Fri·Jan 29, 2016Friday·January 29, 2016

1. 01*

   Di-Photon excess in the 2HDM: hasting towards the instability and the non-perturbative regime

   Enrico Bertuzzo🇧🇷 · Pedro A.N. Machado🇪🇸 · Marco Taoso🇪🇸

   We challenge the interpretation of the di-photon excess recently observed by both ATLAS and CMS in a two Higgs doublet framework. Due to the large enhancement necessary to obtain the observed di-photon signal, a large number of colored and charged vector-like fermions are called for. We find that even before the hypercharge gauge coupling becomes non perturbative, the one loop effects of these fermions abruptly drive the scalar potential to instability.

   hep-phPRD(2016)·43 citations
2. 02*

   Neutrinoless double beta decay: 2015 review

   S. Dell'Oro🇮🇹 · S. Marcocci🇮🇹 · M. Viel🇮🇹 · F. Vissani🇮🇹

   The discovery of neutrino masses through the observation of oscillations boosted the importance of neutrinoless double beta decay ($0\nu \beta \beta$). In this paper, we review the main features of this process, underlining its key role both from the experimental and theoretical point of view. In particular, we contextualize the $0\nu \beta \beta$ in the panorama of lepton-number violating processes, also assessing some possible particle physics mechanisms mediating the process. Since the $0\nu \beta \beta$ existence is correlated with neutrino masses, we also review the state-of-art of the theoretical understanding of neutrino masses. In the final part, the status of current $0\nu \beta \beta$ experiments is presented and the prospects for the future hunt for $0\nu \beta \beta$ are discussed. Also, experimental data coming from cosmological surveys are considered and their impact on $0\nu \beta \beta$ expectations is examined.

   hep-phastro-ph.COAdv.High Energy Phys.(2016)·509 citations
3. 03*

   Unification of gauge, family, and flavor symmetries illustrated in gauged SU(12) models

   Carl H. Albright🇺🇸 · Robert P. Feger.🇩🇪 · Thomas W. Kephart🇺🇸

   To explain quark and lepton masses and mixing angles, one has to extend the standard model, and the usual practice is to put the quarks and leptons into irreducible representations of discrete groups. We argue that discrete flavor symmetries (and their concomitant problems) can be avoided if we extend the gauge group. In the framework of SU(12) we give explicit examples of models having varying degrees of predictability obtained by scanning over groups and representations and identifying cases with operators contributing to mass and mixing matrices that need little fine- tuning of prefactors. Fitting with quark and lepton masses run to the GUT scale and known mixing angles allows us to make predictions for the neutrino masses and hierarchy, the octant of the atmospheric mixing angle, leptonic CP violation, Majorana phases, and the effective mass observed in neutrinoless double beta decay.

   hep-phPRD(2016)·7 citations
4. 04*

   $Z_{BL}^{\prime }$ portal dark matter and LHC Run-2 results

   Nobuchika Okada🇺🇸 · Satomi Okada🇯🇵

   We consider a concise dark matter scenario in the minimal gauged $B-L$ extension of the Standard Model (SM), where the global $B-L$ (baryon number minus lepton number) symmetry in the SM is gauged, and three generations of right-handed neutrinos and a $B-L$ Higgs field are introduced. Associated with the $B-L$ gauge symmetry breaking by a VEV of the $B-L$ Higgs field, the seesaw mechanism for generating the neutrino mass is automatically implemented after the electroweak symmetry breaking in the SM. In this model context, we introduce a $Z_2$-parity and assign an odd parity for one right-handed neutrino while even parities for the other fields. Therefore, the dark matter candidate is identified as the right-handed Majorana neutrino with odd $Z_2$ parity, keeping the minimality of the particle content intact. When the dark matter particle communicates with the SM particles mainly through the $B-L$ gauge boson ($Z_{BL}^{\prime }$ boson), its relic abundance is determined by only three free parameters, the $B-L$ gauge coupling (${\alpha }_{BL}$), the $Z_{BL}^{\prime }$ boson mass ($m_{Z^{\prime }}$) and the dark matter mass ($m_{DM}$). With the cosmological upper bound on the dark matter relic abundance we find a lower bound on ${\alpha }_{BL}$ as a function of $m_{Z^{\prime }}$. On the other hand, we interpret the recent LHC Run-2 results on search for $Z^{\prime }$ boson resonance to an upper bound on ${\alpha }_{BL}$ as a function of $m_{Z^{\prime }}$. Combining the two results we identify an allowed parameter region for this "$Z_{BL}^{\prime }$ portal" dark matter scenario, which turns out to be a narrow window with the lower mass bound of $m_{Z^{\prime }}>2.5$ TeV.

   hep-phastro-ph.COhep-exPRD(2016)·113 citations
5. 05*

   Analysis of General Power Counting Rules in Effective Field Theory

   M.B. Gavela🇪🇸 · E.E. Jenkins🇺🇸 · A.V. Manohar🇺🇸 · L. Merlo🇪🇸

   We derive the general counting rules for a quantum effective field theory (EFT) in $\mathsf{d}$ dimensions. The rules are valid for strongly and weakly coupled theories, and predict that all kinetic energy terms are canonically normalized. They determine the energy dependence of scattering cross sections in the range of validity of the EFT expansion. We show that the size of cross sections is controlled by the $\Lambda$ power counting of EFT, not by chiral counting, even for chiral perturbation theory ($\chi$PT). The relation between $\Lambda$ and $f$ is generalized to $\mathsf{d}$ dimensions. We show that the naive dimensional analysis $4\pi$ counting is related to $\hslash$ counting. The EFT counting rules are applied to $\chi$PT, low-energy weak interactions, Standard Model EFT and the non-trivial case of Higgs EFT.

   hep-phEPJC(2016)·164 citations
6. 06*

   Gamma-rays from Dark Showers with Twin Higgs Models

   Marat Freytsis🇺🇸 · Simon Knapen🇺🇸 · Dean J. Robinson🇺🇸 · Yuhsin Tsai🇺🇸

   We consider a twin WIMP scenario whose twin sector contains a full dark copy of the SM hadrons, where the lightest twin particles are twin pions. By analogy to the standard WIMP paradigm, the dark matter (DM) freezes out through twin electroweak interactions, and annihilates into a dark shower of light twin hadrons. These are either stable or decay predominantly to standard model (SM) photons. We show that this 'hadrosymmetric' scenario can be consistent with all applicable astrophysical, cosmological and collider constraints. In order to decay the twin hadrons before the big-bang nucleosynthesis epoch, an additional portal between the SM and twin sector is required. In most cases we find this additional mediator is within reach of either the LHC or future intensity frontier experiments. Furthermore, we conduct simulations of the dark shower and consequent photon spectra. We find that fits of these spectra to the claimed galactic center gamma-ray excess seen by Fermi-LAT non-trivially coincide with regions of parameter space that both successfully generate the observed DM abundance and exhibit minimal fine-tuning.

   hep-phastro-ph.COJHEP(2016)·57 citations
7. 07*

   Hypercharge Axion and the Diphoton $750$ GeV Resonance

   Ido Ben-Dayan🇮🇱 · Ram Brustein🇮🇱

   The CMS and ATLAS reports on a possible excess of diphoton events at $750$ GeV are the cause of great excitement and hope. We show that a pseudoscalar axion coupled to the topological density of hypercharge, suggested in the past by Brustein and Oaknin as a candidate for inducing baryogenesis, can explain the signal in the diphoton channel. The hypercharge axion (HCA) can also decay to $Z\gamma$ and $ZZ$. The expected number of events in these channels is too small to have been detected, but such decays should be observed in the future. The HCA can be produced via vector boson fusion (VBF) or via associated production (AP). The latter should be manifested by a characteristic decay to 3 photons which should be observed soon. We adapt the previous analysis of possible detection of the HCA at the LHC by Brustein and Oaknin and by Elfgren to the case that the mass of the HCA is 750 GeV and find the expected cross section and decay width in terms of the HCA coupling. We find that the expected cross-section fits well the observed number of excess events and that there is tension between the measured cross-section and the reported partial decay width. The tension is caused because for both VBF and AP the production cross-section and the decay width depend linearly on each other. We therefore expect that if the new resonance is indeed the HCA, either its width should be significantly smaller than the reported width or the production cross-section should be significantly higher than the reported one.

   hep-phhep-ex38 citations
8. 08*

   Numerical Analysis of Coleman-de Luccia Tunneling

   Yuhei Goto🇯🇵 · Kazumi Okuyama🇯🇵

   We study the false vacuum decay of a single scalar field $\varphi$ coupled to gravity described by the Coleman-de Luccia (CdL) instanton. We show that it is possible to numerically calculate the bounce factor, which is related to the CdL tunneling rate, without using the thin-wall approximation. In this paper, we consider $1/\cosh (\varphi )$- and $\cos (\varphi )$-type potential as examples, which have cosmological and phenomenological applications. Especially, in the $\cos (\varphi )$-type potential we show that the range of values in which axion decay constant can take is restricted by the form of the periodic potential if the CdL tunneling occurs.

   hep-phInt.J.Mod.Phys.A(2016)·4 citations
9. 09*

   Probing the transversity spin structure of a nucleon in neutrino-production of a charmed meson

   B. Pire🇫🇷 · L. Szymanowski🇵🇱 · J. Wagner🇵🇱

   Including O(m_c) terms in the coefficient functions and/or O(m_D) twist 3 contributions in the heavy meson distribution amplitudes leads to a non-zero transverse amplitude for exclusive neutrino production of a D pseudoscalar charmed meson on an unpolarized target. We work in the framework of the collinear QCD approach where chiral-odd transversity generalized parton distributions (GPDs) factorize from perturbatively calculable coefficient functions.

   hep-phhep-exnucl-exnucl-thEPJ Web Conf.(2016)·8 citations
10. 10*

    Precise top mass determination using lepton distribution at LHC

    Sayaka Kawabata🇰🇷

    We present a new method to measure a theoretically well-defined mass of the top quark at the LHC. This method uses lepton energy distribution and has a boost-invariant nature. We perform a simulation analysis of the top mass reconstruction with this method for tt -> lepton+jets channel at the leading order. We estimate several major uncertainties in the top mass determination and find that they are under good control.

    hep-phPoS(2016)·0 citations
11. 11*

    Examination of directed flow as a signature of the softest point of the equation of state in QCD matter

    Yasushi Nara🇯🇵 · Harri Niemi🇩🇪 · Akira Ohnishi🇯🇵 · Horst Stoecker🇩🇪

    We analyze the directed flow of protons and pions in high-energy heavy-ion collisions in the incident energy range from $\sqrt{s_{NN}}=7.7$ to 27 GeV within a microscopic transport model. Standard hadronic transport approaches do not describe the collapse of directed flow below $\sqrt{s_{NN}}\simeq 20$ GeV. By contrast, a model which simulates effects of a softening of the equation of state, well describes the behavior of directed flow data recently obtained by the STAR Collaboration~\cite{STARv1}. We give a detailed analysis of how directed flow is generated. Particularly, we found that softening of effective equation of state at the overlapping region of two nuclei, i.e. the reaction stages where the system reaches high baryon density state, is needed to explain the observed collapse of proton directed flow within a hadronic transport approach.

    hep-phhep-exnucl-exnucl-thPRC(2016)·96 citations
12. 12*

    Constraining the non-standard interaction parameters in long baseline neutrino experiments

    Katri Huitu🇫🇮 · Timo J. Kärkkäinen🇫🇮 · Jukka Maalampi🇫🇮 · Sampsa Vihonen🇫🇮

    In this article we investigate the prospects for probing the strength of the possible non-standard neutrino interactions (NSI) in long baseline neutrino oscillation experiments. We find that these experiments are sensitive to NSI couplings down to the level of 0.01-0.1 depending on the oscillation channel and the baseline length, as well as on the detector's fiducial mass. We also investigate the interference of the leptonic CP angle ${\delta }_{CP}$ with the constraining of the NSI couplings. It is found that the interference is strong in the case of the ${\nu }_e\leftrightarrow {\nu }_{\mu }$ and ${\nu }_e\leftrightarrow {\nu }_{\tau }$ transitions but not significant in other transitions. In our numerical analysis we apply the GLoBES software and use the LBNO setup as our benchmark.

    hep-phPRD(2016)·56 citations
13. 13*

    New pole contribution to $P_{h\perp }$-weighted single-transverse spin asymmetry in semi-inclusive deep inelastic scattering

    Shinsuke Yoshida (CCNU)🇨🇳

    In this paper, we discuss the new hard pole contribution to the $P_{h\perp }$-weighted single-transverse spin asymmetry in semi-inclusive deep inelastic scattering. We perform the complete next-to-leading order calculation of the $P_{h\perp }$-weighted cross section and show that the new hard pole contribution is required in order to obtain the complete evolution equation for the Qiu-Sterman function derived by different approaches.

    hep-phPRD(2016)·22 citations
14. 14*

    Baryogenesis via Elementary Goldstone Higgs Relaxation

    Helene Gertov🇩🇰 · Lauren Pearce🇺🇸 · Francesco Sannino🇩🇰 · Louis Yang🇺🇸

    We extend the relaxation mechanism to the Elementary Goldstone Higgs framework. Besides studying the allowed parameter space of the theory we add the minimal ingredients needed for the framework to be phenomenologically viable. The very nature of the extended Higgs sector allows to consider very flat scalar potential directions along which the relaxation mechanism can be implemented. This fact translates into wider regions of applicability of the relaxation mechanism when compared to the Standard Model Higgs case. Our results show that, if the electroweak scale is not fundamental but radiatively generated, it is possible to generate the observed matter-antimatter asymmetry via the relaxation mechanism.

    hep-phastro-ph.COPRD(2016)·9 citations
15. 15*

    SUSY effects in $R_b$: revisited under current experimental constraints

    Wei Su🇨🇳 · Jin Min Yang🇨🇳

    In this note we revisit the SUSY effects in $R_b$ under current experimental constraints including the LHC Higgs data, the $B$-physics measurements, the dark matter relic density and direct detection limits, as well as the precision electroweak data. We first perform a scan to figure out the currently allowed parameter space and then display the SUSY effects in $R_b$. We find that although the SUSY parameter space has been severely restrained by current experimental data, both the general MSSM and the natural-SUSY scenario can still alter $R_b$ with a magnitude sizable enough to be observed at future $Z$-factories (ILC, CEPC, FCC-ee, Super $Z$-factory) which produce $10^9-10^{12}$ $Z$-bosons. To be specific, assuming a precise measurement $\delta R_b=2.0\times 10^{-5}$ at FCC-ee, we can probe a right-handed stop up to 530 GeV through chargino-stop loops, probe a sbottom to 850 GeV through neutralino-sbottom loops and a charged Higgs to 770 GeV through the Higgs-top quark loops for a large $\text{tan}\beta$. The full one-loop SUSY correction to $R_b$ can reach $1\times 10^{-4}$ in natural SUSY and $2\times 10^{-4}$ in the general MSSM.

    hep-phPLB(2016)·7 citations
16. 16*

    Advantages of exclusive \gamma\gamma production to probe high mass systems

    A.D. Martin🇬🇧 · M.G. Ryskin🇬🇧

    We recall that the exclusive production of high mass objects via \gamma\gamma fusion at the LHC is not strongly suppressed in comparison with inclusive \gamma\gamma fusion. Therefore it may be promising to study new objects produced by the \gamma\gamma subprocess in experiments with exclusive kinematics. We list the main advantages of exclusive experiments. We discuss the special advantage of observing $\gamma \gamma \to X\to \gamma Z$ exclusive events.

    hep-phJ.Phys.G(2016)·21 citations
17. 17*

    Neutrino masses and mixings: Status of known and unknown $3\nu$ parameters

    F.Capozzi🇮🇹 · E. Lisi🇮🇹 · A. Marrone🇮🇹 · D. Montanino🇮🇹 · A. Palazzo🇮🇹

    Within the standard 3nu mass-mixing framework, we present an up-to-date global analysis of neutrino oscillation data (as of January 2016), including the latest available results from experiments with atmospheric neutrinos (Super-Kamiokande and IceCube DeepCore), at accelerators (first T2K anti-nu and NOvA nu runs in both appearance and disappearance mode), and at short-baseline reactors (Daya Bay and RENO far/near spectral ratios), as well as a reanalysis of older KamLAND data in the light of the "bump" feature recently observed in reactor spectra. We discuss improved constraints on the five known oscillation parameters (delta m^2, |Delta m^2|, sin^2theta_12, sin^2theta_13, sin^2theta_23), and the status of the three remaining unknown parameters: the mass hierarchy, the theta_23 octant, and the possible CP-violating phase delta. With respect to previous global fits, we find that the reanalysis of KamLAND data induces a slight decrease of both delta m^2 and sin^2theta_12, while the latest accelerator and atmospheric data induce a slight increase of |Delta m^2|. Concerning the unknown parameters, we confirm the previous intriguing preference for negative values of sin(delta) [with best-fit values around sin(delta) ~ -0.9], but we find no statistically significant indication about the theta_23 octant or the mass hierarchy (normal or inverted). Assuming an alternative (so-called LEM) analysis of NOvA data, some delta ranges can be excluded at >3 sigma, and the normal mass hierarchy appears to be slightly favored at 90% C.L. We also describe in detail the covariances of selected pairs of oscillation parameters. Finally, we briefly discuss the implications of the above results on the three non-oscillation observables sensitive to the (unknown) absolute nu mass scale: the sum of nu masses, the effective nu_e mass, and the effective Majorana mass.

    hep-phNPB(2016)·340 citations
18. 18*

    Iterative Monte Carlo analysis of spin-dependent parton distributions

    Nobuo Sato🇺🇸 · W. Melnitchouk🇺🇸 · S. E. Kuhn🇺🇸 · J. J. Ethier🇺🇸 · A. Accardi🇺🇸

    We present a comprehensive new global QCD analysis of polarized inclusive deep-inelastic scattering, including the latest high-precision data on longitudinal and transverse polarization asymmetries from Jefferson Lab and elsewhere. The analysis is performed using a new iterative Monte Carlo fitting technique which generates stable fits to polarized parton distribution functions (PDFs) with statistically rigorous uncertainties. Inclusion of the Jefferson Lab data leads to a reduction in the PDF errors for the valence and sea quarks, as well as in the gluon polarization uncertainty at $x\gtrsim 0.1$. The study also provides the first determination of the flavor-separated twist-3 PDFs and the $d_2$ moment of the nucleon within a global PDF analysis.

    hep-phhep-exnucl-thPRD(2016)·191 citations
19. 19*

    Electroweak corrections to $pp\to {\mu }^{+}{\mu }^{-}{e}^{+}{e}^{-}+X$ at the LHC -- a Higgs background study

    B.Biedermann🇩🇪 · A.Denner🇩🇪 · S.Dittmaier🇩🇪 · L.Hofer🇪🇸 · B.Jäger🇩🇪

    The first complete calculation of the next-to-leading-order electroweak corrections to four-lepton production at the LHC is presented, where all off-shell effects of intermediate Z bosons and photons are taken into account. Focusing on the mixed final state ${\mu }^{+}{\mu }^{-}{e}^{+}{e}^{-}$, we study differential cross sections that are particularly interesting for Higgs-boson analyses. The electroweak corrections are divided into photonic and purely weak corrections. The former exhibit patterns familiar from similar W/Z-boson production processes with very large radiative tails near resonances and kinematical shoulders. The weak corrections are of the generic size of 5% and show interesting variations, in particular a sign change between the regions of resonant Z-pair production and the Higgs signal.

    hep-phPRL(2016)·123 citations
20. 20*

    Asymptocic Freedom of Gluons in Hamiltonian Dynamics

    María Gómez-Rocha🇮🇹 · Stanisław D. Głazek🇵🇱

    We derive asymptotic freedom of gluons in terms of the renormalized $SU(3)$ Yang-Mills Hamiltonian in the Fock space. Namely, we use the renormalization group procedure for effective particles (RGPEP) to calculate the three-gluon interaction term in the front-form Yang-Mills Hamiltonian using a perturbative expansion in powers of $g$ up to third order. The resulting three-gluon vertex is a function of the scale parameter $s$ that has an interpretation of the size of effective gluons. The corresponding Hamiltonian running coupling constant exhibits asymptotic freedom, and the corresponding Hamiltonian $\beta$-function coincides with the one obtained in an earlier calculation using a different generator.

    hep-phFew Body Syst.(2016)·0 citations
21. 21*

    Possible interpretation on the origin of four-fermion interaction

    Hiroaki Kohyama🇹🇼

    We present a possible interpretation on the origin of the four-fermion interaction used in effective field theories. Inspired by the sharp momentum peak seen in Bose-Einstein condensate state, we incorporate the special gluon condensate effect into the gluon propagator. We then find that, if one considers hypothetic situation with the condensed gluon, the four-fermion contact interaction can arise from the first principle theory of quantum chromodynamics.

    hep-ph4 citations
22. 22*

    Another look at synchronized neutrino oscillations

    Evgeny Akhmedov🇩🇪 · Alessandro Mirizzi🇮🇹

    In dense neutrino backgrounds present in supernovae and in the early Universe neutrino oscillations may exhibit complex collective phenomena, such as synchronized oscillations, bipolar oscillations and spectral splits and swaps. We consider in detail possible decoherence effects on the simplest of these phenomena -- synchronized neutrino oscillations that can occur in a uniform and isotropic neutrino gas. We develop an exact formalism of spectral moments of the flavour spin vectors describing such a system and then apply it to find analytical approaches that allow one to study decoherence effects on its late-time evolution. This turns out to be possible in part due to the existence of the (previously unknown) exact conservation law satisfied by the quantities describing the considered neutrino system. Interpretation of the decoherence effects in terms of neutrino wave packet separation is also given, both in the adiabatic and non-adiabatic regimes of neutrino flavour evolution.

    hep-phastro-ph.HENPB(2016)·19 citations
23. 23*

    Mueller-Navelet jets at 13 TeV LHC: dependence on dynamic constraints in the central rapidity region

    Francesco Giovanni Celiberto🇮🇹 · Dmitry Yu. Ivanov🇷🇺 · Beatrice Murdaca🇮🇹 · Alessandro Papa🇮🇹

    We study the production of Mueller-Navelet jets at 13 TeV LHC, within collinear factorization and including the BFKL resummation of energy logarithms in the next-to-leading approximation. We calculate several azimuthal correlations for different values of the rapidity separation $Y$ between the two jets and evaluate the effect of excluding those events where, for a given $Y$, one of the two jets is produced in the central region.

    hep-phEPJC(2016)·103 citations
24. 24*

    String/M-theories About Our World Are Testable in the traditional Physics Way

    Gordon L. Kane🇺🇸

    Some physicists hope to use string/M-theory to construct a comprehensive underlying theory of our physical world a "final theory". Can such a theory be tested? A quantum theory of gravity must be formulated in 10 dimensions, so obviously testing it experimentally requires projecting it onto our 4D world (called "compactification"). Most string theorists study theories, including aspects such as AdS/CFT, not phenomena, and are not much interested in testing theories beyond the Standard Model about our world. Compactified theories generically have many realistic features whose necessary presence provides some tests, such as gravity, Yang-Mills forces like the Standard Model ones, chiral fermions that lead to parity violation, softly broken supersymmetry, Higgs physics, families, hierarchical fermion masses and more. All tests of theories in physics have always depended on assumptions and approximate calculations, and tests of compactified string/M-theories do too. String phenomenologists have also formulated some explicit tests for compactified theories. In particular, I give examples of tests from compactified M-theory (involving Higgs physics, predictions for superpartners at LHC, electric dipole moments, and more). It is clear that compactified theories exist that can describe worlds like ours, and it is clear that even if a multiverse were real it does not prevent us from finding comprehensive compactified theories like one that might describe our world. I also discuss what we might mean by a final theory, what we might want it to explain, and comment briefly on multiverse issues from the point of view of finding a theory that describes our world.

    ↳ hep-thhep-ph2 citations
25. 25*

    Collapsing shells, critical phenomena and black hole formation

    Vitor Cardoso🇵🇹 · Jorge V. Rocha🇪🇸

    We study the gravitational collapse of two thin shells of matter, in asymptotically flat spacetime or constrained to move within a spherical box. We show that this simple two-body system has surprisingly rich dynamics, which includes prompt collapse to a black hole, perpetually oscillating solutions or black hole formation at arbitrarily large times. Collapse is induced by shell crossing and the black hole mass depends sensitively on the number of shell crossings. At certain critical points, the black hole mass exhibits critical behavior, determined by the change in parity (even or odd) of the number of crossings, with or without mass-gap during the transition. Some of the features we observe are reminiscent of confined scalars undergoing "turbulent" dynamics.

    ↳ gr-qchep-phhep-thPRD(2016)·20 citations
26. 26*

    Astrophysical constraints on resonantly produced sterile neutrino dark matter

    Aurel Schneider🇨🇭

    Resonantly produced sterile neutrinos are considered an attractive dark matter (DM) candidate only requiring a minimal, well motivated extension to the standard model of particle physics. With a particle mass restricted to the keV range, sterile neutrinos are furthermore a prime candidate for warm DM, characterised by suppressed matter perturbations at the smallest observable scales. In this paper we take a critical look at the validity of the resonant scenario in the context of constraints from structure formation. We compare predicted and observed number of Milky-Way satellites and we introduce a new method to generalise existing Lyman-$\alpha$ limits based on thermal relic warm DM to the case of resonant sterile neutrino DM. The tightest limits come from the Lyman-$\alpha$ analysis, excluding the entire parameter space (at 2-$\sigma$ confidence level) still allowed by X-ray observations. Constraints from Milky-Way satellite counts are less stringent, leaving room for resonant sterile neutrino DM most notably around the suggested line signal at 7.1 keV.

    ↳ astro-ph.COhep-phJCAP(2016)·141 citations
27. 27*

    Dark Radiation and Inflationary Freedom after Planck 2015

    Eleonora Di Valentino🇫🇷 · Stefano Gariazzo🇮🇹 · Martina Gerbino🇸🇪 · Elena Giusarma🇺🇸 · Olga Mena🇪🇸

    The simplest inflationary models predict a primordial power spectrum (PPS) of the curvature fluctuations that can be described by a power-law function that is nearly scale-invariant. It has been shown, however, that the low-multipole spectrum of the CMB anisotropies may hint the presence of some features in the shape of the scalar PPS, which could deviate from its canonical power-law form. We study the possible degeneracies of this non-standard PPS with the neutrino anisotropies, the neutrino masses, the effective number of relativistic species and a sterile neutrino or a thermal axion mass. The limits on these additional parameters are less constraining in a model with a non-standard PPS when only including the temperature auto-correlation spectrum measurements in the data analyses. The inclusion of the polarization spectra noticeably helps in reducing the degeneracies, leading to results that typically show no deviation from the $\Lambda$CDM model with a standard power-law PPS.

    ↳ astro-ph.COhep-phPRD(2016)·45 citations
28. 28*

    Revisiting light stringy states in view of the 750 GeV diphoton excess

    Pascal Anastasopoulos🇦🇹 · Massimo Bianchi🇮🇹

    We investigate light massive string states that appear at brane intersections. They replicate the massless spectrum in a richer fashion and may be parametrically lighter than standard Regge excitations. We identify the first few physical states and determine their BRST invariant vertex operators. In the supersymmetric case we reconstruct the super-multiplet structure. We then compute some simple interactions, such as the decay rate of a massive scalar or vector into two massless fermions. Finally we suggest an alternative interpretation of the 750 GeV diphoton excess at LHC in terms of a light massive string state, a replica of the Standard Model Higgs.

    ↳ hep-thhep-phNPB(2016)·14 citations
29. 29*

    Vacuum polarization of planar Dirac fermions by a superstrong Coulomb potential

    V.R. Khalilov🇷🇺 · I.V. Mamsurov🇷🇺

    We study the vacuum polarization of planar charged Dirac fermions by a strong Coulomb potential. Induced vacuum charge density is calculated and analyzed at the subcritical and supercritical Coulomb potentials for massless and massive fermions. For the massless case the induced vacuum charge density is localized at the origin when the Coulomb center charge is subcritical while it has a power-law tail when the Coulomb center charge is supercritical. The finite mass contribution into the induced charge due to the vacuum polarization is small and insignificantly distorts the Coulomb potential only at distances of order of the Compton length. The induced vacuum charge has a screening sign. As is known the quantum electrodynamics vacuum becomes unstable when the Coulomb center charge is increased from subcritical to supercritical values. In the supercritical Coulomb potential the quantum electrodynamics vacuum acquires the charge due to the so-called real vacuum polarization. We calculate the real vacuum polarization charge density. Screening of the Coulomb center charge are briefly discussed. We expect that our results will be helpful for more deep understanding of the fundamental problem of quantum electrodynamics and can as a matter of principle be tested in graphene with a supercritical Coulomb impurity.

    ↳ quant-phhep-ph0 citations
30. 30*

    Isocurvature Constraints on Portal Couplings

    Kimmo Kainulainen🇫🇮 · Sami Nurmi🇫🇮 · Tommi Tenkanen🇫🇮 · Kimmo Tuominen🇫🇮 · Ville Vaskonen🇫🇮

    We consider portal models which are ultraweakly coupled with the Standard Model, and confront them with observational constraints on dark matter abundance and isocurvature perturbations. We assume the hidden sector to contain a real singlet scalar $s$ and a sterile neutrino $\psi$ coupled to $s$ via a pseudoscalar Yukawa term. During inflation, a primordial condensate consisting of the singlet scalar $s$ is generated, and its contribution to the isocurvature perturbations is imprinted onto the dark matter abundance. We compute the total dark matter abundance including the contributions from condensate decay and nonthermal production from the Standard Model sector. We then use the Planck limit on isocurvature perturbations to derive a novel constraint connecting dark matter mass and the singlet self coupling with the scale of inflation: $m_{\mathrm{DM}}/\mathrm{GeV}\lesssim 0.2{\lambda }_{\mathrm{s}}^{3/8}{\left(H_{\ast }/10^{11}\mathrm{GeV}\right)}^{-3/2}$. This constraint is relevant in most portal models ultraweakly coupled with the Standard Model and containing light singlet scalar fields.

    ↳ astro-ph.COhep-phJCAP(2016)·91 citations
31. 31*

    Preheating and Entropy Perturbations in Axion Monodromy Inflation

    Evan McDonough🇨🇦 · Hossein Bazrafshan Moghaddam🇨🇦 · Robert H. Brandenberger🇨🇦

    We study the preheating of gauge fields in a simple axion monodromy model and compute the induced entropy perturbations and their effect on the curvature fluctuations. We find that the correction to the spectrum of curvature perturbations has a blue spectrum with index $n_s=5/2$. Hence, these induced modes are harmless for the observed structure of the universe. Since the spectrum is blue, there is the danger of overproduction of primordial black holes. However, we show that the observational constraints are easily satisfied.

    ↳ hep-thastro-ph.COgr-qchep-phJCAP(2016)·41 citations
32. 32*

    Probabilities and signalling in quantum field theory

    Robert Dickinson🇬🇧 · Jeff Forshaw🇬🇧 · Peter Millington🇬🇧

    We present an approach to computing probabilities in quantum field theory for a wide class of source-detector models. The approach works directly with probabilities and not with squared matrix elements, and the resulting probabilities can be written in terms of expectation values of nested commutators and anti-commutators. We present results that help in the evaluation of these, including an expression for the vacuum expectation values of general nestings of commutators and anti-commutators in scalar field theory. This approach allows one to see clearly how faster-than-light signalling is prevented, because it leads to a diagrammatic expansion in which the retarded propagator plays a prominent role. We illustrate the formalism using the simple case of the much-studied Fermi two-atom problem.

    ↳ hep-thhep-phmath-phmath.MP+1PRD(2016)·24 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.