HEP Phenomenology·hep-ph
21 papers—11 primary·10 cross-listed·reconstructed*
We discuss the cosmological constant puzzle and possible connections to the (meta-)stability of the Higgs vacuum suggested by recent LHC results. A possible explanation involves new critical phenomena in the ultraviolet, close to the Planck scale.
Hsin-Chia Cheng🇺🇸 · Sunghoon Jung🇰🇷 · Ennio Salvioni🇺🇸 · Yuhsin Tsai🇺🇸
The Twin Higgs model provides a natural theory for the electroweak symmetry breaking without the need of new particles carrying the standard model gauge charges below a few TeV. In the low energy theory, the only probe comes from the mixing of the Higgs fields in the standard model and twin sectors. However, an ultraviolet completion is required below ~ 10 TeV to remove residual logarithmic divergences. In non-supersymmetric completions, new exotic fermions charged under both the standard model and twin gauge symmetries have to be present to accompany the top quark, thus providing a high energy probe of the model. Some of them carry standard model color, and may therefore be copiously produced at current or future hadron colliders. Once produced, these exotic quarks can decay into a top together with twin sector particles. If the twin sector particles escape the detection, we have the irreducible stop-like signals. On the other hand, some twin sector particles may decay back into the standard model particles with long lifetimes, giving spectacular displaced vertex signals in combination with the prompt top quarks. This happens in the Fraternal Twin Higgs scenario with typical parameters, and sometimes is even necessary for cosmological reasons. We study the potential displaced vertex signals from the decays of the twin bottomonia, twin glueballs, and twin leptons in the Fraternal Twin Higgs scenario. Depending on the details of the twin sector, the exotic quarks may be probed up to ~ 2.5 TeV at the LHC and beyond 10 TeV at a future 100 TeV collider, providing a strong test of this class of ultraviolet completions.
Rikkert Frederix🇩🇪 · Keith Hamilton🇬🇧
We consider improving POWHEG+MINLO simulations, so as to also render them NLO accurate in the description of observables receiving contributions from events with lower parton multiplicity than present in their underlying NLO calculation. On a conceptual level we follow the strategy of the so-called MINLO' programs. Whereas the existing MINLO' framework requires explicit analytic input from higher order resummation, here we derive an effective numerical approximation to these ingredients, by imposing unitarity. This offers a way of extending the MINLO' method to more complex processes, complementary to the known route which uses explicit computations of high-accuracy resummation inputs. Specifically, we have focused on Higgs-plus-two-jet production (HJJ) and related processes. We also consider how one can cover three units of multiplicity at NLO accuracy, i.e. we consider how the HJJ-MINLO simulation may yield NLO accuracy for inclusive H, HJ, and HJJ quantities. We perform a feasibility study assessing the potential of these ideas.
M. Baker🇺🇸
Effective magnetic gauge theory with classical flux tubes of intrinsic width is an effective field theory of the long distance quark-antiquark interaction in Yang-Mills theory. Long wavelength fluctuations of the vortices of this theory lead to an effective string theory. In this paper we clarify the connection between effective field theory and effective string theory and we propose a new constraint on these vortices. We first examine the impact of string fluctuations on the classical dual superconductor description of confinement. At inter-quark distances the classical action for a straight flux tube determines the heavy quark potentials. At distances fluctuations of the flux tube axis give rise to an effective string theory with an action , the classical action for a curved flux tube, evaluated in the limit . This action is equal to the Nambu-Goto action. These conclusions are independent of the details of the flux tube. Further, we assume the QCD flux tube satisfies the additional constraint: where is the value of the component of the stress tensor at a distance from the axis of an infinite flux tube. Under this constraint the string tension equals the force on a quark in the chromoelectric field of an infinite straight flux tube, and the Nambu-Goto action can be represented in terms of the chromodynamic fields of effective magnetic gauge theory, yielding a field theory interpretation of effective string theory.
A sterile neutrino is a well-motivated and widely studied dark matter candidate. The most straightforward realization of sterile neutrino dark matter, through the Dodelson-Widrow mechanism, is now ruled out by a combination of X-ray and Lyman-\alpha measurements. An alternative production mechanism that is becoming increasingly popular in the literature is the freeze-in mechanism, involving frameworks where a feeble coupling to a particle - usually a scalar beyond the Standard Model - in the thermal bath results in a gradual accumulation of the sterile neutrino dark matter abundance. This article reviews the various motivations for realizing such frameworks in the literature, their common characteristic features, and phenomenological signatures.
Camilo Garcia-Cely🇧🇪 · Michael Gustafsson🇩🇪 · Alejandro Ibarra🇩🇪
We present a detailed study of the annihilation signals of the inert dark matter doublet model in its high mass regime. Concretely, we study the prospects to observe gamma-ray signals of the model in current and projected Cherenkov telescopes taking into account the Sommerfeld effect and including the contribution to the spectrum from gamma-ray lines as well as from internal bremsstrahlung. We show that present observations of the galactic center by the H.E.S.S. instrument are able to exclude regions of the parameter space that give the correct dark matter relic abundance. In particular, models with the charged and the neutral components of the inert doublet nearly degenerate in mass have strong gamma-ray signals. Furthermore, for dark matter particle masses above 1 TeV, we find that the non-observation of the continuum of photons generated by the hadronization of the annihilation products typically gives stronger constraints on the model parameters than the sharp spectral features associated to annihilation into monochromatic photons and the internal bremsstrahlung process. Lastly, we also analyze the interplay between indirect and direct detection searches for this model, concluding that the prospects for the former are more promising. In particular, we find that the upcoming Cherenkov Telescope Array will be able to probe a significant part of the high mass regime of the model.
E. N. Polanco-Euán🇲🇽 · V. Gupta🇲🇽 · G. Sánchez-Colón🇲🇽 · B.A. Bambah🇮🇳
The decays of the antisymmetric dibaryon octet into two baryon octets are considered. Sum rules for these decays in first order broken SU(3) are given. An SU(4) extension of the analysis is commented upon. Possibilities for the experimental observation of multibaryon and anti-multibaryon states is pointed out.
Jason Aebischer🇨🇭 · Andreas Crivellin🇨🇭 · Matteo Fael🇨🇭 · Christoph Greub🇨🇭
New physics realized above the electroweak scale can be encoded in a model independent way in the Wilson coefficients of higher dimensional operators which are invariant under the Standard Model gauge group. In this article, we study the matching of the gauge invariant dim-6 operators on the standard physics Hamiltonian relevant for and transitions. The matching is performed at the electroweak scale (after spontaneous symmetry breaking) by integrating out the top quark, , and the Higgs particle. We first carry out the matching of the dim-6 operators that give a contribution at tree level to the low energy Hamiltonian. In a second step, we identify those gauge invariant operators that do not enter transitions already at tree level, but can give relevant one-loop matching effects.
Andrzej J. Buras🇩🇪 · Fulvia De Fazio🇮🇹
Motivated by the recent findings that the ratio in the Standard Model (SM) appears to be significantly below the data we investigate whether the necessary enhancement of this ratio can be obtained in 331 models, in which new physics (NP) contributions to and other flavour observables are dominated by tree-level exchanges of a . NP contributions to in these models are governed by the electroweak operator for which the hadronic matrix element is rather well known so that our analysis of NP contributions is subject to much smaller uncertainties than within the SM. We consider seven 331 models selected in our earlier analysis on the basis of electroweak precision data. Imposing the constraints from transitions we find that only three of these models can provide a significant positive shift in up to for TeV. Two of them allow simultaneously a supression of by , bringing the theory closer to the data without any significant impact on the Wilson coefficient . The third one provides also the shift , softening the anomalies in , without any significant impact on . NP effects in rare decays and in turn out to be small. The flavour structure of 331 models implies that even for Tev a shift of up to and a significant shift in can be obtained, while the effects in other flavour observables are small.
Yi-Lei Tang🇨🇳 · Shou-hua Zhu🇨🇳
In this paper, we will discuss a specific case that the dark matter particles annihilate into right-handed neutrinos. We calculate the predicted gamma-ray excess from the galactic center and compare our results with the data from the Fermi-LAT. An approximately 10-60 GeV right-handed neutrino with heavier dark matter particle can perfectly explain the observed spectrum. The annihilation cross section falls within the range -, which is roughly compatible with the WIMP annihilation cross section.
Ahmad Sadeghi🇮🇷 · Mahdi Torabian🇮🇷
In this note we present a framework in which the weak scale appears dynamically technically natural with no new physics up to the Planck scale. The mixing between the massless Higgs and the R^2 metric theory induces, in canonical parametrization of the Einstein frame, an effective field-dependent Higgs mass parameter. It is a dynamical variable which in the course of cosmic evolution scans a wide range of values and eventually stabilizes at a low scale. The one-loop effective potential has an electroweak symmetry breaking vacuum and the hierarchy is explained by dimensional transmutation and cosmological relaxation mechanisms. Furthermore, by evaluating the renormalization group improved effective potential we find that the electroweak vacuum is the global minimum of the effective potential.
John Ellis🇬🇧 · Nick E. Mavromatos🇬🇧 · Dimitri P. Skliros🇬🇧
We introduce a new prescription for quantising scalar field theories perturbatively around a true minimum of the full quantum effective action, which is to `complete normal order' the bare action of interest. When the true vacuum of the theory is located at zero field value, the key property of this prescription is the automatic cancellation, to any finite order in perturbation theory, of all tadpole and, more generally, all `cephalopod' Feynman diagrams. The latter are connected diagrams that can be disconnected into two pieces by cutting one internal vertex, with either one or both pieces free from external lines. In addition, this procedure of `complete normal ordering' (which is an extension of the standard field theory definition of normal ordering) reduces by a substantial factor the number of Feynman diagrams to be calculated at any given loop order. We illustrate explicitly the complete normal ordering procedure and the cancellation of cephalopod diagrams in scalar field theories with non-derivative interactions, and by using a point splitting `trick' we extend this result to theories with derivative interactions, such as those appearing as non-linear sigma-models in the world-sheet formulation of string theory. We focus here on theories with trivial vacua, generalising the discussion to non-trivial vacua in a follow-up paper.
Gianluca Calcagni🇪🇸 · Giuseppe Nardelli🇮🇹 · David Rodríguez-Fernández🇪🇸
We study electroweak interactions in the multiscale theory with -derivatives, a framework where spacetime has the typical features of a multifractal. In the simplest case with only one characteristic time, length and energy scale , , and , we consider (i) the muon decay rate and (ii) the Lamb shift in the hydrogen atom, and constrain the corrections to the ordinary results. We obtain the independent absolute upper bounds (i) and (ii) . Under some mild theoretical assumptions, the Lamb shift alone yields the even tighter ranges , , and . To date, these are the first robust constraints on the scales at which the multifractal features of the geometry can become important in a physical process.
Kenta Miyahara🇯🇵 · Tetsuo Hyodo🇯🇵
We discuss the spacial structure of the resonance state, Lambda(1405), solving the Schrodinger equation with the KbarN local potential. The potential is constructed by paying attention to the two points, the constraint from the recent experimental data and the reliability in the complex energy region. Using the new local potential, we investigate the KbarN spacial structure and obtain the result indicating that Lambda(1405) is the meson-baryon molecular state, that is, the composite state.
Jia-Jun Wu🇦🇺 · B. S. Zou🇨🇳
The classical quenched quark models with three constituent quarks provide a good description for the baryon spatial ground states, but fail to reproduce the spectrum of baryon excited states. More and more evidences suggest that unquenched effects with multi-quark dynamics are necessary ingredients to solve the problem. Several new hyperon resonances reported recently could fit in the picture of penta-quark states. Based on this picture, some new hyperon excited states were predicted to exist; meanwhile with extension from strangeness to charm and beauty, super-heavy narrow and resonances with hidden charm or beauty were predicted to be around 4.3 and 11 GeV, respectively. Recently, two of such with hidden charm might have been observed by the LHCb experiment. More of those states are expected to be observed in near future. This opens a new window in order to study hadronic dynamics for the multi-quark states.
Zisheng Wang🇨🇳 · Hui Pan🇨🇳
We propose a new approach to explore CPT violation of neutrino oscillation through a fluctuating matter based on time-dependent geometric quantities. By mapping the neutrino oscillation onto a Poincare sphere structure, we obtain an analytic solution of master equation and further define the geometric quantities, i.e., radius of Poincare sphere and geometric phase. We find that the mixing process between electron and muon neutrinos can be described by the radius of Poincare sphere that depends on the intrinsic CP-violating angle. Such a radius reveals a dynamic mechanism of CPT-violation, i.e., both spontaneous symmetry breaking and Majorana-Dirac neutrino confusion. We show that the time-dependent geometric phase can be used to find the neutrino nature and observe the CPT-violation because it is strongly enhanced under the neutrino propagation. We further show that the time-dependent geometric phase can be easily detected by simulating the neutrino oscillation based on fluctuating magnetic fields in nuclear magnetic resonance, which makes the experimental observation of CPT-violation possible in the neutrino mixing and oscillation.
Stephen Angus🇰🇷 · Cyril Matti🇬🇧 · Eirik Eik Svanes🇫🇷
We continue the investigation into non-maximally symmetric compactifications of the heterotic string. In particular, we consider compactifications where the internal space is allowed to depend on two or more external directions. For preservation of supersymmetry, this implies that the internal space must in general be that of a manifold, which leads to a -BPS four-dimensional supersymmetric perturbative vacuum breaking all but one supercharge. We find that these solutions allow for internal geometries previously excluded by the domain-wall-type solutions, and hence the resulting four-dimensional superpotential is more generic. In particular, we find an interesting resemblance to the superpotentials that appear in non-geometric flux compactifications of type II string theory. If the vacua are to be used for phenomenological applications, they must be lifted to maximal symmetry by some non-perturbative or higher-order effect.
Gamma-ray bursts (GRBs) were confirmed to be of extragalactic origin due to their isotropic angular distribution, combined with the fact that they exhibited an intensity distribution that deviated strongly from the power law. This finding was later confirmed with the first redshift, equal to at least , measured for GRB970508. Despite this result, the data from /BATSE and /BAT indicate that long GRBs are indeed distributed isotropically, but the distribution of short GRBs is anisotropic. /GBM has detected 1669 GRBs up to date, and their sky distribution is examined in this paper. A number of statistical tests is applied: nearest neighbour analysis, fractal dimension, dipole and quadrupole moments of the distribution function decomposed into spherical harmonics, binomial test, and the two point angular correlation function. Monte Carlo benchmark testing of each test is performed in order to evaluate its reliability. It is found that short GRBs are distributed anisotropically on the sky, and long ones have an isotropic distribution. The probability that these results are not a chance occurence is equal to at least 99.98\% and 30.68\% for short and long GRBs, respectively. The cosmological context of this finding and its relation to large-scale structures is discussed.
Pierre Moreau🇩🇪 · Olena Linnyk🇩🇪 · Wolfgang Cassing🇩🇪 · Elena Bratkovskaya🇩🇪
The Parton-Hadron-String-Dynamics (PHSD) transport model is used to study the impact on the choice of initial degrees of freedom on the final hadronic and electromagnetic observables in Au+Au collisions at = 200 GeV. We find that a non-perturbative system of massive gluons (scenario I) and a system dominated by quarks and antiquarks (scenario II) lead to different hadronic observables when imposing the same initial energy-momentum tensor just after the passage of the impinging nuclei. In case of the gluonic initial condition the formation of pairs in the QGP proceeds rather slow such that the anti-strange quarks and accordingly the mesons do not achieve chemical equilibrium even in central Au+Au collisions at = 200 GeV. Accordingly, the rapidity distribution is suppressed in the gluonic scenario and in conflict with the data from the BRAHMS Collaboration. The proton and antiproton rapidity distributions also disfavor the scenario I. Furthermore, a clear suppression of direct photon and dilepton production is found for the pure gluonic initial conditions which is not so clearly seen in the present photon and dilepton spectra from Au+Au collisions at = 200 GeV due to a large contribution from other channels. It is argued that dilepton spectra in the invariant mass range 1.2 GeV 3 GeV will provide a definitive answer once the background from correlated -meson decays is subtracted experimentally.
Peter Tinyakov🇧🇪 · Igor Tkachev🇷🇺 · Konstantin Zioutas🇬🇷
In some axion dark matter models a dominant fraction of axions resides in dense small-scale substructures, axion miniclusters. A fraction of these substructures is disrupted and forms tidal streams where the axion density may still be an order of magnitude larger than the average. We discuss implications of these streams for the direct axion searches. We estimate the fraction of disrupted miniclusters and the parameters of the resulting streams, and find that stream-crossing events would occur at a rate of about for 2-3 days, during which the signal in axion detectors would be amplified by a factor . These estimates suggest that the effect of the tidal disruption of axion miniclusters may be important for direct axion searches and deserves a more thorough study.
In this paper we study a new class of inflation models which generalize the Dirac-Born-Infeld (DBI) action with the addition of a nonminimal kinetic coupling (NKC) term. We dubbed this model as the {\it new DBI inflation model}. The NKC term does not bring new dynamical degree of freedom, so the equations of motion remain of second order. However, with such a coupling, the action is no longer linear with respect to the Einstein curvature term ( or ), which leads to a correction term of in the perturbations. The new DBI inflation model can be viewed as theories beyond Horndeski. Without violating nearly scale-invariance, such a correction may lead to new effects on the inflationary spectra that could be tested by future observations.
* 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.