Search

We discuss the following proposition: Renormalization Group flow of quantum theory with a biased symmetry exhibits a fixed hypersurface at which the symmetry is exact. Such emergent symmetries may have important phenomenological implications, including supersymmetric models, gauge theories, and massive gravity. Most interesting example is an emergent supersymmetry in non-abelian gauge theories with appropriate field content, in the IR limit i.e. strong coupling regime., Comment: 10 pages, 6 figures

The Standard Model does not constrain the form of the Yukawa matrices and thus the origin of fermion mass hierarchies and mixing pattern remains puzzling. On the other hand, there are intriguing relations between the quark masses and their weak mixing angles, such as the well-known one $\tan \theta_C= \sqrt{m_d/m_s}$ for the Cabibbo angle, which may point towards specific textures of Yukawa matrices hypothesized by Harald Fritzsch at the end of the 70's. Though the original ansatz of Fritzsch is excluded by the experimental data, one can consider its minimal modification which consists in introducing an asymmetry between the 23 and 32 entries in the down-quark Yukawa matrix. We show that this structure is perfectly compatible with the present precision data on quark masses and CKM mixing matrix, and theoretically it can be obtained in the context of $SU(5)$ model with inter-family $SU(3)_H$ symmetry. We also discuss some alternative approaches which could give a natural description of the fermion mass spectrum and weak mixing pattern., Comment: Contribution to the volume in memory of Harald Fritzsch. arXiv admin note: text overlap with arXiv:2305.00069

The Standard Model does not constrain the form of the Yukawa matrices and thus the origin of fermion mass hierarchies and mixing pattern remains puzzling. On the other hand, there are intriguing relations between fermion masses and mixing angles which may point towards specific textures of Yukawa matrices. One of the classic hypothesis is the zero texture proposed by Fritzsch which is, however, excluded by present precision tests since it predicts a too large value of $|V_{cb}|$ as well as a too small value of the ratio $|V_{ub}/V_{cb}|$. In this paper we discuss a minimal modification which still maintains the six zero entries as in the original Fritzsch ansatz. This modification consists in introducing an asymmetry between the 23 and 32 entries in the down-quark Yukawa matrix. We show that this flavour structure can naturally emerge in the context of models with inter-family $SU(3)_H$ symmetry. We present a detailed analysis of this Fritzsch-like texture by testing its predictions and showing that it is perfectly compatible with the present precision data on quark masses and CKM mixing matrix.

The possibility that a neutron can be transformed to a hidden sector particle remains intriguingly open. Proposed theoretical models conjecture that the hidden sector can be represented by a mirror sector, and the neutron n can oscillate into its sterile mirror twin n', exactly or nearly degenerate in mass with n. Oscillations n - n' can take place in vacuum and in the environment of the regular matter and the magnetic field where only neutron will be subject of interaction with the environment. We describe the propagation of the oscillating n - n' system as a particle of the cold neutron beam passing through the dense absorbing materials in connection with the possible regeneration type of experiments where the effect of n -> n' -> n transformation can be observed., Comment: 12 pages, 3 figures, submitted to MDPI "Symmetry" journal

The field of particle physics is at the crossroads. The discovery of a Higgs-like boson completed the Standard Model (SM), but the lacking observation of convincing resonances Beyond the SM (BSM) offers no guidance for the future of particle physics. On the other hand, the motivation for New Physics has not diminished and is, in fact, reinforced by several striking anomalous results in many experiments. Here we summarise the status of the most significant anomalies, including the most recent results for the flavour anomalies, the multi-lepton anomalies at the LHC, the Higgs-like excess at around 96 GeV, and anomalies in neutrino physics, astrophysics, cosmology, and cosmic rays. While the LHC promises up to 4/ab of integrated luminosity and far-reaching physics programmes to unveil BSM physics, we consider the possibility that the latter could be tested with present data, but that systemic shortcomings of the experiments and their search strategies may preclude their discovery for several reasons, including: final states consisting in soft particles only, associated production processes, QCD-like final states, close-by SM resonances, and SUSY scenarios where no missing energy is produced. New search strategies could help to unveil the hidden BSM signatures, devised by making use of the CERN open data as a new testing ground. We discuss the CERN open data with its policies, challenges, and potential usefulness for the community. We showcase the example of the CMS collaboration, which is the only collaboration regularly releasing some of its data. We find it important to stress that individuals using public data for their own research does not imply competition with experimental efforts, but rather provides unique opportunities to give guidance for further BSM searches by the collaborations. Wide access to open data is paramount to fully exploit the LHCs potential., Comment: Whitepaper including input from the workshop "Unveiling Hidden Physics Beyond the Standard Model at the LHC" (1-3 March 2021, online), 70 pages plus references, 17 figures, 7 tables

The oscillation of the neutron $n$ into mirror neutron $n'$, its partner from dark mirror sector, can gradually transform an ordinary neutron star into a mixed star consisting in part of mirror dark matter. The implications of the reverse process taking place in the mirror neutron stars depend on the sign of baryon asymmetry in mirror sector. Namely, if it is negative, as predicted by certain baryogenesis scenarios, then $\bar{n}'-\bar{n}$ transitions create a core of our antimatter gravitationally trapped in the mirror star interior. The annihilation of accreted gas on such antimatter cores could explain the origin $\gamma$-source candidates, with unusual spectrum compatible to baryon-antibaryon annihilation, recently identified in the Fermi LAT catalog, In addition, some part of this antimatter escaping after the mergers of mirror neutron stars can produce the flux of cosmic antihelium and also heavier antinuclei which are hunted in the AMS-02 experiment., Comment: 11 pages

Recent high precision determinations of $V_{us}$ and $V_{ud}$ indicate towards anomalies in the first row of the CKM matrix. Namely, determination of $V_{ud}$ from superallowed beta decays and of $V_{us}$ from kaon decays imply a violation of first row unitarity at about $4\sigma$ level. Moreover, there is tension between determinations of $V_{us}$ obtained from leptonic $K\mu2$ and semileptonic $K\ell3$ kaon decays. These discrepancies can be explained if there exist extra vector-like quarks at the TeV scale, which have large enough mixings with the lighter quarks. In particular, extra vector-like weak singlets quarks can be thought as a solution to the CKM unitarity problem and an extra vector-like weak doublet can in principle resolve all tensions. The implications of this kind of mixings are examined against the flavour changing phenomena and SM precision tests. We consider separately the effects of an extra down-type isosinglet, up-type isosinglet and an isodoublet containing extra quarks of both up and down type, and determine available parameter spaces for each case. We find that the experimental constraints on flavor changing phenomena become more stringent with larger masses, so that the extra species should have masses no more than few TeV. Moreover, only one type of extra multiplet cannot entirely explain all the discrepancies, and some their combination is required. We show that these scenarios are testable with future experiments. Namely, if extra vector-like quarks are responsible for CKM anomalies, then at least one of them should be found at scale of few TeV, and anomalous weak isospin violating $Z$-boson couplings with light quarks should be detected if the experimental precision on $Z$ hadronic decay rate is improved by a factor of $2$ or so., Comment: 92 pages, 24 figures

The oscillation of neutrons $n$ into mirror neutrons $n'$, their mass degenerate partners from dark mirror sector, can have interesting implications for neutron stars: an ordinary neutron star could gradually transform into a mixed star consisting in part of mirror dark matter. Mixed stars can be detectable as twin partners of ordinary neutron stars: namely, there can exist compact stars with the same masses but having different radii. For a given equation of state (identical between the ordinary and mirror components), the mass and radius of a mixed star depend on the proportion between the ordinary and mirror components in its interior which in turn depends on its age. If $50 \% - 50\%$ proportion between two fractions can be reached asymptotically in time, then the maximum mass of such "maximally mixed stars" should be $\sqrt2$ times smaller than that of ordinary neutron star while the stars exceeding a critical mass value $M^{\rm max}_{NS}/\sqrt2$ should collapse in black holes after certain time. We evaluate the evolution time and discuss the implications of $n-n'$ transition for the pulsar observations as well as for the gravitational waves from the neutron star mergers and associated electromagnetic signals., Comment: 18 pages, 6 figures

The origin of the matter-antimatter asymmetry apparently obligates the laws of physics to include some mechanism of baryon number ($\mathcal{B}$) violation. Searches for interactions violating $\mathcal{B}$ and baryon-minus-lepton number $\mathcal{(B-L)}$ represent a rich and underutilized opportunity. These are complementary to the existing, broad program of searches for $\mathcal{L}$-violating modes such as neutrinoless double $\beta$-decay which could provide deeper understandings of the plausibility of leptogenesis, or $\mathcal{B}$-violating, $\mathcal{(B-L)}$-conserving processes such as proton decay. In particular, a low-scale, post-sphaleron violation mechanism of $\mathcal{(B-L)}$ could provide a \textit{testable} form of baryogenesis. Though theoretically compelling, searches for such $\mathcal{(B-L)}$-violating processes like $\Delta\mathcal{B}=2$ dinucleon decay and $n\rightarrow\bar{n}$ remain relatively underexplored experimentally compared to other rare processes. By taking advantage of upcoming facilities such as the Deep Underground Neutrino Experiment and the European Spallation Source, this gap can be addressed with new intranuclear and free searches for neutron transformations with very high sensitivity, perhaps greater than three orders of magnitude higher than previous experimental searches. This proceedings reports on recent theoretical and experimental advances and sensitivities of next-generation searches for neutron transformations were detailed as part of the Amherst Center for Fundamental Interactions Workshop, "Theoretical Innovations for Future Experiments Regarding Baryon Number Violation," directly coordinated with the Rare Processes and Precision Measurements Frontier., Comment: Amherst Center for Fundamental Interactions workshop proceedings with short and long abstracts

Existing bounds on the neutron-antineutron mass mixing, $\epsilon_{n\bar n} < {\rm few} \times 10^{-24}$ eV, impose a severe upper limit on $n - \bar n$ transition probability, $P_{n\bar n}(t) < (t/0.1 ~{\rm s})^2 \times 10^{-18}$ or so, where $t$ is the neutron flight time. Here we propose a new mechanism of $n- \bar n$ transition which is not induced by direct mass mixing $\epsilon_{n\bar n}$ but is mediated instead by the neutron mixings with the hypothetical states of mirror neutron $n'$ and mirror antineutron $\bar{n}'$. The latter can be as large as $\epsilon_{nn'}, \epsilon_{n\bar{n}'} \sim 10^{-15}$ eV or so, without contradicting present experimental limits and nuclear stability bounds. The probabilities of $n-n'$ and $n-\bar{n}'$ transitions, $P_{nn'}$ and $P_{n\bar{n}'}$, depend on environmental conditions in mirror sector, and they can be resonantly amplified by applying the magnetic field of the proper value. This opens up a possibility of $n-\bar n$ transition with the probability $P_{n\bar n} \simeq P_{nn'} P_{n\bar{n}'}$ which can reach the values $\sim 10^{-8} $ or even larger. For finding this effect in real experiments, the magnetic field should not be suppressed but properly varied. These mixings can be induced by new physics at the scale of few TeV which may also originate a new low scale co-baryogenesis mechanism between ordinary and mirror sectors., Comment: 10 pages

After the recent high precision determinations of $V_{us}$ and $V_{ud}$, the first row of the CKM matrix shows more than $4\sigma$ deviation from unitarity. Two possible scenarios beyond the Standard Model can be investigated in order to fill the gap. If a 4th quark $b'$ participates in the mixing, with $\vert V_{ub'} \vert \sim0.04$, then its mass should be no more than 6 TeV or so. A different solution can come from the introduction of the gauge horizontal family symmetry acting between the lepton families and spontaneously broken at the scale of about 6 TeV. Since the gauge bosons of this symmetry contribute to muon decay in positive interference with Standard Model, the Fermi constant is slightly smaller than the muon decay constant so that unitarity is recovered. Also the neutron lifetime problem, that is about $4\sigma$ discrepancy between the neutron lifetimes measured in beam and trap experiments, is discussed in the light of the these determinations of the CKM matrix elements., Comment: 11 pages, 10 figures

The neutron, besides its $\beta$-decay $n\to p e\bar\nu_e$, might have a new decay channel $n\to n' X$ into mirror neutron $n'$, its nearly mass degenerate twin from parallel dark sector, and a massless boson $X$ which can be ordinary and mirror photons or some more exotic particle. Such an invisible decay could alleviate the tension between the neutron lifetimes measured in the beam and trap experiments. I discuss some phenomenological and astrophysical consequences of this scenario, which depends on the mass range of mirror neutron $n'$. Namely, the case $m_{n'} < m_p + m_e$ leads to a striking possibility is that the hydrogen atom $^1$H (protium), constituting 75 per cent of the baryon mass in the Universe, could in fact be unstable: it can decay via the electron capture into $n'$ and $\nu_e$, with relatively short lifetime $\sim 10^{21}$ yr or so. If instead $m_{n'} > m_p + m_e$, then the decay $n'\to pe\bar \nu_e$ is allowed and $n'$ can represent an unstable dark matter component with rather large lifetime exceeding the age of the Universe. Nevertheless, this decay would produce substantial diffuse gamma background. The dark decay explanation of the lifetime puzzle, however, has a tension with the last experimental results measuring $\beta$-asymmetry in the neutron decay., Comment: 11 pages, 4 figures

We discuss the possibility of the transition magnetic moments (TMM) between the neutron n and mirror neutron n', its hypothetical sterile twin from parallel particle "mirror" sector. The neutron can be spontaneously converted into mirror neutron via these TMM's (in addition to the more conventional transition channel due to n-n' mass mixing) interacting with the magnetic field B as well as with mirror magnetic field B'. We derive analytic formula for the average probability of n-n' oscillation and consider possible manifestations of the neutron TMM effects. In particular, we discuss potential role of these effects in the neutron lifetime measurement experiments leading us to new, testable predictions., Comment: 24 pages, 2 figures

Spontaneous breaking of inter-family (horizontal) gauge symmetries can be at the origin of the mass hierarchy between the fermion families. The corresponding gauge bosons have flavor-nondiagonal couplings which generically induce the flavour changing phenomena, and this puts strong lower limits on the flavor symmetry breaking scales. However, in the special choices of chiral horizontal symmetries the flavor changing effects can be naturally suppressed. For the sake of demonstration, we consider the case of leptonic gauge symmetry $SU(3)_e$ acting between right-handed leptons and show that the respective gauge bosons can have mass in the TeV range, without contradicting the existing experimental limits., Comment: 9 pages, 2 figures

We analyze status of ${\bf C}$, ${\bf P}$ and ${\bf T}$ discrete symmetries in application to neutron-antineutron transitions breaking conservation of baryon charge ${\cal B}$ by two units. At the level of free particles all these symmetries are preserved. This includes ${\bf P}$ reflection in spite of the opposite internal parities usually ascribed to neutron and antineutron. Explanation, which goes back to the 1937 papers by E. Majorana and by G. Racah, is based on a definition of parity satisfying ${\bf P}^{2}=-1$, instead of ${\bf P}^{2}=1$, and ascribing $ {\bf P}=i$ to both, neutron and antineutron. We apply this to ${\bf C}$, ${\bf P}$ and ${\bf T}$ classification of six-quark operators with $|\Delta {\cal B} |=2$. It allows to specify operators contributing to neutron-antineutron oscillations. Remaining operators contribute to other $|\Delta {\cal B} |=2$ processes and, in particular, to nuclei instability. We also show that presence of external magnetic field does not induce any new operator mixing the neutron and antineutron provided that rotational invariance is not broken., Comment: 8 pages, 2 figures. arXiv admin note: text overlap with arXiv:1506.05096

The discrepancy between the neutron lifetimes measured in the beam and trap experiments can be explained via the neutron $n$ conversion into mirror neutron $n'$, its dark partner from parallel mirror sector, provided that $n$ and $n'$ have a tiny mass splitting order $10^{-7}$ eV. In large magnetic fields used in beam experiments $n-n'$ transition is resonantly enhanced and can transform of about a per cent fraction of neutrons into mirror neutrons which decay in invisible mode. Thus less protons will be produced and the measured value $\tau_{\rm beam}$ appears larger than $\beta$-decay time $\tau_{\beta} = \tau_{\rm trap}$. Some phenomenological and astrophysical consequences of this scenario are also briefly discussed., Comment: 6 pages, 2 figures

The purpose of this paper is to demonstrate that if the transformation of a neutron to a mirror neutron exists with an oscillation time of the order of ten seconds, it can be detected in a rather simple disappearance and/or regeneration type experiment with an intense beam of cold neutrons. In the presence of a conjectural mirror magnetic field of unknown magnitude and direction, the resonance transformation conditions can be found by scanning the magnitude of the ordinary magnetic field in the range e.g. $\pm 100 \mu$T. Magnetic field is assumed to be uniform along the path of neutron beam. If the transformation effect exists within this range, the direction and possible time variation of the mirror magnetic field can be determined with additional dedicated measurements., Comment: 19 pages, 4 figures, Revised paper

Transformation of neutron to antineutron is a small effect that has not yet been experimentally observed. %\cite{Phillips:2014fgb}. In principle, it can occur with free neutrons in the vacuum or with bound neutrons inside the nuclear environment different for neutrons and antineutrons and for that reason in the latter case it is heavily suppressed. Free neutron transformation also can be suppressed if environmental vector field exists destinguishing neutron from antineutron. We consider here the case of a vector field coupled to $B-L$ charge of the particles ($B-L$ photons) and study a possibility of this to lead to the observable suppression of neutron to antineutron transformation. The suppression effect however can be removed by applying external magnetic field. If the neutron--antineutron oscillation will be discovered in free neutron oscillation experiments, this will imply limits on $B-L$ photon coupling constant and interaction radius few order of magnitudes stronger than present limits form the tests of the equivalence principle. If $n-\bar n$ oscillation will be discovered via nuclear instability, but not in free neutron oscillations in corresponding level, this would indicate to the presence of fifth-forces mediated by such baryophotons., Comment: 13 pages, 4 figures

B and L violating interactions of ordinary particles with their twin particles from hypothetical mirror world can co-generate baryon asymmetries in both worlds in comparable amounts, $\Omega'_B/\Omega_B \sim 5$ or so. On the other hand, the same interactions induce the oscillation phenomena between the neutral particles of two sectors which convert e.g. mirror neutrons into our antineutrons. These oscillations are environment dependent and can have fascinating physical consequences., Comment: 4 pages, no figures

We discuss a possibility that baryon number $B$ is spontaneously broken at low scales, of the order of MeV or even smaller, so that the neutron-antineutron oscillation can be induced at the experimentally accessible level. An associated Goldstone particle, baryonic majoron, can have observable effects in neutron to antineutron transitions in nuclei or dense nuclear matter. By extending baryon number to $B-L$ symmetry, baryo-majoron can be identified with the ordinary majoron associated with the spontaneous breaking of lepton number, with interesting implications for neutrinoless $2\beta$ becay with the majoron emission, etc. We also discuss a hypothesis suggesting that baryon number maybe spontaneously broken by the QCD itself via the six-quark condensates., Comment: 8 pages, 5 figures

The excess of high energy neutrinos observed by the IceCube collaboration might originate from baryon number violating decays of heavy shadow baryons from dark mirror sector which produce shadow neutrinos. These sterile neutrino species then oscillate into ordinary neutrinos transferring to them specific features of their spectrum. In particular, this scenario can explain the end of the spectrum above 2 PeV and the presence of the energy gap between 400 TeV and 1 PeV., Comment: 4 pages, 3 figures, talk given at Int. Workshop NOW 2014, 7-14 Sept. 2014, Conca Specchiula, Italy

Assuming the Lorentz and CPT invariances we show that neutron-antineutron oscillation implies breaking of CP along with baryon number violation -- i.e. two of Sakharov conditions for baryogenesis. The oscillation is produced by the unique operator in the effective Hamiltonian. This operator mixing neutron and antineutron preserves charge conjugation C and breaks P and T. External magnetic field always leads to suppression of oscillations. Its presence does not lead to any new operator mixing neutron and antineutron., Comment: 6 pages, 2 figures. More detailed argumentation is presented

The magic couple of SUSY and GUT still appears the most elegant and predictive physics concept beyond the Standard Model. Since up to now LHC found no evidence for supersymmetric particles it becomes of particular relevance to determine an upper bound of the energy scale they have to show up. In particular, we have analyzed a generic SUSY-GUT model assuming one step unification like in SU(5), and adopting naturalness principles, we have obtained general bounds on the mass spectrum of SUSY particles. We claim that if a SUSY gauge coupling unification takes place, the lightest gluino or Higgsino cannot have a mass larger than about 20 TeV. Such a limit is of interest for planning new accelerator machines., Comment: 23 pages, 5 figures. Version published in JHEP, minor corrections added and images improved

A new scenario for creation of galactic magnetic fields is proposed which is operative at the cosmological epoch of the galaxy formation, and which relies on unconventional properties of dark matter. Namely, it requires existence of feeble but long range interaction between the dark matter particles and electrons. In particular, millicharged dark matter particles or mirror particles with the photon kinetic mixing to the usual photon can be considered. We show that in rotating protogalaxies circular electric currents can be generated by the interactions of free electrons with dark matter particles in the halo, while the impact of such interactions on galactic protons is considerably weaker. The induced currents may be strong enough to create the observed magnetic fields on the galaxy scales with the help of moderate dynamo amplification. In addition, the angular momentum transfer from the rotating gas to dark matter component could change the dark matter profile and formation of cusps at galactic centers would be inhibited. The global motion of the ionized gas could produce sufficiently large magnetic fields also in filaments and galaxy clusters., Comment: 8 pages, refined version published in Eur. Phys. J. C73, 2620 (2013)

Part 2 of "Project X: Accelerator Reference Design, Physics Opportunities, Broader Impacts". In this Part, we outline the particle-physics program that can be achieved with Project X, a staged superconducting linac for intensity-frontier particle physics. Topics include neutrino physics, kaon physics, muon physics, electric dipole moments, neutron-antineutron oscillations, new light particles, hadron structure, hadron spectroscopy, and lattice-QCD calculations. Part 1 is available as arXiv:1306.5022 [physics.acc-ph] and Part 3 is available as arXiv:1306.5024 [physics.acc-ph]., Comment: 209 pp. with many figures; prepared in part for the DPF Community Summer Study; v2 corrects typos (including one author surname), adds an author, and conforms with the version being printed; v3 includes two more chapter authors in full list at the top

Effects of light millicharged dark matter particles on primordial nucleosynthesis are considered. It is shown that if the mass of such particles is much smaller than the electron mass, they lead to strong overproduction of Helium-4. An agreement with observations can be achieved by non-vanishing lepton asymmetry. Baryon-to-photon ratio at BBN and neutrino- to-photon ratio both at BBN and at recombination are noticeably different as compared to the standard cosmological model. The latter ratio and possible lepton asymmetry could be checked by Planck. For higher mass of new particles the effect is much less pronounced and may even have opposite sign., Comment: Replaced with the version accepted for publication in JCAP

Present experimental data do not exclude fast oscillation of the neutron $n$ to its degenerate twin from a hypothetical parallel sector, the so called mirror neutron $n'$. We show that this effect brings to a remarkable modifications of the ultrahigh-energy cosmic ray spectrum testable by the present Pierre Auger Observatory (PAO) and Telescope Array (TA) detector, and the future JEM-EUSO experiment. In particular, the baryon non-conservation during UHECR propagation at large cosmological distances shifts the beginning of the GZK cutoff to lower energies, while in presence of mirror sources it may enhance the spectrum at $E \gtrsim 100$ EeV. As a consequence, a significant reduction of the expected diffuse cosmogenic neutrino flux is predicted., Comment: 7 pages, 3 figures. Final version published in Eur. Phys. J. C

We discuss astrophysical implications of the modified gravity model in which the two matter components, ordinary and dark, couple to separate gravitational fields that mix to each other through small mass terms. There are two spin-2 eigenstates: the massless graviton that induces universal Newtonian attraction, and the massive one that gives rise to the Yukawa-like potential which is repulsive between the ordinary and dark bodies. As a result the distances much smaller than the Yukawa radius $r_m$ the gravitation strength between the two types of matter becomes vanishing. If $r_m \sim 10$ kpc, a typical size of a galaxy, there are interesting implications for the nature of dark matter. In particular, one can avoid the problem of the cusp that is typical for the cold dark matter halos. Interestingly, the flat shape of the rotational curves can be explained even in the case of the collisional and dissipative dark matter (as e.g. mirror matter) that cannot give the extended halos but instead must form galactic discs similarly to the visible matter. The observed rotational curves for the large, medium-size and dwarf galaxies can be nicely reproduced. We also briefly discuss possible implications for the direct search of dark matter., Comment: 11 pages, 12 figures

The nature of the gravitational interaction between ordinary and dark matter is still open. Any deviation from universality or the Newtonian law also modifies the standard assumption of collisionless dark matter. On the other hand, obtaining a Yukawa-like large-distance modification of the gravitational potential is a nontrivial problem, that has so far eluded a consistent realization even at linearized level. We propose here a theory providing a Yukawa-like potential, by coupling non-derivatively the two metric fields related respectively to the visible and dark matter sectors, in the context of massive gravity theories where the local Lorentz invariance is broken by the different coexisting backgrounds. This gives rise to the appropriate mass pattern in the gravitational sector, producing a healthy theory with the Yukawa potential. Our results are of a special relevance in the scenario of dark matter originated from the mirror world, an exact duplicate of the ordinary particle sector., Comment: 19 pages

Mirror world, a parallel hidden sector with microphysics identical to ordinary particle physics, can have several interesting phenomenological and astrophysical implications and mirror matter can be a natural candidate for dark matter in the universe. If the ordinary and the mirror photons have a kinetic mixing due to the Lagrangian term $(\epsilon/2) F_{\mu\nu} F'^{\mu\nu}$, then mirror particles effectively acquire the electric charges $\sim \epsilon$ with respect to the ordinary photon, so that they become a sort of particles historically coined as "millicharged" though nowadays they must be called more appropriately as "nanocharged". In this paper we revise the cosmological bounds on the kinetic mixing parameter and in the case of exact mirror parity set an upper limit $\epsilon < 3 \times 10^{-10}$. Much weaker limit can be obtained in the case of asymmetric mirror sector, with an electroweak symmetry breaking scale larger than the ordinary electroweak scale., Comment: 12 pages, 1 figure, corrected typos, changed figure, some references added or removed, some explanations added according to the referee's suggestions

It was pointed out recently that oscillation of the neutron $n$ into mirror neutron $n'$, a sterile twin of the neutron with exactly the same mass, could be a very fast process with the the baryon number violation, even faster than the neutron decay itself. This process is sensitive to the magnetic fields and it could be observed by comparing the neutron lose rates in the UCN storage chambers for different magnetic backgrounds. We calculate the probability of $n-n'$ oscillation in the case when a mirror magnetic field $\vec{B}'$ is non-zero and show that in this case it can be suppressed or resonantly enhanced by applying the ordinary magnetic field $\vec{B}$, depending on its strength and on its orientation with respect to $\vec{B}'$. The recent experimental data, under this hypothesis, still allow the $n-n'$ oscillation time order 1 s or even smaller. Moreover, they indicate that the neutron losses are sensitive to the orientation of the magnetic field. %at about $3\sigma$ level. If these hints will be confirmed in the future experiments, this would point to the presence of the mirror magnetic field on the Earth of the order of 0.1 G, or some equivalent spin-dependent force of the other origin that makes a difference between the neutron and mirror neutron states., Comment: 10 pages

The baryonic and dark matter fractions in the universe can be both generated by the same baryogenesis mechanism, simultaneously and with comparable amounts, if dark matter is constituted by the baryons of the mirror world, a parallel hidden sector with the same (or similar) microphysics as that of the observable world., Comment: 8 pages, invited talk at the "Dark Side of the Universe" DSU 2006, Madrid, 19-24 June 2006

We show that in supersymmetric grand unified theories new effective D=4 and D=5 operators for proton decay are induced by soft SUSY-breaking terms, when heavy GUT gauge bosons are integrated out, in addition to the standard D=6 ones. As a result, the proton lifetime in gauge mediated channels can be enhanced or even suppressed depending on the size of the heavy Higgses soft terms., Comment: 16 pages, 2 figures, LaTeX, JHEP3 class, axodraw

If there exists the mirror world, a parallel hidden sector of particles with exactly the same microphysics as that of the observable particles, then the primordial nucleosynthesis constraints require that the temperature of the cosmic background of mirror relic photons should be smaller than that of the ordinary relic photons, T'/T < 0.5 or so. On the other hand, the present experimental and astrophysical limits allow a rather fast neutron - mirror neutron oscillation in vacuum, with an oscillation time $\tau \sim 1$ s, much smaller than the neutron lifetime. We show that this could provide a very efficient mechanism for transporting ultra high energy protons at large cosmological distances. The mechanism operates as follows: a super-GZK energy proton scatters a relic photon producing a neutron that oscillates into a mirror neutron which then decays into a mirror proton. The latter undergoes a symmetric process, scattering a mirror relic photon and producing back an ordinary nucleon, but only after traveling a distance $(T/T')^{3}$ times larger than ordinary protons. This may relax or completely remove the GZK-cutoff in the cosmic ray spectrum and also explain the correlation between the observed ultra high energy protons and far distant sources as are the BL Lacs., Comment: 14 pages; to appear in PLB (submitted 28 November 2005)

This paper has been withdrawn by the authors to avoid redundancy with e-print hep-ph0507031., Comment: withdrawn to avoid redundancy with e-print hep-ph0507031

A mechanism of double protection of the Higgs potential, by supersymmetry and by a global symmetry, is investigated in a class of supersymmetric models with the SU(3)xSU(3)xU(1) gauge symmetry. In such models the electroweak symmetry can be broken with no fine-tuning at all., Comment: 10 pages, 2 figures, latex; v2: typos corrected, references added, new paragraph on decoupling D-terms

We briefly review the concept of a parallel `mirror' world which has the same particle physics as the observable world and couples to the latter by gravity and perhaps other very weak forces. The nucleosynthesis bounds demand that the mirror world should have a smaller temperature than the ordinary one. By this reason its evolution should substantially deviate from the standard cosmology as far as the crucial epochs like baryogenesis, nucleosynthesis etc. are concerned. In particular, we show that in the context of certain baryogenesis scenarios, the baryon asymmetry in the mirror world should be larger than in the observable one. Moreover, we show that mirror baryons could naturally constitute the dominant dark matter component of the Universe, and discuss its cosmological implications., Comment: Published in Ian Kogan Memorial Collection "From Fields to Strings: Circumnavigating Theoretical Physics", Eds. M. Shifman et al., World Scientific, Singapore, vol. 3, pp. 2147-2195. 49pp., 8 Figures

There can exist a hidden sector of the Universe in the form of parallel ''mirror'' world which has the same particle physics as the observable world and interacts with the latter only gravitationally. Big Bang Nucleosynthesis bounds demand that the mirror sector should have a smaller temperature than the ordinary one. This implies that the mirror matter could play a role of dark matter, and in addition its chemical content should be dominated by helium. Here we study the evolutionary and structural properties of the mirror stars which essentially are similar to that of the ordinary stars but with higher helium contents. Being invisible in terms of photons, they could be observed only as MACHOs in the microlensing experiments. Using a numerical code, we compute evolution of stars with large helium abundances (Y = 0.30-0.80) and a wide range of masses, from 0.5 to 10 solar masses. We found that helium dominated mirror star should have much faster evolutionary time (up to a factor 30) than the ordinary star with the same mass. In addition, we show the diagrams of luminosities, effective temperatures, central temperatures and densities, and compute the masses of the He core at ignition and the minimum mass for carbon ignition, for different chemical compositions. The general conclusion is that mirror stars evolve faster as compared to ordinary ones, and explode earlier as type II supernovae, thus enriching the galactic halo of processed mirror gas with higher metallicity, with implications for MACHO observations and galaxy evolution., Comment: 24 pages, 10 figures; minor changes

In the mirror world hypothesis the mirror baryonic component emerges as a possible dark matter candidate. An immediate question arises: how the mirror baryons behave and what are the differences from the more familiar dark matter candidates as e.g. cold dark matter? In this paper we answer quantitatively to this question. First we discuss the dependence of the relevant scales for the structure formation (Jeans and Silk scales) on the two macroscopic parameters necessary to define the model: the temperature of the mirror plasma (limited by the Big Bang Nucleosynthesis) and the amount of mirror baryonic matter. Then we perform a complete quantitative calculation of the implications of mirror dark matter on the cosmic microwave background and large scale structure power spectrum. Finally, confronting with the present observational data, we obtain some bounds on the mirror parameter space., Comment: 11 pages, 6 figures; minor corrections, references added; accepted for publication in IJMPD

We briefly review the concept of a parallel `mirror' world which has the same particle physics as the observable world and couples to the latter by gravity and perhaps other very weak forces. The nucleosynthesis bounds demand that the mirror world should have a smaller temperature than the ordinary one. By this reason its evolution should substantially deviate from the standard cosmology as far as the crucial epochs like baryogenesis, nucleosynthesis etc. are concerned. In particular, we show that in the context of certain baryogenesis scenarios, the baryon asymmetry in the mirror world should be larger than in the observable one. Moreover, we show that mirror baryons could naturally constitute the dominant dark matter component of the Universe, and discuss its cosmological implications.

The present experimental status does not exclude weak-strength non-standard interactions of neutrinos with electrons. These interactions can be revealed in solar neutrino experiments. Our discussion covers several aspects related to this issue. First, we perform an analysis of the Super Kamiokande and SNO data to investigate their sensitivity to such interactions. In particular, we show that the \nu_e oscillation into sterile neutrinos can be still allowed if \nu_e has extra interactions of the proper strength. Second, we suggest that the Borexino detector can provide good signatures for these non-standard interactions. Indeed, in Borexino the shape of the recoil electron spectrum from the \nu e \to \nu e scattering essentially does not depend on the solar neutrino conversion details, since most of the signal comes from the mono-energetic ^7Be neutrinos. Hence, the partial conversion of solar \nu_e into a a nearly equal mixture of \nu_\mu and \nu_\tau, as is indicated by the atmospheric neutrino data, offers the chance to test extra interactions of \nu_\tau, or of \nu_e itself., Comment: 17 LaTeX pages, 15 postscript figures, uses epsfig.sty. More extended discussion about the spectral deformation for both Super-Kamiokande and Borexino; new figures are added

We provide an effective Lagrangian analysis of contact non-standard interactions of neutrinos with electrons, which can be effectively mediated by extra particles, and examine the associated experimental limits. At present, such interactions are strongly constrained only for $\nu_\mu$: the bounds are loose for $\nu_e$ and absent for $\nu_\tau$. We emphasize the unique role played by the reaction $e^+e^-\to \nu \bar{\nu}\gamma$ in providing direct constraints on such non-standard interactions., Comment: 15 LaTeX pages, 6 postscript figures, uses epsfig. New discussion on bounds from reactor anti-neutrino scattering off electrons; minor changes. To appear on Phys. Lett. B

We propose a baryo- and leptogenesis mechanism in which the B-L asymmetry is produced in the conversion of ordinary leptons into particles of some depleted hidden sector. In particular, we consider the lepton number violating reactions, l Higgs -> l' Higgs', \bar{l'} \bar{Higgs'}, mediated by the heavy Majorana neutrinos N of the seesaw mechanism, where l and Higgs are ordinary lepton and Higgs doublets and l', Higgs' the ``sterile'' leptons and Higgs. This mechanism can operate even if the reheat temperature is smaller than the N Majorana masses, in which case the usual leptogenesis mechanism through N decays is ineffective. In particular, the reheat tempearture can be as low as 10^9 GeV or less., Comment: 11 pages, 2 figures; Talk given (LB) at the XI International School: Particles and Cosmology, Baksan Valley, Kabardino-Balkaria, Russia, 18-24 April, 2001

We propose a new mechanism to block the active-sterile neutrino oscillations in the Early Universe. We show that a typical consequence of theories where the lepton number is spontaneously broken is the existence of a coherent cosmological Majoron field with a strength proportional to the lepton and baryon numbers of the Universe. This field interacts with leptons and changes the potentials relevant for neutrino oscillations. If the scale of lepton number symmetry breaking is of the order of 1 GeV then a Majoron field and lepton number asymmetry of the order of the baryon asymmetry are strong enough to block the active-sterile neutrino oscillations with the atmospheric neutrino mass gap which otherwise would bring the sterile neutrino into equilibrium at the big bang nucleosynthesis epoch., Comment: 15 pages, revtex; v3 to match PRD paper

We propose a lepto-baryogenesis mechanism in which the non-zero B-L of the universe is produced in out-of-equilibrium, lepton number and CP violating scattering processes that convert ordinary particles into particles of some hidden sector. In particular, we consider the processes $l \phi > l' \phi', \bar l' \bar phi'$ mediated by the heavy Majorana neutrinos $N$ of the seesaw mechanism, where $l$ and $\phi$ are ordinary lepton and Higgs doublets and $l'$, $\phi'$ their hidden counterparts. Such a leptogenesis mechanism is effective even if the reheating temperature is much smaller than the heavy neutrino masses. In particular, it can be as low as $10^{9}$ GeV., Comment: 4 pages, revtex, 2 figures; as to appear in PRL, supplemented with an additional remark

The onset of inflation in hybrid models require fine tuning in the initial conditions. The inflaton field should have an initial value close to the Planck scale $M_{P}$, whereas the auxiliary "orthogonal" field must be close to zero with an extreme accuracy. This problem can be alleviated if the orthogonal field fastly decays into some states not coupled to the inflaton. Natural candidates for such states can be the right-handed neutrinos. We show that a non-trivial evolution of the classic sneutrino fields after inflation offers an interesting mechanism for generating a correct amount of lepton asymmetry, which being reprocessed by sphalerons can explain the observed baryon asymmetry of the Universe. Our scenario implies interesting bounds for the neutrino masses in the context of seesaw mechanism., Comment: 9 pages, no figures

We discuss the role played by the horizontal flavour symmetry in supersymmetric theories. In particular, we consider the horizontal symmetry $SU(3)_H$ between the three fermion families and show how this concept can help in explaining the fermion mass spectrum and mixing pattern in the context of SUSY GUTs., Comment: 12 LaTeX pages. Talk presented at the Int. Workshop `30 Years of Supersymmetry', Minneapolis, USA, 13-27 Oct. 2000. To appear in Nucl. Phys. Proc. Suppl