flavour separation, higher-twist contributions and models of EMC effect are discussed.

    hep-phEPJC(2020)·14 citations
13. 13*

    Invisible Axion Search Methods

    Pierre Sikivie🇺🇸

    In the late 1970's, the axion was proposed as a solution to the Strong CP Problem, i.e. the puzzle why the strong interactions conserve parity P and the product CP of charge conjugation and parity in spite of the fact that the Standard Model of elementary particles as a whole violates those symmetries. The original axion was soon ruled out by laboratory experiments and astrophysical considerations, but a new version was invented which is much more weakly coupled and which evades the laboratory and astrophysical constraints. It was dubbed the invisible" axion. However, the axion cannot be arbitrarily weakly coupled because it is overproduced in the early universe by vacuum realignment in the limit of vanishing coupling. The axions produced by vacuum realignment are a form of cold dark matter today. The axion provides a solution then not only to the Strong CP Problem but also to the dark matter problem. Various methods have been proposed to search for dark matter axions and for axions emitted by the Sun. Their implementation and improvement has led to significant constraints on the notion of an invisible axion. Even purely laboratory methods may place significant constraints on invisible axions or axion-like particles. This review discusses the various methods that have been proposed and provides theoretical derivations of their signals.

    hep-phRMP(2021)·439 citations
14. 14*

    Electron-positron annihilation into two photons in an intense plane-wave field

    S. Bragin🇩🇪 · A. Di Piazza🇩🇪

    The process of electron-positron annihilation into two photons in the presence of an intense classical plane wave of an arbitrary shape is investigated analytically by employing light-cone quantization and by taking into account the effects of the plane wave exactly. We introduce a general description of second-order 2-to-2 scattering processes in a plane-wave background field, indicating the necessity of considering the localization of the colliding particles and achieving that by means of wave packets. We define a local cross section in the background field, which generalizes the vacuum cross section and which, though not being directly an observable, allows for a comparison between the results in the plane wave and in vacuum without relying on the shape of the incoming wave packets. Two possible cascade or two-step channels have been identified in the annihilation process and an alternative way of representing the two-step and one-step contributions via a "virtuality" integral has been found. Finally, we compute the total local cross section to leading order in the coupling between the electron-positron field and the quantized photon field, excluding the interference between the two leading-order diagrams arising from the exchange of the two final photons, and express it in a relatively compact form. In contrast to processes in a background field initiated by a single particle, the pair annihilation into two photons, in fact, also occurs in vacuum. Our result naturally embeds the vacuum part and reduces to the vacuum expression, known in the literature, in the case of a vanishing laser field.

    hep-phPRD(2020)·22 citations
15. 15*

    Expanding the parameter space of natural supersymmetry

    Amin Aboubrahim🇺🇸 · Wan-Zhe Feng🇨🇳 · Pran Nath🇺🇸

    SUSY/SUGRA models with naturalness defined via small $\mu$ are constrained due to experiment on the relic density and the experimental limits on the WIMP-proton cross-section and WIMP annihilation cross-section from indirect detection experiments. Specifically models with small $\mu$ where the neutralino is higgsino-like lead to dark matter relic density below the observed value. In several works this problem is overcome by assuming dark matter to be constituted of more than one component and the neutralino relic density deficit is made up from contributions from other components. In this work we propose that the dark matter consists of just one component, i.e., the lightest neutralino and the relic density of the higgsino-like neutralino receives contributions from the usual freeze-out mechanism along with contributions arising from the decay of hidden sector neutralinos. The model we propose is an extended MSSM model where the hidden sector is constituted of a $U(1{)}_X$ gauge sector along with matter charged under $U(1{)}_X$ which produce two neutralinos in the hidden sector. The $U(1{)}_X$ and the hypercharge $U(1{)}_Y$ of the MSSM have kinetic and Stueckelberg mass mixing where the mixings are ultraweak. In this case the hidden sector neutralinos have ultraweak interactions with the visible sector. Because of their ultraweak interactions the hidden sector neutralinos are not thermally produced and we assume their initial relic density to be negligible. However, they can be produced via interactions of MSSM particles in the early universe, and once produced they decay to the neutralino. For a range of mixings the decays occur before the BBN producing additional relic density for the neutralino. Models of this type are testable in dark matter direct and indirect detection experiments and at the high luminosity and high energy LHC.

    hep-phJHEP(2020)·9 citations
16. 16*

    How long does the hydrogen atom live?

    David McKeen🇨🇦 · Maxim Pospelov🇺🇸

    It is possible that the proton is stable while atomic hydrogen is not. This is the case in models with new particles carrying baryon number which are light enough to be stable themselves but heavy enough so that proton decay is kinematically blocked. Models of new physics that explain the neutron lifetime anomaly generically have this feature, allowing for atomic hydrogen to decay through electron capture on a proton. We calculate the radiative hydrogen decay rate involving the emission of a few hundred keV photon, which makes this process detectable in experiment. In particular, we show that the low energy part of the Borexino spectrum is sensitive to radiative hydrogen decay, and turn this into a limit on the hydrogen lifetime of order $10^{30}\mathrm{s}$ or stronger. For models where the neutron mixes with a dark baryon, $\chi$, this limits the mixing angle to roughly $10^{-11}$, restricting the $n\to \chi \gamma$ branching to $10^{-4}$, over a wide range of parameter space.

    hep-phhep-exnucl-exnucl-thUniverse(2023)·31 citations
17. 17*

    Updated constraints on the Georgi-Machacek model from LHC Run 2

    Ameen Ismail🇺🇸 · Heather E. Logan🇨🇦 · Yongcheng Wu🇨🇦

    We study the experimental constraints on the Georgi-Machacek model from direct searches for the new Higgs bosons and measurements of the properties of the discovered 125 GeV Higgs boson. We apply these by interfacing the public codes HiggsBounds 5.2.0 and HiggsSignals 2.2.1, which implement a large collection of direct-search constraints on extra Higgs bosons and measurements of the properties of the 125 GeV state to the model calculator GMCALC. We also implement constraints involving searches for doubly-charged Higgs bosons and Drell-Yan production of a neutral Higgs with decays to photon pairs directly into GMCALC; these channels are not included in HiggsBounds but provide important constraints on the model, especially at low mass. We identify new constraints on the model from $H_3^0\to Zh$ and $H\to hh$ and point out that these channels remain promising. We also determine the allowed range of couplings of the SM-like Higgs boson after all experimental constraints are applied and show that the direct searches for additional Higgs bosons are generally more constraining than the measurements of the 125 GeV Higgs boson couplings. The updated GMCALC code will be released as version 1.5.0.

    hep-phhep-ex38 citations
18. 18*

    Cosmological Bounds on sub-GeV Dark Vector Bosons from Electromagnetic Energy Injection

    John Coffey🇨🇦 · Lindsay Forestell🇨🇦 · David E. Morrissey🇨🇦 · Graham White🇨🇦

    New dark vector bosons that couple very feebly to regular matter can be created in the early universe and decay after the onset of big bang nucleosynthesis (BBN) or the formation of the cosmic microwave background (CMB) at recombination. The energy injected by such decays can alter the light element abundances or modify the power and frequency spectra of the CMB. In this work we study the constraints implied by these effects on a range of sub-GeV dark vectors including the kinetically mixed dark photon, and the $B-L$, $L_e-L_{\mu }$, $L_e-L_{\tau }$ , and $L_{\mu }-L_{\tau }$ dark U(1) bosons. We focus on the effects of electromagnetic energy injection, and we update previous investigations of dark photon and other dark vector decays by taking into account non-universality in the photon cascade spectrum relevant for BBN and the energy dependence of the ionization efficiency after recombination in our treatment of modifications to the CMB.

    hep-phastro-ph.COJHEP(2020)·26 citations
19. 19*

    Soft Fragmentation on the Celestial Sphere

    Duff Neill🇺🇸 · Felix Ringer🇺🇸

    We develop two approaches to the problem of soft fragmentation of hadrons in a gauge theory for high energy processes. The first approach directly adapts the standard resummation of the parton distribution function's anomalous dimension (that of twist-two local operators) in the forward scattering regime, using $k_T$-factorization and BFKL theory, to the case of the fragmentation function by exploiting the mapping between the dynamics of eikonal lines on transverse-plane to the celestial-sphere. Critically, to correctly resum the anomalous dimension of the fragmentation function under this mapping, one must pay careful attention to the role of regularization, despite the manifest collinear or infra-red finiteness of the BFKL equation. The anomalous dependence on energy in the celestial case, arising due to the mismatch of dimensionality between positions and angles, drives the differences between the space-like and time-like anomalous dimension of parton densities, even in a conformal theory. The second approach adapts an angular-ordered evolution equation, but working in 4-2$ϵ$ dimensions at all angles. The two approaches are united by demanding that the anomalous dimension in 4-2$ϵ$ dimensions for the parton distribution function determines the kernel for the angular-ordered evolution to all orders.

    hep-phhep-thnucl-thJHEP(2020)·27 citations
20. 20*

    Observable Gravitational Waves in Minimal Scotogenic Model

    Debasish Borah🇮🇳 · Arnab Dasgupta🇰🇷 · Kohei Fujikura🇯🇵 · Sin Kyu Kang🇰🇷 · Devabrat Mahanta🇮🇳

    We scrutinise the widely studied minimal scotogenic model of dark matter (DM) and radiative neutrino mass from the requirement of a strong first order electroweak phase transition (EWPT) and observable gravitational waves at future planned space based experiments. The scalar DM scenario is similar to inert scalar doublet extension of standard model where a strong first order EWPT favours a portion of the low mass regime of DM which is disfavoured by the latest direct detection bounds. In the fermion DM scenario, we get newer region of parameter space which favours strong first order EWPT as the restriction on mass ordering within inert scalar doublet gets relaxed. While such leptophilic fermion DM remains safe from stringent direct detection bounds, newly allowed low mass regime of charged scalar can leave tantalising signatures at colliders and can also induce charged lepton flavour violation within reach of future experiments. While we get such new region of parameter space satisfying DM relic, strong first order EWPT with detectable gravitational waves, light neutrino mass and other relevant constraints, we also improve upon previous analysis in similar model by incorporating appropriate resummation effects in effective finite temperature potential.

    hep-phastro-ph.COJCAP(2020)·27 citations
21. 21*

    Light $Z^{\prime }$ and Dark Matter from U(1)${}_X$ Gauge Symmetry

    Nobuchika Okada🇺🇸 · Satomi Okada🇺🇸 · Qaisar Shafi🇺🇸

    We consider a U(1)${}_X$ gauge symmetry extension of the Standard Model (SM) with a $Z^{\prime }$-portal Majorana fermion dark matter that allows for a relatively light gauge boson $Z^{\prime }$ with mass of 10 MeV$-$ a few GeV and a much heavier dark matter through the freeze-in mechanism. In a second scenario the roles are reversed, and the dark matter mass, in the keV range or so, lies well below the $Z^{\prime }$ mass, say, $\sim 1$ GeV. We outline the parameter space that can be explored for these two scenarios at the future Lifetime Frontier experiments including Belle-II, FASER, LDMX and SHiP.

    hep-phastro-ph.COhep-exPLB(2020)·42 citations
22. 22*

    An almost-entirely precise empirical estimation for various chemical potentials

    Hayam Yassin🇪🇬 · Eman R. Abo Elyazeed (Ain Shams U., Cairo)🇪🇬 · Abdel Nasser Tawfik (Nile U., ECTP)🇪🇬

    The transverse momentum spectra of the well-identified produced particles, ${\pi }^{+}$, ${\pi }^{-}$, $K^{+}$, $K^{-}$, $p$, $\bar{p}$, $K_s^0$, $\Lambda$, $\bar{\Lambda }$, ${\Xi }^{-}$, and ${\Xi }^{+}$ are analyzed in a statistical approach. From the partition function of grand-canonical ensemble, we propose a generic expression for the dependence of the generic chemical potential $\mu$ on the rapidity $y$. Then, by fitting this expression to the experimental results on the most central $p_{\perp }$ and $d^{2}N/2\pi p_{\perp }d{p}_{\perp }dy$, at energies ranging from $7.7$ to $200$GeV, we have introduced a generic expression for the rapidity dependence of $\mu$, at different energies, namely $\mu =a+b{y}^2$, where $a$ and $b$ is constants. We find that the resulting energy dependence $\sqrt{s_{\mathtt{NN}}}=c[(\mu -a)/b{]}^{d/2}$ agrees well with the statistical thermal models. We also present precise estimations of various types of chemical potentials, ${\mu }_B$, ${\mu }_S$, and ${\mu }_Q$, the baryon, the strangeness, and the charge chemical potential, respectively.

    hep-phResults Phys.(2022)·3 citations
23. 23*

    Looking through the QCD Conformal Window with Perturbation Theory

    Lorenzo Di Pietro🇮🇹 · Marco Serone🇮🇹

    We study the conformal window of QCD using perturbation theory, starting from the perturbative upper edge and going down as much as we can towards the strongly coupled regime. We do so by exploiting the available five-loop computation of the $\overline{\mathrm{MS}}$ $\beta$-function and employing Borel resummation techniques both for the ordinary perturbative series and for the Banks-Zaks conformal expansion. Large-$n_f$ results are also used. We argue that the perturbative series for the $\overline{\mathrm{MS}}$ $\beta$-function is most likely asymptotic and non-Borel resummable, yet Borel resummation techniques allow to improve on ordinary perturbation theory. We find substantial evidence that QCD with $n_f=12$ flavours flows in the IR to a conformal field theory. Though the evidence is weaker, we find indications that also $n_f=11$ might sit within the conformal window. We also compute the value of the mass anomalous dimension $\gamma$ at the fixed point and compare it with the available lattice results. The conformal window might extend for lower values of $n_f$, but our methods break down for $n_f<11$, where we expect that non-perturbative effects become important. A similar analysis is performed in the Veneziano limit.

    ↳ hep-thhep-lathep-phJHEP(2020)·30 citations
24. 24*

    Obtaining the sphaleron field configurations with gradient flow

    Yu Hamada🇯🇵 · Kengo Kikuchi🇯🇵

    We propose a formalism to obtain the electroweak sphaleron, which is one of the static classical solutions, using the gradient flow method. By adding a modification term to the gradient flow equation, we can obtain the sphaleron configuration as a stable fixed point of the flow in the large flow time. Applying the method to the $SU(2)$-Higgs model (the Weinberg angle ${\theta }_W$ is $0$) in four dimensions, we obtain the sphaleron configuration whose energy coincides with previous studies numerically. We can also show that the Chern-Simons number of the solution has a half-integer.

    ↳ hep-thhep-phPRD(2020)·14 citations
25. 25*

    An analytical approximation of the scalar spectrum in the ultra-slow-roll inflationary models

    Jing Liu🇨🇳 · Zong-Kuan Guo🇨🇳 · Rong-Gen Cai🇨🇳

    The ultra-slow-roll (USR) inflationary models predict large-amplitude scalar perturbations at small scales which can lead to the primordial black hole production and scalar-induced gravitational waves. In general scalar perturbations in the USR models can only be obtained using numerical method because the usual slow-roll approximation breaks. In this work, we propose an analytical approach to estimate the scalar spectrum which is consistent with the numerical result. We find that the USR inflationary models predict a peak with power-law slopes in the scalar spectrum and energy spectrum of gravitational waves, and we derive the expression of the spectral indexes in terms of the inflationary potential. In turn, the inflationary potential near the USR regime can be reconstructed from the negative spectral index of the gravitational wave energy spectrum.

    ↳ astro-ph.COgr-qchep-phPRD(2020)·93 citations
26. 26*

    Mean volume reflection angle

    M. V. Bondarenco🇺🇦

    The mean volume reflection angle of a high-energy charged particle passing through a bent crystal is expressed as an integral involving the effective interplanar potential over a single crystal period. Implications for positively and negatively charged particles, and silicon crystal orientations (110) and (111) are discussed. A generic next-to-leading-order expansion in the ratio $E/R$ of the particle energy $E$ to the crystal bending radius $R$ is given. For positively charged particles, the dependence of the mean volume reflection angle on $E/R$ proves to be approximately linear, whereas for negatively charged particles the linear behaviour is modified by an $E/R$-dependent logarithmic factor. Up-to-date experimental data are confronted with predictions based on commonly used atomic potentials.

    ↳ physics.acc-phhep-phPhys.Rev.Accel.Beams(2020)·1 citation
27. 27*

    The Power of Halometry

    Siddharth Mishra-Sharma🇺🇸 · Ken Van Tilburg🇺🇸 · Neal Weiner🇺🇸

    Astrometric weak gravitational lensing is a powerful probe of the distribution of matter on sub-Galactic scales, which harbor important information about the fundamental nature of dark matter. We propose a novel method that utilizes angular power spectra to search for the correlated pattern of apparent motions of celestial objects induced from time-dependent lensing by a population of Galactic subhalos. Application of this method to upcoming astrometric datasets will allow for the direct measurement of the properties of Galactic substructure, with implications for the underlying particle physics. We show that, with near-future astrometric observations, it may be possible to statistically detect populations of cold dark matter subhalos, compact objects, as well as density fluctuations sourced by scalar field dark matter. Currently-unconstrained parameter space will already be accessible using upcoming data from the ongoing Gaia mission.

    ↳ astro-ph.COastro-ph.HEastro-ph.IMhep-phPRD(2020)·28 citations
28. 28*

    Entanglement and quantum tomography with top quarks at the LHC

    Yoav Afik🇨🇭 · Juan Ramón Muñoz de Nova🇪🇸

    Entanglement is a central subject in quantum mechanics. Due to its genuine relativistic behavior and fundamental nature, high-energy colliders are attractive systems for the experimental study of fundamental aspects of quantum mechanics. We propose the detection of entanglement between the spins of top-antitop-quark pairs at the LHC, representing the first proposal of entanglement detection in a pair of quarks, and also the entanglement observation at the highest energy scale so far. We show that entanglement can be observed by direct measurement of the angular separation between the leptons arising from the decay of the top-antitop pair. The detection can be achieved with high statistical significance, using the current data recorded during Run 2 at the LHC. In addition, we develop a simple protocol for the quantum tomography of the top-antitop pair. This experimental technique reconstructs the quantum state of the system, providing a new experimental tool to test theoretical predictions. Our work explicitly implements canonical experimental techniques in quantum information in a two-qubit high-energy system, paving the way to use high-energy colliders to also study quantum information aspects.

    ↳ quant-phhep-exhep-phEur.Phys.J.Plus(2021)·258 citations
29. 29*

    Scaling solutions and weak gravity in dark energy with energy and momentum couplings

    Luca Amendola (Heidelberg University)🇩🇪 · Shinji Tsujikawa (Tokyo University of Science)🇯🇵

    We argue that the $\Lambda$CDM tensions of the Hubble-Lemaitre expansion rate $H_0$ and the clustering normalization ${\sigma }_8$ can be eased, at least in principle, by considering an interaction between dark energy and dark matter in such a way to induce a small and positive early effective equation of state and a weaker gravity. For a dark energy scalar field $\varphi$ interacting with dark matter through an exchange of both energy and momentum, we derive a general form of the Lagrangian allowing for the presence of scaling solutions. In a subclass of such interacting theories, we show the existence of a scaling $\varphi$-matter-dominated-era ($\varphi$MDE) which can potentially alleviate the $H_0$ tension by generating an effective high-redshift equation of state. We also study the evolution of perturbations for a model with $\varphi$MDE followed by cosmic acceleration and find that the effective gravitational coupling relevant to the linear growth of large-scale structures can be smaller than the Newton gravitational constant $G$ at low redshifts. The momentum exchange between dark energy and dark matter plays a crucial role for realizing weak gravity, while the energy transfer is also required for the existence of $\varphi$MDE.

    ↳ gr-qcastro-ph.COhep-phJCAP(2020)·55 citations
30. 30*

    Prospects and requirements of opaque detectors in accelerator neutrino experiments

    Jian Tang🇨🇳 · Sampsa Vihonen🇨🇳 · TseChun Wang🇨🇳

    Opaque detectors are a recently proposed novel detector concept where an opaque scintillator aligned with wavelength-shifting fibers is used to enable the discrimination of electron neutrinos and antineutrinos with a rather low energy threshold. In this work, we investigate the potential effects of the enhanced detection capabilities of the opaque detectors in accelerator neutrino experiments. Focusing on the energy threshold, energy resolution, detection efficiency and background suppression in the analysis of electron-like events, we determine whether using opaque detectors could lead to improvements in the CP violation and light sterile neutrino searches in the future accelerator neutrino experiments. We also identify the minimum requirements for the opaque detectors to reach the designated physics goals in the simulated experiments. We find that a 75.6% fraction of ${\delta }_{CP}$ values could be reached for CP violation discovery by 3$\sigma$ confidence level or better when opaque detectors of 120 kton and 130 kton fiducial masses are used together with neutrino beams from J-PARC and MOMENT, respectively, whereas near detectors placed about 250 m from sources are sufficient to exclude the gallium anomaly at 2$\sigma$ confidence level.

    ↳ physics.ins-dethep-exhep-phPRD(2020)·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.